Just wondering if barrel movement under recoil could be the cause of some drum failures? Less than perfect inletting around the breech plug, and just shooting, would let the barrel move a little more and more over time, and that 'perfect fitting' cutout in the lockplate would just keep stressing the breechplug at it weakest point. I wonder if a little fore-and-aft clearance between, but with support underneath would be better than a tight fit if the barrel starts to move under recoil? Of course, if everything is tight so there's no movement at all, would be the better solution.