I agree on the Flasc barrel but the Lapco Bigshot 12" with Apex will also work. Accuracy is similar with both but the Flasc does allow you to change tips on the fly. Very useful when you get a break in the Apex during a game.
Whichever you choose, it can take a bit of fiddling around to get it installed so that when the barrel it tightened up, the shroud fits correctly. I loosely installed the barrel and screwed it into the BT, then when everything was lined up I put tiny bits of tape on the barrel showing the top and bottom, so that when I removed it to tighten everything up, I could easily see where it needed to sit.