Complicated thinking: Why match cylinder porting and barrel length?
 

I got a PM with a pretty good question that I've pondered for some time and come to some explaination for myself, but never shared. I may be right, I may be wrong. I don't have enough emperical observation to back me up, but what the heck. I did a lot of writing to answer his question thoroughly to the best of my understanding so I might as well share here and generate some interesting technical neuron work.

Simplified Questions: Why does TM use ported cylinders apparently matched to barrel lenght? If "barrel suck" is an issue, why not always use unported cylinders? Why do most stock AEGs perform similarly (FPS) even though their barrels are different length?

Setup:
When a mechbox cycles, the motor does the same amount of mechanical work irregardless of the presence of a bb or the cylinder arrangement used assuming that the mainspring force profile remains constant i.e. a full compression cycle of the spring always contains the same amount of potential energy when it's fully compressed.

However, the amount of energy transferred to the bb can be significantly affected by numerous factors. I surmise the following:

A cylinder matched to the barrel:

The piston travels forward pushing air ahead of it. If the piston head is behind the window cut into the cylinder, no air compression is acheived and the air blows out. Since no compression is acheived and the hole is faily large, little work is done in this first phase since the air blows out with little resistance.

Because no significant work is done pushing vented air, most of the potential energy in the spring must be converted to kinetic energy in moving parts up to that point. This means that the piston must be accellerating rapidly and front of the mainspring must be similarly accelerating. Since these two parts are the only two moving parts at this point, their kinetic energy should account for most of the change in potential energy change in the mainspring (conservation of energy).

When the window is finally passed by the piston head, air is trapped and compression begins. Because the piston and spring have absorbed nearly all of the potential energy change in the spring up to this point(actually the centre of gravity of the spring is probably moving about 1/2 the speed of the piston at all times), they're moving pretty quick which means that cylinder pressure should be rising pretty fast. With increased cylinder pressure, an increased backpressure force slows down the piston and spring i.e. kinetic energy is transferring from the piston/spring to compressing air and accelerating the bb (a further fraction transferred to the pellet).

A measured quantity of air is compressed rapidly and accelerates the bb down the barrel.

Unported cylinder and a short barrel:

As soon as the piston begins to move forward, air pressure starts to rise and starts the bb on it's trip down the barrel. Because the cross sectional area of the cylinder is so much larger than the barrel ID, the piston would be moving significantly slower than the bb. As the piston moves forward, air blows the bb down the barrel.

At some point, the bb leaves the barrel and there is no restriction slowing the piston. If the barrel is very short, the piston is still a fair ways from the cylinder so the remaining spring potential energy is converted to kinetic energy in accellerating the piston and front of the spring.

There is no bb present so the remaining potential energy is spent further accelerating the piston/spring which is eventually dissapated in the mechbox when the high energy piston/spring slams into the mechbox.

Conclusimifications:

I am guessing that a matched cylinder/barrel is more efficient than an over long cylinder (or short barrel) because the bb is given the opportunity to absorb kinetic energy from the ENTIRE piston travel. In the case of a matched cylinder, the energy from the initial quick acceleration (window blowby) of the piston is recovered when it rapidly compresses the air in front of the window and socks out the bb.

This energy recovery could be a good explaination why all stock TM AEGs seem to perform the same despite their significant barrel length differences. Notionally a longer barrel should give more time for acceleration. However a ported cylinder means that a shorter cylindered AEG would have a faster initial acceleration so it may perform similarly to a long barreled AEG.

Instead of: long barrel, more fps because of longer acceleration time. The actual situation may be: matched cylinder gives rise to: same stock spring = same energy despite different barrel diameter because of higher or lower acceleration magnitude.


I hope this at least muddies up the waters in an entertaining way.


--Carl

Thanks a lot for the explanation Carl. It does make perfect sense when you think of it.

So there could be significant damage to the mechbox with a unported cylinder and a short barrel? Would there also be a loss of FPS (shorter barrel not allowing the BB time to reach full exit velocity)? Does this mean carbine kits (with shorter inner barrels) for armalites could be potentially damaging mechboxes unless the cylinder is changed?

Thanks,
-Daes-

That could be one problem with M16 cylinders pushing M4 barrels. I can't say without making measurements somehow. As it happens I'm working on a piston head of my own design. A prospective new product for AI. I'm slogging through impact measurement trials at the moment. One day when the damn thing is finished and proven, I could use the impact test apparatus to see if cylinder matching greatly affects mechbox impact.

In the meantime, do not dryfire your mechbox. I can show that dryfire imposes a peak impact force about 60% higher than when firing a 0.2g bb. The situation is even worse when you dryfire test your mechbox without a barrel. Even the barrel can produce a measureable reduction in piston impact.

You know, from what you are saying, if you want to make a quick project, create a barrel plug that will allow dry firing. Alot of people dry fire to see if a battery is working, if you have your plug in, like you should when you store or transport, a plug with an inner resistance tube could be cheap to make, and with the data presented, save the wear and tear on your gun...

Oh yeah, another test that I would like to see, related to this, is the impact difference of having an one-piece and a TM three-piece hopup. Does the quick takedown (armalite) TM hopup leak enough that it is causing more impact when shooting, and especially when dry firing...

=Daes=

TM barrel plugs are already designed to allow for dry firing. That's why they have small holes in them. They create enough pressure to simulate a bb in the barrel, but still allow air to escape so the pressure doesn't build up too high.

I'm not sure how effective the TM barrel plugs are effective in reducing mechbox impact. There isn't much of a good seal between the inner and outer barrel so there might not be much of a cushioning if the air can just rush between inner and outer barrels.

I have actually worked out a bit which can be pressed onto a mechbox nozzle so I can simulate a shot bb when testing a mechbox outside of an AEG (worst case mechbox impact). I also considered a barrel plug for field testing assembled AEGs.

Both items are deferred projects until the piston head testing is completed. I'm timesharing between this airsoft project and a hunk of lab equipment I'm working on so I can't really start any more design projects before none of them get anywhere.

If I didn't need to eat or pay rent, I'd stop retailling airsoft or adaptors so I could put nearly all of my time to getting my design projects done. Unfortunately it kind of defeats the purpose of inventing new stuff if you never take it to market.

the description makes perfect sense in the way i thought of it as well. It's like turbocharged cars and their volumetric effeciency calculations to create high power with properly matched turbo's. After all 10PSI in and almost 10PSI out is more efficient and less power is lost due to excess exhaust heat in the chamber that reduces combustion temps.

Let's get you thinking a little more Carl :) With all that said what do you suspect happens (or not) when you upgrade the bits in the mechbox (stronger spring, spring guide, etc). Will these affect/distort the ratio of the cylinder port/barrel lenght?

What I'm getting at is if I upgrade basically everything in the mechbox should I be looking at a cylinder with different porting or is this not affected at all?

Great stuff Carl, clears the air a bit (once you get by all the conplicated explanationisms.)

Here's a bit of my experience which proves Carl's theory: I have a TM MP5A5/SD "Frankengun" (Primus knows what it looks like....... M4 slither stock and SD front end) that has the basic upgrade of PDI 150% spring and metal bushings. Also have the Hurricane reinforced mechbox (but isn't a performance part, just figured I'd mention). It would shoot pretty damn consistantly (within +/- 2fps for test shots) at 352fps using .2g BBs without hop up. When I was about to install a bearing spring guide, I had Apoc's M733 sitting open on my workbench, and it had a full cylinder in it, compared to my ported MP5 cylinder. I swapped it over to see what would happen. Since my gun was shooting about 350fps, I figured the bearing spring guide should give me around 15fps higher. Once I had the gun back together, I tested it. All shots were sitting around 330fps!?!?

So a 229mm barrel with 150% spring and ported cylinder shot 350fps, but a 229mm barrel with 150% spring, full cylinder and new bearing spring guide shot 330fps. I put the ported cylinder back in, chronied my MP5 again and was shooting about 368fps, and with a bit of hop up, 364fps. So I was right about the spring guide adding 15fps, and was neat to see what the full cylinder did in my gun. Now that I've read Carl's awesome explanation, I can fully see why.

What about a long barrel on a short barrel cylinder?

I ran it to the question in the process of upgrading from my TM G36C to the G36K (see sig). Here is I what I came up with after a lot of thinking and visualizing. (Unfortunately I didn't have any chrony tests.):

Since the compression cycle is starting later because of the port, the bb won't be receiving the proper volume of air compared to the barrel perhaps a slight drop in FPS. Also the piston will start moving back before the bb has left the barrel, so you will get some suck back on it.

I may be completely off. What do you guys think?

I been using a m4 cylinder with my .50 which has a psg-1 tightbore length barrel. Seems to work alright. Chronos about 415-420.

At first I put tape and stuff over the ports but the last time I had it apart I didn't bother.

Anyhow I have a full cylinder I plan on putting in it sometime I take the gearbox apart for maintenence but I not going to do it till then.

anyhow maybe I am getting the dreaded suckback but if I am I certainly don't see it. Don't want the gun shooting much hotter anyhow. hehe

I would guess that a stiffer spring would change ideal matched cylinder.

My reasoning is that an upgrade which results in a higer final bb velocity with the same length barrel would have to apply a higher acceleration rate to the bb. This would require a higher pressure. Actually more like a pressure profile as the pressure probably varies throughout the bb travel.

A higher pressure profile would mean that they cylinder air would compress to a smaller volume and you'd have a higher leak rate around the pellet, nozzle, and nozzle-hop up junction. So if you previously had a perfectly matched cylinder and then you upgraded the spring, you'd have a short cylinder.

However, it's hard to say if you'd actually get barrel suck. Barrel suck is a pretty simple phenomenon if you think of it.

If the:

(cylinder volume - leakage losses) < barrel length

then you don't push enough air to get the bb out the barrel and the bb at some point starts to decellerate in the barrel as it pulls the air below 1atm.

However if the cyl' volume is significantly higher than the barrel volume and the piston head hits the cylinder before the bb leaves it doesn't necessarily mean you get barrel suck. The air pressure behind the bb is still higher than 1atm until the pellet runs down the barrel for awhile. If the pellet leaves just as the volume behind the pellet matches the cylinder volume (plus leakages) then you actually have ideal efficiency.

The actual piston and bb trip times are probably so fast that the idea that the piston would be pulled back by the mechbox before the pellet leaves probably doesn't happen.

Consider an AEG ROF of 900spm ~15shots per sec (0.067sec/shot)

If said AEG shoots at 330fps with a 340mm barrel (1.13')

assume average speed of 165fps (0 at beginning, 330 at end). This implies constant acceleration which is probably not the case, but probably not a bad approximation.

barrel trip time: 1.13ft/165ft/s = 0.00685sec

0.00685sec <<< 0.067/2 (0.0335sec)

I divide the piston cycle time in half because by the time the piston hits the cyl, half the motion cycle has passed. In one more half cycle, they piston will be withdrawn. However this is generous as the piston moves forwards a lot faster than it moves back which means I should allow more time for the sector to come around.

easiest way to measure "barrel suck" would be to measure velocity on single shot and full auto. there would be zero barrel suck on semi as the piston will stop at the end of it's compression stroke and the velocity difference between semi and full would have to be due to barrel suck, all other things being equal. you also brought up an interesting notion on dry firing. so what happens to guns where guys use low-caps and there is always dry firing at the end of each mag (10-15% depending on mag capacity). do these guys put undue stress on their guns when you couple this with the dy firing that occures during testing and weapons clearing. i seriously doubt it. and does the presence of the bb in the chamber, considering losses around the nozzle/cylinder head junction, nozzle/bb junction. bb/barrel gap and around the hop bucking and chamber apply any measurable resistance to the piston in it's stroke? the mass and velocity difference between the piston in motion vs. a bb at rest are so phenominally different not to mention the discharging air at higher pressure in the barrel "feeding back" energy to a larger, lower pressure area like the cylinder, the laws of physics just don't allow for that hypothesis. the only resistance to be offered by this system would be if the hop-up made a very good seal and the bb required significant force to push its way thru the hop bucking and travel down the barrel. so in essence the back-pressure from bb to piston could only come from the hop system and no place else. so depending how good you hop-up is will determine pressures.

Interesting thread Max... but irregardless isn't a word, dammit! ;-P

Nic

So, you are saying it's non-irregardless? Lol

Touche Midget. I hate it when ppl invent new words without regard for perfectly good words.

I guess you don't accept my comparison of the amount of time it would take to accelerate a bb to a final muzzle velocity vs. they ROF that a mechbox achieves.

I showed how a 900shot per minute AEG would take roughly 5x more time to get the sector gear to come around to catch the piston again in comparison to the time it takes for a bb accelerated to 330fps to leave the barrel. I assert that semi or full auto mode does not have anything to do with "barrel suck" and that if such a phenomenon exists it is due to an insufficient amount of air compressed in a firing cycle. If the effective cylinder volume is less than the internal volume of the barrel + leakage losses then the bb cannot be pushed out the barrel without a reduction in pressure below atmospheric pressure.

I can confirm this effect with a piezo impact transducer I've designed for the testing of a novel piston head I'm working on. I have observed a significant difference in impact level from dryfire with no barrel ass'y, dryfire in an assembled AEG, and firing a pellet. The notion of impact reduction when shooting a pellet isn't too hard to confirm from the basis of thought experiment. If there is no place for energy to be absorbed (no pellet) all of the potential energy stored into the spring must be transferred to moving parts (kinetic energy in the piston and moving spring), movement of the very non dense air from the cylinder (so light it can't really absorb much energy), or heating of the air (cylinder exhaust can be a bit warm, but isn't that hot). With the air unable to absorb much energy relative to the very heavy piston and spring, all of the energy is transferred to the moving parts and must be finally dissapated by the mechbox.

If you fire with a bb, you present a restriction in airflow which means that some work is done on the pellet (a good outlet for potential energy from the spring). If your AEG worked on a 0% efficiency factor, then the bb presents no sizable backpressure and you have a very poor energy transfer i.e. then the bb would have a negligible effect.

DRY FIRE FATIGUE:

I've looked up aluminium fatigue cycle behavior tables and found that a 25% reduction in peak load can roughly account for a 10x improvement in cycle life of cast aluminum parts. I can measure a very large difference betwen dryfire and non dryfire impact (60% higher when dryfiring). Exceptional loads initiate cracks which sharply reduce fatigue cycle life. I strongly suspect that dryfire is the primary cause for initiating V2 mechbox failure.

The hop bucking applies it's resistance for a very short distance so it can't absorb a significant amount of work. Work is defined as force x distance. Hop up detent force is not very high and the distance applied is only millimetres.

If a bb trip time in a barrel is 0.00685s (see earlier post), then an accelleration to 330fps in such a short time equates to:

330fps~100m/s (I don't think in imperial unitized forces very well)

Acceleration = 100m/s / 0.00685s = 14598 m/s^2

force = mA = 0.0002kg * 14598 m/s^2 = 2.919 kgm/s^2 [Newtons]

This correlates to roughly 0.297kgf (div by 9.81N/kgf)

If a constant acceleration persists during the bb trip time, you have roughly 300g of force pushing the bb down the barrel.

If the cylinder has a diameter of 25mm (roughly right I think) and the barrel has a dia of 6mm, you have a pressure reduction setup (kind of like reverse hydraulics) which has force divided by the ratio of the AREAS of the two bores. That means that the force on the piston is 25^2/6^2 of the force on the bb (neglecting oring friction or bb-barrel friction). That means that the force on the piston is 17.36x higher on the piston than the barrel.

F(piston) = 0.297kgf * 17.36 = 5.156kgf?!

Actually, this isn't too unreasonable for a steady force. I just crunched a SP120 spring on a bathroom scale to about fully cocked length. The scale reads around 12kgf. The force at preloaded length is about 3kgf. If the spring is linear (it really isn't when the tight winds start to stack up), you get a average force of 7.5kgf.

COOL!

Then I can deduce that an AEG is actually a pretty efficient device. An SP120 is supposed to blast out at 0.2g pellets at around 420fps with an average piston force around 7.5kgf. Then an AEG firing at 330fps should be using a spring about 330^2/330^2 less average force (1/1.6) which results in an average force of 5kgf. Pellet energy is related to the square of speed. Piston travel distance is the same so only the force can change to affect work done.

Lower than the 5.165kgf I calculated above, but still reasonably close considering the crudeness of my measuring equipment. I would surmise that an AEG is pretty efficient at transferring spring energy to a pellet then (nearly 100%!).

my comparison of "relative" force exerted would be a man with a 200 lb of force on a sledge hammer hitting a 1lb weight. would the energy of that impact have an effect on the hammer or would it nearly all go to the weight with litttle effect on the hammer. this is a simple suposition based on mass and energy differences. if a bb weighs 200 times less that a piston and we ignore pressure differences it just doesn't seem right to me. i still think that for the fraction of a second that the hop seal allows pressure to build up in the piston to bb volume may itself be enough to start the piston decelerating and the net energy from the expansion of this volume is what propels the bb, adding to it the expansion of remaining air in the cylinder as the piston impacts the cylinder head. your numbers bear out some things for sure. my understanding of what you're saying is that energy must go somewhere and if no bb is present then it must be going only into the mechbox. my thinking is that some energy goes to moving air down the barrel (bb present or not) and that energy dissipated by the mechbox is always going to be significant. also, did you test with hop on full to off to see if that makes a difference, just for intersts sake?

Your analogy between a hammer striking a floating object doesn't hold because the interaction time between the hammer and the object is so short (collision really). In the case of an AEG, the piston is pneumatically coupled to the bb for a significant time. In a sense, the piston is connected via a nonlinear spring to the pellet because air is compressible.

The point of making the piston area so much larger than the barrel area is to acheive a good pneumatic coupling between the bb and the piston. Because the bb is a small diameter compared to the piston, you have a force division, a kind of pneumatic leverage if you will. It's related to the ratio of the square of the cross sections involved.

Consider this: if you put a 6mm piston in the barrel and it was well sealed to the piston, a 5kg force on the piston could be stopped with a dinky 0.288kg force on the little piston.

In the case of the bb, the little piston is allowed to move, the applied 0.288kgf force causes an acceleration of the piston.

As to hop up consideration, I only take velocity measurements with the hop up turned off. Hop up affects muzzle velocity in ways which may be difficult to recreate so I remove it from the list of sources of error. In any case, hop up reduces muzzle velocity, possibly because of increased barrel friction.


How about this for a closed system energy discussion:

If a 330fps spring exerts an average force of 5kgf (49.05N)

A piston travels roughly 46mm = 0.046m

Work done on the piston cranking it back and stored as potential energy:

force * distance = 49.05N * 0.046m =2.26J

Kinetic energy in a 0.2g bb moving 330fps (100m/s)

KE = 1/2mV^2 = 1/2 (0.0002kg) (100m/s)^2 = 1J

So the AEG in question would only be 44% efficient which doesn't really agree with my last post. I think I see a hole in my earlier reasoning. I did work out the piston force correctly, but there is no consideration of piston travel which means that there could be a significant amount of over compression to compensate for leakages, friction, and a reliability factor to assure against barrel suck.

In any case, 1J is not negligible in comparison to a total spring energy of 2.26J.

i'm just playing the devil's advocate here, but i can blow a .2g bb to about 200 fps down a stock tm m4 barrel. the maximum pressure my cheeks can hold is 2.10 psi. a quick burst from my mouth is much less than this about 1 psi. the volume of my burts is at best probably no more than 3, but probably 2 aeg full cylinder volumes. to reach 400 fps, my kinetic energy would need to be 4 times what 1 psi could create. there is alot of probablies here and no hard measurements, but you understand my line of reasoning here. i'm very certain that an aeg piston produces pressure orders of magnitude above 4 psi, far in excess of the volume difference between my mouth and an aeg cylinder. don't get me wrong, i'm not trying to poke holes in your reasoning or math, but something just doesn't sit right with me. if i provoke you to re-think something, which leads to another thought or idea on something, don't we all win?

Well, you're poking holes with no data or quantitative reasoning. The value is kind of limited. I'm not using any rocket science in my analysis. It's mostly highschool level physics f=ma stuff that most airsofters should be able to particapate with.

What chrony are you using to spit bbs? I can only get 32.9m/s with my optoelectronic chrony (109.5fps).

1psi equates to only 0.0199kgf ~ 0.195N. For a 380mm barrel, that's only 0.07J which works out to 26.45m/s which isn't far off from my 32.9m/s chrony result.

it's one of those dual ir photocell jobs. cost 80 bucks from wgc. it belongs to one of our team members. the chrony doesn't lie. guns i've measured with it here were accurate in other cities with other chrony's. but psi at what volume? volume of air to expand = potential energy and said expansion = kinetic energy. more volume=more energy. basic premise behind gunpowder and bullet velocity, right. i do realize that i have no data to present nor do i care to spend time and energy to get any. my thinking is just on the simple mechanics of what occurs and you disregard things that i've brought up because it doesn't fit you're mathematical model. unless you have star trek sensors placed at every point in the aeg to measure stresses, your math is just a little more sophisticated supposition, but it is just that, supposition. the point is unless you employ high speed cameras to every point from spring guide to flashider and see absolutely everything that occurs, we don't really know do we? we only suppose and sometimes the math works and sometimes not (out of your keyboard from a previous post). but if we don't discuss like rational people then ideas are not exchanged and progress does not occur. i'm not saying i'm right and you're wrong. you may very well be correct and i may very well be wrong, but in the end it's not really that important of an issue for me so if i'm wrong i can live with it. all i'm saying is that from my "empircal only" standpoint it doesn't sit right with me.

Well, I modified a mechbox so I can measure the impact against the cylinder head with a peizo transducer.

At 1psi, volume doesn't matter. You can only acheive a certain force (pressure x area) which corresponds to a certain amount of work done (force x distance) which provides an amount of energy imparted when you apply the force over the barrel length (I use 380mm in my calcs). From that, you can work out an fps with E = 1/2 mV^2

On the practical side, I did spit a bb thru a chrony with a brass barrel. I use a Guarder opto chrony which is pretty accurate. It agrees with my other opto chrony which I use for outdoor use (indoor fluo lamps mess it up). I got a speed of 32.9m/s.

I measured the force on the spring at fully compressed and standby length to determine avg force. From that I can determine spring energy. With a final bb velocity I can determine projectile energy.

It doesn't take sensors everywhere. It only takes careful observation and application of high school physics which actually does apply. Kind of like measuring the fuel intake of a vehicle and looking up the table value for the energy content of the fuel. Measure the torque and rpm of at the wheel with a dynomometer and you can determine the total mechanical efficiency of your vehicle which includes transmission losses.

An empirical standpoint is a supposition drawn from actual measurements. A theoretical hypothesis is a mathematical analysis. If you don't use either, you are using intuition.

Hehe, speaking of spitting BBs, Foxtail and Test_Tube used a TM loading rod and the field Chrony one day, got upwards of 300fps using .2g BBs. I've always found that putting your tongue on the opening and rapidly removing it yields blistering velocities (made a blow gun two years ago, 5/8" tubing, made some darts out of maple dowel, burned the tip and sharpened, was able to punch them through 1/4" 3ply birch plywood from across the basement, talk about straw in a tornado, eh?).

Assume maybe the rapid compression from using the tongue is on par with what Carl has said about the sudden compression that happens with a ported cylinder. Instead of an increase in pressure, it is just a sudden "POP!"

Admittedly Max, I haven’t done a great deal of Physics in a while. The one thing that I do recall though is that experimental error can be calculated by:

Error = (Experimental Value – True Value) / True Value X 100 = Percent Error

Using your calculated value of 26.45 m/s as your Calculated True Value and 32.9 m/s as your Experimental Value; your Experimental Error is almost 25%.
This is quite high for Experimental Error.

After you do your experimenting and collect your data you still need to determine your accuracy and precision in the experiment. Accuracy is how close you get to the target (True Value = Experimental Value = Bullseye); precision is how many times you hit the target in the same spot (repeatability).

If this value of 32.9 m/s isn't taken from just one reading of the chrono, I'd say your experiment has high precision but you should modify your experiment (which may not be possible) to increase your accuracy. Experimental error below 20% and in the range of 10 - 14 % is more acceptable.

Keep fightin' the good fight. :salute:

I recenty took my SR16 (frankengun) and was doing some experimenting of my own.

1 - Full cylinder with a 509mm barrel was shooting at 392 FPS.
2 - I replaced the M16 barel with a stock M4 barrel and the FPS dropped to 375.
3- I recently bought a silencer to replace my homemade silencer that was covering the M16 barrel, it turns out the new silencer was about 22mm short and I hade to cut the barrel. After all was done the gun now shoots at 396 FPS. Which means a 487mm barrel is better matched to a full cylinder than a 509mm barrel, thus making better use of all of the air in the cylinder.

You could put a 300% spring in your gun, however if your cylinder and barrel are mis-matched (same volumetric space, cylinder and barrel) you loose alot of air pressure and may end up shooting 320 FPS and doing major damage to your mech box, When using a full cylinder and short barel (piston slamming with lots of force, due to no back pressure, for no reason).

The oposite would happen with a ported cylinder and a long barrel. Not enough air volume to maintain the push on the BB to the end of the barrel, would result in friction between the BB and barrel as it exits, slowing the BB before exiting the barel.

So in my opinion and tests, before you do any upgrades, make sure your barrel and cylinder are matched as closely as possible, as the spring only effects how much pressure is exerted (higher air velocity), not how much air is actualy expelled. Expelled air is determined by the cylinder size itself. Ideally the piston should strike the clinder head a nano-second before the BB exits the barrel.

Sorry if this was already covered.

I wasn't actually trying to match my chrony result with a calculated result in that foray.

I just approached mcG's problem from two ends. Firstly by determining the theoretical velocity one could obtain from a 1psi set of lungs and zero barrel friction (assuming 380mm barrel).

The fps measurement I took was to see if 1psi lungs are in the ballpark of lung shot bbs. You can't really say there's any degree of experimental error between the two analysis since they do not use related inputs. I didn't measure the pressure I developed and calculate with that result so there really isn't any reason that the two results should agree. I used 1psi as quoted by mcG.

I understand now what it is your demonstrating, Max. I glazed over the part where you were actually “spitting” the bb down the barrel. So I guess 25% accuracy on lungpower isn’t too bad at all, unless you feel you’ve been inhaling to many metal shavings on a daily basis. I really shouldn’t try to comprehend things before my 10th coffee of the day.

My questions for you are:

If the volume of a barrel/silencer combination is matched to the volume of the cylinder, am I limited to always using the silencer? If for some reason I remove the silencer will the cylinder head slam into the bottom of the cylinder at a greater velocity from the lack of backpressure because the bb leaves the end of the barrel before the end of the cylinder head stroke? Will this cause damage? Is this at all a consideration?

the silencer has nothing to do with it...

it's the inner barrel length you're taking into consideration.

If you're asking what happens what happens if you remove the silencer and shorten the inner barrel length, then I suggest reading the very first post again where it was stated that yes, the piston head will slam into the cylinder head with greater force.

interesting
for the longest time I wanted to put a 250mm silencer on my SR16 and drop in a PSG1 tightbore but was worried about the suction effect. There wasnt much info regarding this thus far. And judging for Dirty Deeds last post about the SR16 with the M16 barrel, its a good thing I didnt. Ill prolly hold off untill we come-up with a barrel-length to cylinder matching guide.
awsome info

Here is the silencer I purchased.

King Arms OPS Model 3rd MBS Silencer ( 230mm )
http://www.wgcshop.com/pcart/shopper..._cat_Silencers

Here's your guide:

For a PSG-1 inner barrel (590mm, NOT 650mm!), you will need one of these cylinders:
- Systema Type-0
- KM Long
All of these are capable of handling up to 590mm inner barrels.
The information is all available in the product specs. If ppl are really interested, I can compile data for all brands.

If you're looking to do the 650mm inner barrel, you'll need to upgrade to a Systema bore-up Type-0 cylinder kit (which means new piston head, new cylinder, new cylinder head and new air nozzle) and you should be using at LEAST an M120 spring to get it working properly.

Okay, since I need a hardcore break from work, I've compiled the list:


Guarder Cylinder ( GE-03-01 ) G3 / M16A2 / AK
Guarder Cylinder ( GE-03-02 ) M4A1 / SR16
Guarder Cylinder ( GE-03-03 ) MP5A Series and SD Series
Guarder Cylinder ( GE-03-04 ) MP5K / PDW

Systema N-B Cylinder Type-0 ( ZS-04-16 ) M16A1 / VN / A2 / G3 / SG550 / AUG
Systema N-B Cylinder Type-1 ( ZS-04-17 ) AK47 / XM177 / SG551
Systema N-B Cylinder Type-2 ( ZS-04-18 ) MP5A4 / A5 / SD5 / SD6 / MC51
Systema N-B Cylinder Type-3 ( ZS-04-19 ) PDW
Systema N-B Cylinder Type-4 ( ZS-04-20 ) MP5K

KM TN Coated Inner Taper Cylinder for Long AEGs ( AEGS10 ) 400mm - 590mm
KM TN Coated Inner Taper Cylinder for Middle AEGs ( AEGS09 ) 200mm - 400mm
KM TN Coated Inner Taper Cylinder for Shorty AEGs ( AEGS08 ) <200mm

Prometheus Stainless Hard Cylinder ( A ) 451 - 550mm
Prometheus Stainless Hard Cylinder ( B ) 401 - 450mm
Prometheus Stainless Hard Cylinder ( C ) 301 - 400mm
Prometheus Stainless Hard Cylinder ( D ) 251 - 300mm
Prometheus Stainless Hard Cylinder ( E ) 201 - 250mm
Prometheus Stainless Hard Cylinder ( F ) 110 - 200mm


Not all guns are listed on there (especially for the brands which go by gun series and not inner barrel length), but you can derive which cylinder you want to use based on how Tokyo Marui uses same cylinders across different guns.

Full - AK47 / AK47S / M16A1 / M16A2 / M16VN / Sig550 / G3A3 / G3A4 / G3-SG1 / Steyr AUG
1/3 - G36C / M1A1 Thompson / Sig551 / M4A1 / M4A1 RIS / M4 S-System / SR16 / XM133 / CAR15 / M733 Commando
3/5 - MC51 / G3 SAS / AK Beita Spetsnaz / MP5A4 / MP5A5 / MP5 RAS / MP5SD5 / MP5SD6 / MP5-J / P90 / P90 TR / Sig552
1/2 - MP5K / PDW
^^ The numbers I used here indicate the placement of the port on the cylinder.

If anybody else knows of any other Marui AEGs which use version 2, 3 & 6 gearbox cylinders that aren't on that list and knows which category it goes in, let me know so that I can compile it to the list.

M14 and PSG-1 cylinders are unique to their gearbox. I don't know about Famas and Uzi. Anybody know?

so for these new cylinders, I should be able to pop out my old one and drop in one of these? or do I need to change the cylinder-head/piston head to match?

oh, and when i look at systema parts, whats the deal with these "area 1000" parts? how would they differ from a regular systema part?

Do you know how these work? WGC pictures don't show the ports for the middle and shorty aegs. All you can see are markings that look like rings around the cylinder.

Yes, you should be able to change JUST the cylinder, everything else will fit like it should.

Yeah, it's a direct drop-in. The bores are similar to Marui, so nothing else needs to be swapped.

Area 1000 is Systema's "budget/economical" line. The build quality and feature sets are equivalent to Guarder. Standard Systema are usually built with better materials and finished a bit nicer.


Yup, I do know how they work. I have them in all four of my AEGs. Like the name says, they are "taper" cylinders... so in other words, they don't use a port for ventilation. Rather, the interior is tapered, so it acts like a funnel. The piston entrance end has a wider bore than the end with the cylinder head. Depending on whether you get the shorty, middle or long cylinder, that will indicate where the end of the taper will stop. Essentially, it acts like a funnel up until where the "port" on other cylinders would end, at which point, the bore is at full close. I find it's a much more elegant solution than porting as the surface has less drag that can be applied to the o-ring. I've also noticed in tests that these cylinders seem to be just slightly more consistent than any other cylinder.

The rings simply indicate which version of the cylinder you have in your hands.
No rings = shorty
2 rings = medium
3 rings = long

Oh I see. Thanks for the info :)

Since this thread contains some really good info, including Illusions list of cylinder to barrel matching, can it get stickied?

I bought a gun with a stock V2 mechbox with a stock TM 1/3 ported cylinder.

The gun came with a shorter than stock barrel however.

How can I figure out what the longest tight bore barrel is I can drive with that cylinder?

Just a simple (yah right! LOL) comparison of the volume of the barrel to the volume of the cylinder using the math in the last few pages?

Would this help? http://arniesairsoft.co.uk/?filnavn=...andbarrels.htm I don't think tightbore differs enough from stock barrel's bore to warrant separate considerations.

Well..according to that, I need an un-ported cylinder for a 509mm barrel.


SO I guess I just cover the port and I'm good to go...!

Thanks for the link Saint!

I don't recommend port covering. The inside cylinder wall around the port still leaves an open gap that allows air to escape around the o-ring as it passes though. It will be inefficient, and your performance will have a blip in it due to that gap.

With the cylinder you have now, you can put up to a 410mm inner barrel.

Upgrading the cylinder is more then worth it, I put a AK length(455mm) tightbore in my M4A1 and had a few shots with it before I got my hands on a M16 Type 0 cylinder, sure it shot nice, straight, ect. But after putting that cylinder in, I was amazed at the difference in overall sound performance from the gun, but the range boost, accuracy and most of all, shot consistancy. It is a worthwhile upgrade for the long run, with a longer then stock barrel.

Thanks guys. Great advice. I didn't realize how economical a new cylinder is.

I went with a Guarder non ported, a Prometheus 509mm 6.03 tightbore, and a Systema silent piston set. (Also upgraded the nozzle and tappet)

I was reading through this, and it got me thinking:

Would the way to find the perfect cylinder length (or even where to cut holes in a full cylinder to get a more efficient go) to do a simple volume analysis?

That is, you'd want the same volume (not mass - it's constant no matter the pressure) both right before compression starts and the bb is still at the start of the barrel, and when the piston has reached the end and the bb is just about to leave the barrel?


That said, Mcguyver, on Semi I believe that you would still get some vacuum suck back if your cylinder wasn't matched with your barrel. Because as the BB travels down the barrel, the mass of air inbetween it and the piston head does not change. (assuming the piston is momentarily at rest) The volume however is changing, resulting in a forced expansion of air beyond a pressure of one atmosphere, creating a back pressure. (again, only if your cylinder and barrel length aren't matched (cylinder too short for your barrel length)).

I could be wrong, as I'm not fully learned in the whole cycle the AEG goes through, and the timing of when everything happens.

Using a tight-bore would mean you could get away with a smaller cylinder, correct? (technically speaking, though the effects may be negligable)


Basically what i'm saying is this: Say you have a 450mm 6.02 barrel (assuming the bb is waiting for the compression right at beggining of the barrel). That means that your barrel has 12.8 cubic cm's of volume, so, right before the piston head begins compression, you'd want 12.8 cubic cm's of volume between the bb and your piston head.

Am I right or wrong in my thinking?

In a perfect world... in a perfect system, your theory is 100% correct.

But we don't live in a perfect world, and the AEG system isn't perfect. The air seals within the compression chamber are not 100% efficient, so all of the following areas of air loss must either be corrected to get your formula to work, OR you must allow a greater volume of air to compensate for the lost air:

1) piston head to cylinder wall
2) cylinder wall to cylinder head
3) cylinder head to air nozzle
4) air nozzle to hop up rubber
5) air nozzle to BB
6) BB to inner barrel wall

Variances in temperature can also affect the demanded and supplied volumes of air due to expansion of materials, as well as the quality of compression (stiffening of o-ring rubbers in cold, etc)

Easiest way to go about all this? Just get the pre-manufactured cylinder sets out there. Less headaches, and would work out to a better finished product... and probably even cheaper than any of us could produce. All the R&D is already done... why re-invent the wheel?

Because I'm bored and distractions are welcome. Even if they're difficult. It's what I do. Lol, in all seriousness though, I was never thinking I'd use that to make myself a cylinder or anything, I'm not that cheap. Plus, in first year engineering, everything is a perfect system:mrgreen:.

If you get bored with all this stuff, try designing an audio speaker box. Lots of math to play with there, but the bottom line is if it doesn't leak, it will work satisfactorily.

I have an M4 that I ported the living crap out of before I even knew why this was done. I figured it let the cyl fill faster and reduced "suck-back"...
I just measured a CA cyl at the shop and matched dimensions, adding a few more holes further back, tapering in size. So there are three holes in a row, largest one at the start of the power stroke. There are four of the hole groups going around the cyl. The porting effect is as amplified as it gets in this gun. This gun has a high-speed Systema motor, 170 spring, metal bearing spring guide, metal bushings, reinforced piston/head, and a Stainless steel cushioned cyl head.
How does this gun work? Terrible on semi. The bb will go about two feet before dropping. On full auto, yeehaw! It will spit a solid stream of hard-hitting pellets with very acceptable accuracy for CQB.
I was building a short gun anyway, but I have since learned that putting a long barrel with this gearbox results in a dog of a gun with lousy range.
http://www.air-sharp.com/KillSAW2.jpg
http://www.air-sharp.com/KillSAW3.jpg
http://www.air-sharp.com/KillSAW4.jpg

Holy Frankengun! Don't think I've ever seen a gun as customized as that.

What exactly does unported mean?
 

When you say "unported cylinder" are you refering to the fact that the cylinder isn't made / modified to the specifications of that specific model of gun?

It means the cylinder has no ports in it at all. It's a straight tube instead of one with an oval opening near one end.

Sorry if this is a stupid question, but when you swap out your cylinder to allow for the installation of a longer inner-barrel, do you have to replace the cylinder with the original one if you were to replace the barrel with the shorter one, or will the new cylinder work properly with any length up to what it's designed for?

If you're using a short inner barrel with a cylinder meant for a longer inner barrel, you subject your gearbox to more stress (projectile has long since left the barrel, and thus, there is no longer any backpressure on the piston head to reduce impact on the gearbox), ROF is slowed down, and velocities are typically not as high nor as consistent.

so I have been thinking. If a barrel of a particular length only takes so much volume of air to work properly, would a Cylinder bore up kit then have a negative effect on performance. Or has changing the displacement been thought of, and the position of the port on cylinder been moved accordingly?

Like Ilusion just posted, if the cylinder is too big for the barrel, the piston will have no BB left to push out the barrel (it will have already left) and the piston will slam into the cylinder head.

well yes I understand that, maybe I just did not ask my question right. If I have say an M4 style gun, w/t the proper cylinder, what is the point of getting a cylinder bore up kit. since all that will do is create more air displacement, which really is not needed. and will then create the piston having no resistance at the end of its stroke.
I guess you could solve this by shortening the stroke of the piston. but that is probably not worth it.
so bore up kits I guess are they a worthwhile investment, or just a waist of money.

They are only a good investment if you get an extended barrel.
For example, if you put a suppressor on that M4, and put in an extended barrel that extends to the end (or just before the end somewhere) of the suppressor.

Bore Up kits are generally used for longer than normal barrel lengths, or for high velocity setups.

Pneumatic efficiencies are much more glaringly apparent above 400fps with exponentially higher air losses when shooting with an M120 or higher. Thus, bore up kits are sometimes suggested as a way to reclaim lost air volume passing through the inner barrel at these higher velocities.

As a side note, bore-up kits should only be used with M120+ springs - I'd recommend you begin considering it once you step in to M130 territory. Springs weaker than that may not have the strength to expand the o-ring enough during the compression phase.

Sorry I think this was answered earlier in the post in like 2005 but I just want to make sure that the cylinder in my JG M4A1 is the same as the one in my TM MP5 SD/6 so I could put the M4 barrel in the MP5 and vise verse without any adverse effects.
Then I could put M4 barrel in Mp5sd with a direct silencer attachment an outer barrel extension and a flash hider and make a I don't know what to call it a custom MP5 carbine frankengun thing.

Due to a recent piston havok, I'm in need of a new cylinder (VERY bad luck!). After looking around I decided to go for a cheap Area 1000 cylinder. It's only for a JG 552 anyway, and it might happen again :D Anyways I noticed that the venting port on both my P90 cylinders, and my SIG 552 cylinder has the same placement as the Area 1000 cylinder for the MP5A4/A5/SD5/SD6. I also checked some other brands, and the pictures all suggested that the MP5A4/A5/SD5/SD6 actually has the same venting port placement as the MP5s listed, while the M4, SR-16, XM177, SG551 etc. has it's port slightly closer to the back. My JG 552 and Echo1 P90 gearboxes both have longer vents, while my TM P90 cylinder is shorter (like the Area 1000 one). As far as I understand, what really matters is where the vent port actually ends, and the piston head starts pushing air. Maybe the 1/3 and 3/5 categories needs a little rearranging? Can you confirm/unconfirm this?

When that's said I have to thank you for the countless times I've found your posts with much needed knowledge! I consider you one of the best airsoft gurus out there!

PS. I hear that Famas uses the same kind of cylinders as v2, v3 and v6, or maybe it's the other way around ;)

Yeah the idea of the post is to limit compression to roughly the volume needed for the barrel length. The main idea, AFAIK, is to prevent the piston from slamming forward without resistance (like dry firing) because the BB left the barrel during the first 1/3 or 1/2 of the piston stroke.

As far as the FAMAS, the cylinder is different from V2/V3. If I recall correctly, it's slightly shorter (a few millimeters).

When checking closer here, I discovered that the length of the inner barrel on the MP5s in debate, are 229mm long. In other words pretty close to the P90, SIG 552 ++ barrel length of 247mm. MC-51 barrel is 285mm long while M4A1 etc. are 363mm long. I would guess that the pictures might actually be correct (I first thought they weren't, as can sometimes be the case), and that the P90, SIG 552, etc. should be in the same category as the MP5s. I would still like some1 to confirm this, as I don't have any ones myself to compare against.

I am tempted to simply put a piece of tape over the port on the cylinder and compare FPS before and after.

I feel so much extra air escape throught the port when the piston moves forward that I think it causes most of my FPS loss!

If you have the right cylinder for your gun then no, it's working correctly.

As Styrak said, it's not about how much air that get's vented, but if the barrel and and cylinder are matched or not.

Well, I can't offer anything but empirical evidence. Just 10 minutes ago I did this to two of my G36s.

JG G36C: Stock Ported Cylinder - Shooting 360 FPS reliably. I taped over the cylinder port and now it shoots 387 FPS.

CA G36K: Classic Army Upgrade Cylinder set for G36. - Shooting 400 FPS reliably. I taped over the cylinder port and 5 minutes later, now it shoots 436 FPS every single time.

I've just gained 30-40 FPS on two different guns made by two different manufacturers using both a stock and upgrade cylinder both made for the guns that they went into.

taping the port should technically offer very little or no positive benefits whatsoever. There is still the gap between the inner wall and the outer wall where air can pass through as the o-ring passes the port.

Although compression would begin at the very start of the stroke, as soon as the o-ring reaches the start of the port, the seal would be compromised until the o-ring reaches the end of the port.

There may be other effects happening, such as the piston starting the launch of the projectile - followed by a break in projectile acceleration as the piston head reaches the port, causing the piston to accelerate to an even faster speed so that as the seal is closed at the end of the port, it will finish off the compression cycle to launch the projectile at a higher speed.

I would not recommend this as a permanent modification. The o-ring passing by the tape repeatedly may eventually smear adhesive on to the o-ring and across the inner wall of the cylinder.

I'm not very clear on all these mechanisms in action but I can tell you for certain that before I covered up these ports, I could feel a lot of air being blown out of the port on each cycle as the piston moved forward. Despite whatever has occured, I've improved the efficiency of my guns and the amount of air moving through it by taping over the port and having less escape on each compression. I don't know whats happening. All I have is results and I tested this thoroughly. I chrono'd 30 bbs before and 30 bbs afterwards (well within 10 minutes as taping the port is easy) and the gain is a reliable 30-40 FPS without question.

I wasn't dumb enough to put the adhesive side on the inside. I have another piece of tape in between with a smooth surface facing the inside of the cylinder.

And you guns have stock inner barrels?

I'm not doubting your results. All I'm stating is that this is not recommended as a permanant modification, but your results are interesting. Of course you will feel air blowing out of the uncovered port... it's there to expend "unnecessary" air volume prior to the actual compression cycle.

They are both stock lengths but the C has a Prometheus 6.03 and the K has a Madbull Black Python 6.03.

I did more testing - interesting results. I took out the m130 spring from the CA36K which was shooting 400 prior to taping and then 436 afterwards. I then put in the stock CA spring. The gun went to shooting ~320 FPS. I taped it again, and still ~320 FPS. So taping on a weaker spring has no discernable effect. I'm guessing that with the more powerful spring the compression cycle is forcing out too much "uneccessary" air before the piston head fully passes the port. With a weaker spring, it makes no difference.

Normally, I don't think many would expect any noticeable FPS increase, but there can be explanations for that. Maybe your cylinders are matched to the barrel lengths very close to the cylinder limit, thus giving it a speed gain when a little more air is compressed?

Gees!!! These info are really making me think how much math is involve in making more effective parts, now I know why some stuff cost so freaking much for a piece of metal!

But I have a question here, not sure if it's answered or not(kind of skip here and there). Here goes:

Does a m16 length(509mm?) inner barrel need a cylinder with no port to match that length of barrel?

If so, let say the stock barrel is 6.08mm in diameter, what would happen if I upgrade it to a tightbore(6.03mm) of the same length? Do I need a cylinder with port now because of the smaller air gap between the bb and the barrel?

If so, instead of changing a ported cylinder, would it be the same to increase the length of the barrel to maybe 590mm to match the cylinder??


The next part if you don't get it's fine to skip it, this jsut kind of help me understand the whole thing but with simple number.
The point of this is to make this a simple and easy math, and not use stuff like a lot of symbols and such so hear me out.
Let say my gearbox produce a 10 push force(10PF) with port.
And gear box with no port produce 15 PF.
Let say it only takes 7PF to move the bb and keep it moving.
For every 6 inch it require 1 more PF to continue moving the bb down a 10mm(diameter) barrel.
For every 6 inch it requires .5 PF to continue moving the bb down a 5mm barrel.

So here's some question:
A) Is it true that it require less PF to move a bb through a smaller(in diameter) barrel(10mm to a 5mm)?

B) In this situation(T/F), the perfect length with a ported cylinder and 10mm diameter barrel would be 12"?

C) In this situation(T/F), the perfect length with a ported cylinder and a 5mm diameter barrel would be 36"?

D) Is it true that cylinder with no more produce more PF?

E) I have a non-ported cylinder with a 12" long barrel, does it match? If not what would happen?


Thanks.
F) I have a ported cylinder with a 36" long barrel, does it match? If not what would happen?

Yes

Yes, it is still recommended to still use an unported cylinder. The cylinder porting is not that precise and there is quite a wide tolerance margin taken in to consideration with the recommendations.

By increasing to a 590mm inner barrel, it is recommended to upgrade to a bore up unported cylinder.

True

I suppose, but you are not taking in to account other (external) forces. Hence, why such a wide margin of tolerance is considered in the recommendations.

False. See above. Also, the area of force applied to the surface of a spherical object does not change linearly as you have indicated. See some of the formulas in the earlier part of this thread.

English what?

Are you referring to your imaginary scenario or real world?

In any case, why are you concerned about a non-realistic scenario? Why not just stick with what's tried and proven?

See above.

Because I was hoping you would explain it in really simple English...


What does "bore up unported cylinder" mean?... There's different types of unported cylinders?!?!... Also, what does it mean when people say a cylinder is "oversized"?

Is there somewhere were I could read about them?...

Thanks for answering ILLusion, that really help me understand the fundamental of airsoft's gearbox.

Yes, there are different types of cylinders. Standard cylinders and bore up cylinders. Bore up cylinders have thinner walls, which allow for greater air volume (and thus, a larger cylinder head stem, larger air nozzle, and a larger piston head to make up for the larger surface area that needs to be covered.)

Cork gun vs. AEG
 

Having just joined this forum I am total captivated by these very technical discussions. I find them very helpful in rounding out my own knowledge and experience.

Even though MadMax started this thread back in 2005 I was drawn to his explanation of bb size compared to piston head size.

I’m sure we all remember as a child receiving a popgun (perhaps better named a cork gun) for Christmas where the Piston Head was approximately equal in diameter to the size of the cork. Well, we all know how far the cork ranged thus I believe offers a good empirical proof of MadMax’s theory.

So I did some math calculations and I found some interesting results. I wanted to see if bore-up cylinders were really necessary for long barrels like thePSG-1 (650mm). The volume of a barrel using the equation for the volume of a cylinder V=pi*((d/2)^2)*l, where d is 6.05mm and l is 650mm. I found the volume to be 18685 cubic mm. I then took measurements of an AEG cylinder (check me if my measurements are wrong), and I found the diameter to be 24mm and the length to be 72mm. Using the same equation above, I found a cylinder's volume to be 32572 cubic mm. That means a type-0 no hole cylinder has 175% the volume of the longest barrel on the market. This makes me question why bore-ups are necessary, considering their purpose is to increase the cylinder's volume to fit the barrel. However, I understand the entire volume of the cylinder is not used because the piston head and cylinder head take up some room inside the cylinder. I also understand that aeg's are not 100% efficient. This still doesn't justify to me the need for a bore-up cylinder when it's volume is 75% more than the barrel. Cylinder volume should not be an issue even with these considerations.

Keep in mind, among other things, that you're compressing that air quite a bit to get the BB going fast, the pressure in the barrel right before the BB leaves the barrel is quite above atmospheric pressure I imagine.



Disclaimer, this statement is an educated guess.

Many people have done your same calculation and have come to the same conclusion, however:

1) You are not factoring in the "dead" volume of air between the piston head and the tip of the nozzle (when extended) where it touches the BB.

2) You are also assuming a perfect system with zero air loss due to air seal inefficiencies. A lot of air is lost due to such inefficiency. Losses occur around the piston head, the cylinder head, the connection between the cylinder head and air seal nozzle, between the nozzle and BB, and finally, air escaping around the BB as it travels through the barrel.

Your assumptions are only theoretical, but practice shows that in real world scenarios, bore up cylinders ARE required for barrel lengths that long.

Go for it then...and when you end up with a 200fps rifle, try a bore up kit.

Also doesn't take into account the variables created by full auto fire.

Though I feel a little bad about bumping the topic again, I am curious about an aspect of cylinder and nozzle design, and am hoping someone can set me straight.

I understand the ported/unported, volume matching, and loss characteristics of the cylinders discussed in this topic, but I was wondering why nozzles are not pressure sensitive. That is to say, when the piston comes forward, it ejects a bit of air through the port (if there is a port) to help acceleration and create a more aggressive pressure curve. If this is the reasoning, then why are nozzles not designed with a pressure-sensitive valve designed to snap open at the right time, dumping pressurized air faster than the piston is capable? Would that not create an even more aggressive curve (as pressure waves travel at the speed of sound) than letting the low-pressure air push the BB down the barrel for the first couple of inches? Or would you have pressure loss around the BB greater than the effect of a slower acceleration as it tries to overcome inertia?

Thanks for your time,
Melon

The mechanics and engineering aspect of getting something reliable would cost an arm and a leg to buy. Plus, having an extra moving part, inside the nozzle, would wreak havoc in your gun in the event it breaks.

Also, where would you put said valve? The nozzle already sits pretty deep on the cylinder head. Anything inside would be incredibly small and impossible to fix. How would it 'snap' closed? Spring loaded or a total redesign of something that works. What if it jams closed? You'd end up with a back pressure that could possible aide in stripping your piston and gears. How good can a valve be to work fast enough for full auto?

In the end, the amount of air lost is insignificant. IMO, you will lose more air leaking down the feed tube then you would gain.

Good point(s). I guess there's a point at which reliability greatly outweighs the need for a slight performance increase. Besides, people have no trouble hitting field FPS caps anyway, so why add something when it would be useless?

I'm not saying it's useless but at this point it's not practical. the costs of trying to perfect something reliable would exceed the potential gains. current cost for a reliable nozzle is < $10. I can't imagine how much someone would charge for a valved nozzle. I can see what you're thinking but just it's not feasible.

I recently sent my MP5 into a local store for repair. I put a Madbull 6.03 363mm tbb in it, and so I asked about changing the cylinder to an M4 cylinder while they were in my mechbox, and the guys there said that they find the best results with Type 0 cylinders in all guns. So thats what I ended up putting in my gun. Ill let you guys know what the results are when I get my gun back in a couple weeks.