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Complicated thinking: Why match cylinder porting and barrel length?

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Old April 16th, 2009, 20:18   #61
Corleone
 
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Quote:
Originally Posted by ILLusion View Post
Full - AK47 / AK47S / M16A1 / M16A2 / M16VN / Sig550 / G3A3 / G3A4 / G3-SG1 / Steyr AUG
1/3 - G36C / P90 / P90 TR / M1A1 Thompson / Sig551 / Sig552 / 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
1/2 - MP5K / PDW
^^ The numbers I used here indicate the placement of the port on the cylinder.

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

Last edited by Corleone; April 16th, 2009 at 20:27..
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Old April 16th, 2009, 20:51   #62
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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).
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Old April 19th, 2009, 13:55   #63
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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.
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Old May 1st, 2009, 20:19   #64
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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!
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Old May 1st, 2009, 20:37   #65
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Originally Posted by SNK View Post
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.
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Old May 2nd, 2009, 10:12   #66
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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!
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.
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Old May 2nd, 2009, 20:52   #67
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Originally Posted by Styrak View Post
If you have the right cylinder for your gun then no, it's working correctly.
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.
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Old May 2nd, 2009, 20:56   #68
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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.

Last edited by ILLusion; May 2nd, 2009 at 20:59..
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Old May 2nd, 2009, 21:03   #69
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Originally Posted by ILLusion View Post
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.
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Old May 2nd, 2009, 21:14   #70
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And you guns have stock inner barrels?
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Old May 2nd, 2009, 21:52   #71
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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.
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.
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Old May 3rd, 2009, 01:36   #72
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And you guns have stock inner barrels?
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.
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Old May 4th, 2009, 07:59   #73
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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?
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Old September 10th, 2009, 17:05   #74
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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?

Last edited by highny; September 10th, 2009 at 19:20..
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Old September 10th, 2009, 22:51   #75
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Quote:
Originally Posted by highny View Post
Does a m16 length(509mm?) inner barrel need a cylinder with no port to match that length of barrel?
Yes

Quote:
Originally Posted by highny View Post
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?
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.

Quote:
Originally Posted by highny View Post
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??
By increasing to a 590mm inner barrel, it is recommended to upgrade to a bore up unported cylinder.

Quote:
Originally Posted by highny View Post
A) Is it true that it require less PF to move a bb through a smaller(in diameter) barrel(10mm to a 5mm)?
True

Quote:
Originally Posted by highny View Post
B) In this situation(T/F), the perfect length with a ported cylinder and 10mm diameter barrel would be 12"?
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.

Quote:
Originally Posted by highny View Post
C) In this situation(T/F), the perfect length with a ported cylinder and a 5mm diameter barrel would be 36"?
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.

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Originally Posted by highny View Post
D) Is it true that cylinder with no more produce more PF?
English what?

Quote:
Originally Posted by highny View Post
E) I have a non-ported cylinder with a 12" long barrel, does it match? If not what would happen?
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?

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