Gees, I though that this thread would die after the Chuck Noris bit, but NO!
Where to start...
First off, a paintball barrel is no more accurate then a piece of pvc. The main factor is the ID of the pipe. The closer inner diameter to paint diameter match, the more efficienct and accurate the gun is. Ideally the paintball will only contact the barrel at its seam, yet not allow much air past. I will try to find the best match at HomeDepot, either 1/2" sdr, 120sch 3/4, or 3/4 cpvc. As for "extra range" with an Apex, I plan to make my own (see first post pic). The material the barrel is made of (ie friction) only slightly affects efficiency. The advantages are that it is cheap, I can make it the best length for max efficiency, I can attach a silencer, hop up, and whatever other do-dads I want.
I do not EXPECT the gun to reach 20 bps, but it is definatly possible. The limiting factor, like most of you said, is air flow. The 1.5" bolt case could be increased to 2". None of the numbers in the plan are set in stone, just put to get a relative idea. I am shooting for 12 bps with the current design. I may use a home made external reg IN addition to the on board one. The purpose of this it I want to be able to ajust the velocity (and range) without having to fumble around with the remote CO2 tank on my back.
As for the "automatic sniper" paintball is played by "accuracy by volume", and always will be. Because the liquid and capsule spin at different rates, after about 150 yd (on most guns) paintballs will usually gyrate out of countrol. I designed this valve/mag setup to cover many fields of play. The components could easily be switched out os the "sniper" case and into a "assult rifle" case. The performance would be the same, of course, but it could be more compact. Who wants to be stuck with a super accurate, big, slow sniper in close-quarters combat? Or an assult rifle at 200 yds in a thick forest? Do you want victory with a Jack-of-all-trades or realism and defeat?
Also, I an starting to lean toward using a QEV. Congrats, you may have discoraged me

. Still, how would I pilot the valve while still maintaining a constant sorce of air? I plan to route the pilot air to the mag, so that the pressure is maintained, possibly eliminating the piston.