Ok when i bought my mag a while back i asked what barrel system they would recommend and they said CP pro barrel kit and Ive been reading alot about barrels recently and stuff and AGD says an 8-10" back area is best for their guns. Then i found out about the Evil Pipe and theres all that good stuff about it. The smoothest barrel aorund, 30 degree angled porting but the back sizes are only 6". So i wanted to know how long the backs are for the CP barrel kit and which one would be better.