CO2 power downgrade - anyone know how?

[straffham]

Recently got hold of the new CO2 powered Cybergun "Swiss Arms Protector" (ie Mini Uzi). It is a fantastic "grin factor" GBB gun, very solid, heavy, fast and loud, especially on full auto and shoots straight for a good 60m. However it is a little too "hot" to skirmish with at around 380FPS on 0.2g BB's.

Question is, is there a proven way of reducing the velocity on CO2 guns? The mechanism is essentially the same as a GBB pistol, with a floating valve which allows the shot to fire before the mechanism recoils in a heavy metal "bolt".

I was advised by someone who uses CO2 guns that drilling a 1mm hole through the air nozzle would do the trick as it would bleed some pressure off. However this has made negligable difference, and I don't want to end up with an air nozzle looking like swiss cheese as getting a replacement will probably be nigh on impossible.

Anyone know any surefire way of slightly reducing power to the BB but NOT affecting the blowback performance?

 

[TacMaster]

If you could get something like an NPAS for CO2 that would work. Out of curiosity, how much did drilling through the air nozzle reduce FPS?

 

[straffham]

About 5 FPS tops! I gradually drilled out from 0.5mm to 1.5mm with no appreciable difference, on opposite sides of the nozzle (I'm informed only drilling one side will make the BB curl in flight, something to do with the physics of gas flow through the nozzle). I had considered trimming a fraction off the HOP end of the nozzle to reduce the air seal but am loathe to do that except as a last resort.

 

[Samurai]

In gas guns you usually cut the hammer spring. I don't know the firing mechanism of the uzi but if it has a normal hammer spring then you can cut it a very little shorter. Be careful to cut only a little piece because it has a major effect on the fps.

 

[straffham]

cheers for that. I'd thought of looking at the hammer spring but my concerns would be that CO2 mag valves are under more pressure than a standard green gas valve so need a good "kick" to open them. Also even if it worked it would reduce gas to the blowback mechanism as well as to the BB so may not cycle as fast or even cycle fully at all?

However I have now sorted it by drilling 2 holes 1.6mm right through the air nozzle at 90 degrees to each other in an X when viewed from front of the bolt (on the wider part behind the air seal/neck that sits in the HOP chamber) which has made all the difference. This requires a full stripdown of the bolt to remove the air nozzle, and careful cleaning of the air nozzle to remove plastic swarf so I wouldn't recommend to anyone not familiar with working on GBB's.

Gun now fires around 330FPS so skirmish friendy, and the blowback is as good as it was before. Happy days!

I have become aware of a UK retailer who can sell the Mini Uzi pre downgraded to around 315FPS via a slightly more refined method than mine. Not sure on price. PM me for details in first instance and I'll put you in touch.

 

[PT247]

I know it is a completely different gun but the M700 has an adjustable hammer spring, just screw it in to tension (higher fps) and out to soften (lower fps), trimming your spring will lower the fps but like you say it could cause issues with the blowback. I imagine that if a GBB running green gas can cycle fine with lower fps and a metal slide I am sure softening the CO2 will still cycle ok..... Green gas runs at about 115psi where as CO2 is roughly 800psi (if google did me right?)