the best mod in my opinion for the bolt is the shocktech delrin.
low pressure is accomplished by getting your gun high flowing inside and then regulating it w/ a regulator.
low pressure is better for a few reasons
1. gun is more gas efficient
2. gun shoots more accurate
3. less ball breaks
4. velocity is more stable
and there are many more reasons
a good site to buy a shocktech delrin from is www.paintballgear.com