If it is any help, I have a Thompson Center Black Diamond XR with the longer barrel of course. As long as you shoot loose powder those #11 caps will fire the charge off just fine. Also the Black Diamond is a great shooting rifle. It will shoot sabots as well as conicals. At least mine will. What many forget is the Black Diamond was considered at one time the best Thompson Center inline rifle for many years. Then along came the Omega with the different style breech and the Black Diamond has kind of went its own direction.

I have a Knight Wolverine with the short 22" barrel, so if barrel length is causing you concern, don't let it bother you. It is a great shooting rifle also.....