Nothing too brittle or it won't be able to handle the rifling. Draxxus Nightmare worked well, but it was around two months old.
Accuracy, Range, and Sound. See description.
The barrel doesn't clean itself out as well as advertised, but still reasonably good.
Even with bad paint i was seeing improved accuracy and not to mention range! My range increased by around twenty feet! Those of you who have ever tried longballing someone and been only hitting around their feet will appreciate this. Another thing, the wind seemed to have less of an influence on the flight of the ball, flying straighter than my J&J polished bore when i shot them right after each other. This barrel really helps with sound too, it might seem louder when you are behind the gun, but is much quieter if you are the target. The reverse porting actually directs the sound back towards the shooter as opposed to the shoot-ee. I broke two balls and the only response from the barrel was every couple balls would zing off to the side and my grouping got bigger by 5 or 6 inches.
I would personally recommend everyone else stay away from this barrel so that I'm the only one out there with it. Seriously though, it's a great barrel and i love the shroud with the rails.