Most are field adjustable so they can be tuned to field rules. If you build your darts right, you will have next to no blowby, that will increase power. I would try to find a way to prevent the bolt from blowing back, this will increase power by a lot, so you shouldnt lose much if any velocity using a heavier projectile. This should be able to be done with little work, I've got an old marker, I'll see if I have enough parts to illustrate.