So I opened my first mechbox...

[grantmac]

It's a Ver.2 rear-wired.
I opened it to get an idea of how it was supposed to look, install a MOSFET and see how it works. So far nothing too difficult to get my head around (I've rebuilt motors and built non-SMD electronics before). Pretty cool little piece of machinery and the previous owner/maintainer really put great parts into it.

I do have a couple of questions. Mainly about performance and airseal:
1) The nozzle to cylinderhead connection seems like it would be fairly leaky, is there a way of sealing it better?
2) Should I remove any piston teeth? I've seen pistons with the last tooth removed. It's a full cylinder with an M4 length barrel. I'd like a bit better trigger response.
3) Air-tool oil is the prefered lubricant for all compression parts right?

Thanks,
Grant

[Styrak]

Airsoft cylinder grease is the preferred option for compression parts. It's a light grease. You could also use light silicone oil if you don't have any.

Yeah the cylinder head to nozzle connection can be leaky. Best best is to get an nozzle with a good o-ring inside it like a Deep Fire or Modify.

[Drake]

1) The nozzle will sometimes be "leaky" (depends on the brands of all the parts) when fully pushed on since that's the position it would be in when the piston is moving backwards (spring being compressed). Note how the nozzle is attached to the tappet plate and how the sector gear will push it backwards during the initial part of the cycle. When pulled forward (where it would sit when the tappet plate is in the forward position) the seal should be better.

Some nozzles have o-rings on the inside which provide a better seal. But all in all you probably lose more compression in the area between the nozzle and the hopup unit.

2) Some people remove the last piston tooth. I never felt the need to. Maybe someone else can provide an argument for it, but personally I wouldn't advise it (unless you want to short stroke the piston).

3) Dunno. I use teflon grease. It's worked fine for the past 10 years.

[grantmac]

Alright, last question then.

A spring with progressive windings (I believe usually known as irregular pitch) is installed with the tighter coils on the spring guide right? Because this one had them in the piston, which to me would lead to more weight moving and so reduced efficiency.
Thanks,
Grant

[The Saint]

Originally Posted by grantmac

2) Should I remove any piston teeth? I've seen pistons with the last tooth removed. It's a full cylinder with an M4 length barrel. I'd like a bit better trigger response.

No, if you've only just opened your first mechbox, it's not recommended that you start tinkering with the piston teeth. If you're looking for better trigger response, a better battery is a simpler method.

Also, if you're using a M4 length barrel (363mm), you're really better off getting a 3/4 or 4/5 ported cylinder.

Yes, tighter coils to the rear.

[m102404]

I pretty much went with the white lithium grease that comes in a tube. Lasts for about a dozen+ mechboxes or until you lose the tube...I usually misplace the tube by then and end up with a new one.

Just use enough to lightly coat any surface that rubs/interfaces with another...the last one I cleaned out was packed with grease (looked like vaseline actually). It took 4 diaper wipes to get it all out (they're great and will clean up just about anything).

Remember...any excess grease that's between the piston head and the cylinder head (and any in the nozzle) is going to end up being blown through your hopup and down your barrel. It'll mess up your shots for a bit and if it's really bad you'll end up taking your hopup apart to clean it out.

Unless you're going for a high speed setup where the sector/half-gear might come around for the next shot before the piston is all the way forward...I personally don't think that you need to remove the first tooth or shave down the second tooth. What spring are you using? The lighter the spring and the faster the setup (gear ratio, motor type, battery size) the more risk you run of crashing the piston and sector gear.

Swapping different cylinder heads and nozzles will eventually give you a combo that has a nice seal. I test with the nozzle forward...just far enough so that the rings on it are just behind the end of the cylinder head. That's about where it's going to be when it fires. If it leaks there I usually look for a better setup. If it's a really minor slow leak...it's probably ok.

Some air seal nozzles that have an o-ring don't seem to seal up nicely either. Use a really tiny pick or screwdriver to flick out the o-ring...lube it up a bit and reinstall it. It should seal up better.

Have fun and best of luck with it.

[grantmac]

Thanks for the responses.

I compression tested the cylinder with the nozzle forward and I'm satisfied that it's sealing sufficiently. It has an O-ring so I can scratch that off the to be upgraded list.

The reason behind the whole thing (MOSFET) was for faster response. Currently running a 120 spring with 18:1 gears (standard I believe). Trigger response is good, but I'm a big fan of best in all ways. I will be playing around with pre-cocking once I get my head around the code.

So far the only grease I'm using is white lithium. I keep it in a syringe for doing really tiny gears in RC servos, I applied is sparingly. I don't think I'll need to lube anything else as the previous owner did a thorough but not excessive job when he sold it.

I realize that a ported cylinder would probably perform better, I will either go with a longer barrel or new cylinder eventually. Is this why I'm seeing 380fps with a 120 spring?
Thanks,
Grant

[Styrak]

That seems about right for a 120 on an M4. My AUG shoots about 390 or 400 or so with a PSG barrel and M120 spring.

[m102404]

On single shot you shouldn't get any "suck back" unless the gears are over spinning and going into another rotation.

If your mosfet has active braking it should be arresting the motor very quickly/consistently after the cut-off lever cuts power.

If you're getting one FPS reading between single shot and a lower one on a burst of full auto...you might be getting suck back.

A couple of other factors that'll affect FPS (assuming that your compression is solid and consistent).
1. Tightbore. std bores are 6.08mm. clones can be all over the place up to 6.10mm. good old stn tightbore is 6.04mm. lately I've been running 6.03mm. They'll bump your fps a bit (maybe up to 10fps?...depends on so many other things).

2. Nozzle to hopup rubber seal. If you look closely at a bunch different "M4" nozzles...you'll notice that some have rounded noses, others have angular edges and some look almost square. How tightly the nozzle seals up when it's in the hopup unit and pressed up against the lips of the hopup rubber will affect the final FPS. How consistently it does it affects accuracy.

3. Leave your hopup all the way off when testing. In fact, check down the barrel from the chamber end to ensure that the rubber isn't protrudin into the barrel at all. When you play, it'll be on. But if you're testing changes for FPS differences...turn it off and eliminate it as a variable. No hopup will result in the highest FPS you'll get all other things equal.

4. Bearing spring guide. If you have one, the bearing and thrust plates stack will pre-compress your spring a bit and you'll end up with higher velocities (vs. a regular spring guide). If you have ones that fit...you can simulate it with washers. +10-15fps

5. Bearing piston head. Similar to a bearing spring guide. But be cautious that if you have too much "stuff" (i.e. bearing stacks on both ends) you may run out of room to physically compress all the spring coils together and it'll jam (or worse strip). I've used Modify springs for the long last while with zero issues. Some springs (Guarder comes to mind) use really thick wire. Thick wire, lots of coils, precompressing with bearings on both ends...trouble.

6. Hopup unit. Now, I haven't been able to confirm this one...but some say that a one piece metal hopup unit will seal up better than a plastic one. Maybe due to flex...I don't know. Also, there's plenty of concensus that a one piece hopup will seal up better than a two piece hopup. I'm not sure about that...but again I haven't tested it or really dug into this one. I run King Arms Enhanced Hopups or G&P Hopups...both have worked well for me.

[grantmac]

Currently running the following:
Bearing Spring guide
Systema Silent cylinder head
Systema bear piston head
One piece metal hop-up

No binding at all, gun runs smooth and quiet.
It's really, really consistant (last crono was 380 +- 2) except it occasionally over or under hops the BB. I think it's running too soft of a hop-up rubber because I just barely have to turn it on. I think I will switch to either a Prom hard or KH65 in the next while unless there is something better out there and a Prom barrel when I've got the cash.

I'm mainly just trying to make sure my overall set-up is as optimized as possible.
Thanks,
Grant

[m102404]

If it's shooting 380 +/- 2 don't touch it. Smart guys would be really happy with that.

Personally...I'd keep fiddling (never been very smart). When you get your different rubbers, try mixing up the hard/soft nubs with the different rubbers.

You could also teflon tape the houp rubber and barrel before putting it in the hopup unit.

Also, if you're handy, you could buy a really long barrel and lop off about an inch at a time and recrown the end.

If you're going to mess about barrels and hopups a lot...don't use the KA Enhanced...once you get the barrel retaining clip on it's a bugger to take on and put on again without messing it up.

Have fun...post your results/observations.

[Skladfin]

Originally Posted by grantmac

Currently running the following:
Bearing Spring guide
Systema Silent cylinder head
Systema bear piston head
One piece metal hop-up

No binding at all, gun runs smooth and quiet.
It's really, really consistant (last crono was 380 +- 2) except it occasionally over or under hops the BB. I think it's running too soft of a hop-up rubber because I just barely have to turn it on. I think I will switch to either a Prom hard or KH65 in the next while unless there is something better out there and a Prom barrel when I've got the cash.

I'm mainly just trying to make sure my overall set-up is as optimized as possible.
Thanks,
Grant

KM hop up rubbers have a very short lip, it will give you horrible airseal problem because of that. For me, I lost 70FPS just from changing to KM RH75 hop up rubber.

Also, the Prometheus hard has a rediculously tight lip, it WILL cause jam problems on just about any hop up unit. The only hop up unit that it worked well, from what I have seen, was only stock TM plastic hop up unit.

Moreover, a softer hop up rubber will provide less hop effect than a harder one would with the same amount of setting.

My reccomendation for a good hop up rubber would be systema or prom soft

[grantmac]

What is the teflon tape for? Have you got any experience with the MadBull shark buckings?

Interesting, almost everything I've read has been oposite to your experiences Skladfin. Especially with the RH65, it seems to be regarded as universally awesome by most.
I would think that a softer hop-up would create more spin because of the increased friction.
Most of the time hard rubbers are recommended for guns over 350, something about them lasting a lot longer and being more consistant.

Thanks,
Grant

[Skladfin]

I'll take a pic of what I mean, about the RH75 rubbers. Yes, the accuracy was fucking insane, the shots all went SO straight I thought it was a joke. If I didn't lose so much range(because of the 70FPS I lost), I would have kept using it.

Harder ones gives more hop, I speak from experience.

[m102404]

I've always gone with either a Guarder black hopup rubber or a Guarder clear for the last 20 or so rifles. They both seem to work well...in rifles from 280-420. The Guarder clear went into my KA FAL Carbine (396fps)...and that fixed things up with flyers and shrinking up the groups quite a bit. Hopup is barely on...which preserves as much velocity as possible. Guarder blacks in my M4 rifles...they're shooting 380fps.

A prometheus hard (red) didn't work in 3 AEGs (caused jamming) and sat in the parts bin for about 2 months. I put it into my L96 (600fps) but haven't seen how it shoots at distance.

I bought a couple of MB Sharks (black) and they didn't work at all in 3 different rifles (I think they were all shooting 380-400)

My thinking was that the hopup rubber hardness was supposed to be matched to the FPS/power of the rifle. Soft for stock stuff...harder for high velocities. Hard rubbers won't grip sufficiently at low velocities...soft rubbers get torn up at high velocities.

Well...I just go with what works. Guarder black 95% of the time, Guarder clear the other 4.9% of the time. I tear into my rifles so often (70% of the time they're probably disassembled) that checking the hopup and swapping the rubber out if it's worn isn't a big deal. Rubbers are cheap. I buy 6+ at a time. I probably haven't "had" to change out the rubbers on any of my rifles yet...but they usually end up changed out just while I'm fiddling with them.

As I said before...smart guys would be happy with a consistently shooting rifle (i.e. use whatever rubber gives the most consistent hop)...but I've never been very smart about things and can't leave well enough alone.