the best way to lower the fps on a sniper rifle would be to reduce the type of spring you are using. airsplat.com has a whole bunch to pick from to decide what type of FPS you're looking for.
The only way to decrease an airsoft fps is to buy larger grade pellets such as .25 gram. Otherwise, just buy a pistol with a lower fps.
go to an airsoft shop and ask for an fps reducer ther only like 25 bucks for a good one
I don't no about spring, but the Green Gas M700 Sniper Rifle Competition Professional Airsoft gun, has 720-FPS!!!! And the, Spring CSI L96 Bolt Action Airsoft Sniper Rifle, has 550-FPS. They are both from, Hobby Tron.com
go for the m14, unless its cheap looking.
Pain is relative.
Most of the guns listed here will shoot around 400 fps or above. http://www.6mmbb.com/servlet/the-Airsoft-Sniper-Rifles/Categories Expensive guns are around $300-$800.
Personally, I would get the Well MB01 L96 because it has better performance. It gets 500+ fps while the DE M50 gets about 315 - 325 fps. For a Sniper, you want a good fps to get better accuracy.
MB03 by well
350 or lower
upgraded JG BAR10, the gun comes stock around $110
Green gas or Propane. Green Gas offers lower fps and much more expensive for the price but Propane is alot cheaper and a lot more fps. Propane smells really bad though
Why the hell would you buy a 500fps ak47? The internals will be torn to bits unless they are like top of the line internals. But if you are going for the sniper position, I would go with the sniper. If you are caught mid-way and cant decide, A&K makes a 500fps Dragunov.
Depending on the distance 10 yards im sure 300fps fps will go through the can