Brass that has been fired twice and only neck sized won't rechamber. It hangs up where the case seperation occurs which is almost at the datum line (just ahead of the belt)
Each time I resize the brass a few thou is shaved off of the brass just above the belt. All the way around the case. The area shaved is probably 1/4" in with.
After reloading and shooting and resizing the brass 4-6 times I can begin to see a thin dent in the brass. This where the seperation occurs. I 'll get some pics of the brass that has been shaved.
I'm going to try and go to the range and do some shooting. Then just resize the neck and get a better idea of why the brass bulging at the base. Start over and see what shakes out.