With a tiny high intensity white light about the size of a big wooden kitchen match stick, I could get right into the chambers and the "ring" I was seeing when I'd look through the barrels at a light, was the beginning of the forcing cone that had a different surface coloration than the chamber walls themselves. The skinny high intensity light also allowed me to get the 6" machinist's rule right in there with excellent visibility and the chambers measure 2&5/8" to the edge of the different colored area at the front edge of the chambers.
Taking another once fired Win-AA hull, I flattened the edges of the fold marks of the crimp with a pair of flat-billed pliers so the sides of the hull continued right on up straight to the top of the crimp section. I then fully packed the hull with #9 shot, wrapped a piece of heavy cellophane packing tape around the top half of the hull with an inch sticking up past the top, then folded that excess down / across the shot like you'd fold the end of a coin wrapper.
Holding the barrels in one hand with the extractors relaxed in and flush, the fully extended shell slid right in all the way each time, with light even pressure the whole way...I was looking to see if there would be a possible increase in pressure during that last quarter of an inch or so but could not detect any change...there was light, even drag the whole way in...and mind you with probably an additional .020" thickness to the hull dimension from the packing tape wrapped around it. So based on all the above, it appears that normal, plastic, .12ga star crimped 2&3/4" shells should be fine.
Ordered some barrel hones...hope to have this thing ready in a few weeks and I'll post some pics...thanks again for the advice & counsel.
