Heavy Valve spring and Light Main spring
with a combination of some internal work to boost that 12 efficiency.
Also you could:
Flasc 0.678 Bored barrel (9") they are like 35$ Sweet deal and will work for 95% of the paint you ever need, in a hotter environmental situation with swollen balls use the stock barrel
+ one of Alpha's sweet Silencers with a Clamp. Enjoy ninja Phantom with bad booty efficiency.