i have a M16A4 with a V2 gearbox that im trying to lower the fps in.its currently shooting 426fps with .20g bbs,so i was going to pop a M120 spring in thinking that would do the trick,but to my suprise the spring already in the gearbox was shorter(26 coils)/M120(31 coils) & it seems like the spring already in has less tension then the M120.so with that being said,does any one know how i can get the fps down some? i would like it to be around 400fps,but no lower then 380fps.i have a cylinder with a hole in it(the one already in the gearbox has no hole),so i was thinking maybe that would take some of the air flow off,but other then that i have no idea.ide prefer to work with what i already have instead of having to buy new parts or cut coils off either springs(but if i have to i will cut some coils).any suggestions would be great.thanks

I would still try the M120 spring, after break in it should drop below 400.

yeah I would try that m120 and break it in and see what your shooting,also a different piston head or o-rings could lower it a bit.

Decreasing the volume of air in your cylinder can cause your BBs leaving your barrel slower but in a bad way. You could create a vacuum in your gun. You should change your spring. Any "120" spring besides those marked 120% would be fine. Springs are not all the same, tensions is not always determined in an amount of coils. If you absolutely do not want to buy another spring than you could cut coils off until you are at the velocity you want. Cut the coils that would be in you piston though. For $15, a new spring might be easier.

well i went ahead & put a different gearbox in that i had,verified to shoot 400-404fps(w/ .20g bbs) with about a 6.03-6.04mm inner barrel.my next question is how much do yall think the fps will increase with a 6.0mm inner barrel? i was think roughly around 10fps would be the most it could gain off of that,but if it does put it up about 10 more fps,ide still be shooting around 410-415fps,any ideas or 1st hand experiences on how much tighter barrels have increased fps?

but on another note,i do think im going to put that M120 spring in the gearbox i took out & see what its shooting next time im around a chrono.

Depends on the length, you might loose FPS. I would not use a 6.00 but I would not go over 469mm in a 6.01. Great for gas but not so much for springs.

Have you tried going to a heavier weight bb? Should be an easy way to drop the fps without making mods to the gun.

most fps regulations are based upon using a .2gram bb

allthough a heavier bb drops the overall fps...it carries more energy as well

If you are any more than 5 or 10fps over 400, you may be required to use your gun on semi only at some fields in AL. And was your MB cronoed using a TB? If not, then your fps with the TB could be up to 15fps higher than you think.

that cylinder with the hole in it could possibly lower your fps...but it could also cause u problems depending on the volume of your barrel