Short barrel/new upper for Socom Gear M4.

[mcintosh]

I've been thinking about building a new upper for my Socom Gear Noveske M4.

The goal is to make a super short CQB gun that can utilize my current M4 mags. Hopefully the shorter barrel will also reduce my velocity to the point that I don't need to crack open my gearbox (it is unmolested, and I'd like to keep it that way.)

Being new to airsoft I have no idea what parts are compatible, or if the shorter barrel will have the desired effect.

Help would be appreciated. My google-fu is weak right now and I have come up with no useful info on my own.

[TheEnd]

You are on the right track that the shorter barrel will drop your FPS. The problem is that if your cylinder is drastically over volumed it will cause massive FPS loss and above average force on your shell. I'm not sure what you consider super short, but it sounds like you want something shorter than the standard 10.5" barrel. Some M4 AEG's come with full cylinders. If you try to use a 100mm barrel with a full cylinder your BB will leave the barrel before the piston has returned half way.

The piston builds speed as the main spring decompresses. Since your spring has only decompressed half way, you are losing a lot of force because your BB has left the barrel before your piston has reached its top speed. This means a 400 fps AEG (when using a 363mm barrel) with a drastically over volumed cylinder (using a 100mm barrel) could shoot in the low 150's (depending on BB weight, hop up amount, barrel bore, etc). Because your BB has left the barrel your piston is now moving air with no resistance. This means your piston will be slamming into the cylinder head with more force than normal, essentially "dry firing". Your muzzle report will be very loud, and your gearbox shell will most likely crack after extended use.

Long story short, it is not a good idea to use a super short barrel if your cylinder is over volumed. Before we can give you a barrel length to shoot for, we need to know three things.

1. Is your current cylinder ported? (Does it have a hole in it?)
2. If it has a hole, how far back in the cylinder is it placed?
3. What length barrel do you want to have on your new upper?

Once you answer those questions we can tell you if your plan will work or not. Your cylinder will most likely have too much volume for anything super short.

[mcintosh]

I would prefer the overall to be "super short", the barrel itself doesn't have to be 5" or something silly.
I'm glad to hear that shortening the barrel will have the desired effect. I'm still wondering where to get an upper that will fit my socom gear noveske lower. Are most of the uppers out there compatible, none of them?
I'm just really resisting something like an AK pistol or an MP5. Everybody and their little sister has an MP5.

Here is a pic of my piston

Last time I chronoed this gun it was shooting 313 with .25g bbs. I'm sure I'll be asked to chrono/play with .20g if I play indoor this winter, hence this build.

[Knief]

You know, in theory 313 FPS with .25g bbs is exactly equal to 350 FPS with .20 bbs, and heavier bbs often gain just a hair more energy than lighter bbs because they sit in the hop up chamber longer. Have you tried chronoing the gun with .20s? You might just sneak under the 350 FPS limit.

[Timm]

Try not to leave your spring compressed, and kneifs info should be spot on.

[mcintosh]

I'll get out the chrono and check once I get some .20s