m120 spring only putting out 300fps

[TheRev]

hey guys i have rebuilt an a&k sr25, ive done alot of guns but not an sr25. i have short stroked the piston by 3 teeth and have sealed it all properly, the only thing is i put in an ics m120 and im only getting 306 fps. i mean its consistent, every time. i just cant seem to work out why its so low. im aiming for 390 fps. ive never had an ics spring before so it could just be that i suppose??


any help on this would be amazing

cheers guys

[Skolob]

Re: m120 spring only putting out 300fps

Short stroking will remove power as the spring will not get to full compression. If the piston seal is good, along with the hop and nozzle then the answer is probably he short stroking. IIRC an M120 would get about 390 fps without short stroking.

[TheRev]

Re: m120 spring only putting out 300fps

i thought about that i had the original m120 in it before and it was doing 440ish, cant see it loosing 140fps??

and because of the sr25s have a longer cylinder the act of short stroking would make it the same as an m4, hence my confusion as if you put an m120 in an m4 it would do around 390

[Skolob]

Re: m120 spring only putting out 300fps

You aldo have to consider the accelleartion force when the spring is released, with short stoking you are gettin much less tension on the spring before release. I don't know what gn they base the m120 on, in tems of cylinder and barrel length.
If you have definitly got good air seals, and here is not blow by on the piston seal then the only thing really left is the short stoking. I could see short sproking loosing quite a lot of fps.
Check the nozzle is engaging properly with the hop, the hop rubber is good, teflon tape the rubber and see what happens after that.

[dadio]

Re: m120 spring only putting out 300fps

if you want to bring it up again you will need to put a spacer under the spring to pre compress it by the same length that the 3 teeth effectivly removed,this is the most likely reason you'v lost power not an air seal fault unless the hop rubber is too soft and its farting air passed the seal under the exess pressure but i doubt that as even soft hop rubbers are good for 350fps.

[Vector]

Re: m120 spring only putting out 300fps

The SR-25 uses a slightly longer spring hence the lower power. Try and buy an M120 spring for a PSG-1 and you should get the results your after.