contrary1

Looking for some input. Have a supernova that we picked up last fall but didn't get to use much until this spring. Trap season rolled around and one of my boys has been shooting with it (it fits him great and I may never get it back). The only problem is that we keep getting split (and singed around the crack) hulls back out of it. The splits range 3/8" to 3/4" long on the plastic a little above the brass. Usually it is on one side, but on occassion two sides. This is happening on reloads (don't shoot any factory loads here). The loads are a target load (1170 fps) in good hulls. It was splitting STS hulls (many once fired) and thinking it was some weak hulls did some old style AA hulls that split as well. Roughly 1 in 25 will split. Interestingly, we run the same loads and shells through a remington, a weatherby, and a mossberg as well and none split in those guns. They just split in the supernova. I checked the chamber on it with a T gauge and it is .815 (a couple of thousands larger than the other three shotguns) but don't imagine .002-.003" is causing the splits....or is it? Any thoughts or ideas?