Spring Upgrade
 

I just recently upgraded the internals of my G&G M4 pneumatic blowback. I put in new gears, new piston+head, new cylinder head and a new S100+ spring. My friend told me that it should bring my FPS from what it was before I put the spring in (364FPS with 6.03mm, 363mm tightbore) to in the ball park of about 380FPS. When I chrono'd it with .2g ammo, it was firing about 334-344FPS with the S100+ spring. Everything is running smooth, found no air leaks. Only thing we though of that would decrease the FPS was the blowback. Anyone know if the blowback could really drop my velocity that much?
Thanks!

the G&G blowbacks are prone to decreased velocities due to the Pneumatic blowback feeding directly off of the cylinder. i've owned a few of them and it's a normal side effect of the gun. now that said i'm not sure if 40FPS is a normal drop. i didn't chrono the difference when i plugged the blowback feature. (small piece of electrical tape means i could remove it later if i like)

APS guns have a blowback feature that runs off the gear system meaning no loss in pressure BUT they work of the gears so unless you chip the trigger it could be open/partial/closed whenever yo stop firing.

Wow, thanks, I was gonna order a new cylinder to lose the blowback, but I'd have never thought of the tape, I already have some so it'll cost me nothing! Thanks a tonne for the help!

Alright so I put the tape, it worked a bit; it's now shooting 354FPS, which is what it was doing with all stock internals...Still not firing 380 like it's supposed to be doing...

354fps is still totally usable and you won't see any difference to a 380fps gun. Be happy it didn't drop to 230fps.

The s100 shouldnt get you to 380 need to use a s110

S100 should be shooting about 370fps with a good airseal. S110 would be 410fps.

http://www.airsoftparts.ca/news/modifyspringtest.pdf

Hey there,
Using this guide you can see that the m110 will put you around 390 on average.

http://www.airsoftcanada.com/SpringChart.php

Best of luck.