Getting a gun to shoot <300 FPS?

[ThunderCactus]

+1, that chart is as accurate as can be!
If you compare with ehobby's own spring ratings, they're 50-100fps UNDER what the spring is capable of at it's best.

[CDN_Stalker]

I just tend to hope for the math route, hoping the rating is actually meters per second, add on the rough increases of a tightbore, bearing spring guide, and ballpark it. Of course, seems different manufacturers have different concepts on how long a meter is, in which case, the above spring chart gives an idea of what one might expect when comparing an untried spring compared to a known one.

[m102404]

A M90 or 100% spring should work. Try to avoid cutting down springs as it's very much less than exact.

Since a tightbore, bearing spring guide, bearing piston head and how nicely the internals are setup will all tend to boost your FPS a bit you can hedge your bets a bit and if your m90 spring is a non linear spring (i.e. a Modify sp90 has closer packed coils on one end) you can reverse the spring and put the tighter pack at the front closer to the piston head. That will kill off some FPS as I've regularly seen a sp90 spring hit 340fps in a nicely tuned setup.

As always...a chrony is the only way to know for sure. And the peace of mind of doing that many guns....and then then powering them back up afterwards...will pay for a cost of a chrony right there.

[cetane]

My lil m4* shoots a solid 350 with a modify 90 spring in it. With a 100 it gets to shy of 400. I've seen m85 springs. That might do it?

* (g&g m4 cqd w/cqbr 6.04 barrel stock internals except for piston head & viton rubber o-ring)