I've fired some stuff over the years and bulged cases mean one of these in my experience:
High pressure rounds (usually milsurp),you have the answer for this one.
The timing is off;the bolt is cycling rearward too soon,accuracy and velocity are good indicators of this. Check springs,rods,etc. I have an M1 I built with a short barrel. Extra power springs cycle too fast to strip rounds from the clip but extract perfectly.
The chamber is too large;again milsurp related,gun has been shot out,rebarrled/rebored. The rounds fit the chamber,but when fired there is too much space around the case and it bulges. If the gun cycles properly in this case the brass will get stuck in the chamber. If the cycle is off it will extract case and the brass will bulge. YMMV