Did your barrel somehow escape the factory without being rifled? Seems like you should be doing better than that.

Only thing I can thik of is a scope/mount problem, if you are shooting with a scope that is. If the scope is mounted correctly, and is holding its zero, it has to be ammo or barrel related. You tried a bunch of ammo, so it is starting to sound like the barrel. You didn't buy this thing to get the kind of performance you can get from a smoothbore with rifled slugs, so let T/C know what's up. In my experience, they will take care of you. If you ship the barrel to them, they will check it out.

Oh, is it mating to the gun properly? Does it have any more playthan your other barrels?