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shrapnel_85

how much to shave...

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Right im currently running a pretty much standard internals in my gearbox apart from poly piston + bearing spring/piston guides on what I believe is a m90 spring that came with the gun. (ca Sig 552)

With this and a 7.4 30c Lipo on dean's I'm getting a constant 330fps with an rof of 16rps.

 

I am wanting to up my rof to around 25 max but would like to maintain or even up the fps to 350 but without getting a bigger battery. I know I will need to short stroke the piston a bit but I wanted to know roughly how much would I need to on a 14 tooth piston? As I wanted to upgrade to a m110 spring. Obviously a high torque motor will be required also 😊

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To me, that looks like an M100 spring - 100m/s is 328fps

 

Just shim it right, get a new motor and you'll be away. 20rps isn't hard to achieve at all. Something can usually be deemed 'broken or in need of attention' if the rifle is firing under 10-15rps

 

Certainly don't need to short stroke anything.

 

also, you won't gain anything for upping the fps by 20

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Before the I had the new spring/piston guide I was only getting 300fps and 13rps with 8.4v nimh.

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To me, that looks like an M100 spring - 100m/s is 328fps

If only it were that simple! Most manufacturers these days must rate their spring with .25g or something because I know very little companies that have M100 that shoot at one joule. The variance of air seal between guns is probs another factor with another major one being barrel length and and barrel bore.

 

In theory it should work out as an M100 is a 1J spring. Here in Northern Ireland the legal limit is 1J but everyone I know uses an M90 and those with upgraded DMR length rifles need an M85.

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Just as Dave says, a general service, shimmed, AoE corrected and 2nd tooth on piston filed down and a new motor should be all you need.

 

I wouldn't bother with an upgraded spring, but you could just wack in an M100 and that should bring it to near 350 fps.

 

All the best!

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