[incrediboy729]

I have a classic army m15a4 and here are all the parts i have installed (with an x for recently installed within the week):
G&P m160 motor x
12v elite mini wired to deans (was a 10.8v but i added a cell for extra power x)
Guarder m140 spring x
G&G Hyper torque helical gears x
Systema hopup bucking x
CA tightbore
So after all these are installed everything is fine and dandy with very high fps. After shooting it more the velocity goes down to the point where i cannot pierce the bottom of a soda can first shot 2 inches away. Shooting from a distance (20-25 yards) will either get me through one side or none. With a m140 i would assume my fps would be a bit more no? Is there something wrong? i have checked the internals since the fps loss and everything is fine, cylinder compression seems good. What do you guys think? piston head maybe? Much thanks in advance.
-Brett