In a normal firing sequence, the slide/barrel assembly back up .100 inch and the bullet exits. At .200 inch, the upper barrel lugs are completely disengaged. At .250 inch, the barrel is on the frame bed.
Let all that sink in.
If there's a disconnect malfunction that allows the pistol to fire .100 inch out of battery, the lugs are still engaged horizontally and the slide and barrel are still tied together. Another .100 inch, the bullet exits and pressure drops. This may damage the upper barrel lugs, but it won't bulge or blow a case.
If the disconnect malfunction allows the hammer to fall between .130 and .200 inch out of battery, the hammer face can't reach the firing pin because it will be stopped at the junction of the center rail and the bottom of the firing pin stop.
If you are getting bulging cases, they are coming from something else.
Check closely to see if the slide is cracked at the top of the ejection port on the left side. If it's there, the crack will be about 1/8th inch forward of the breechface, adjacent to the small breechface guide block. This is where most of them crack, and sometimes they're hard to detect.
The crack will extend about a quarter-inch if it's recently happened...more if it's been there for a while. If you've ever noticed a feeling like fine grains of sand hitting you in the face...the crack is very likely there.
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