When I sort through brass, and find pieces that have that bulge, I run those separately through a single station sizer. I look the result over carefully. Most of the time, they end up fine. I do toss a few.
It's a serious HEADSPACE issue that causes that to happen.
As the round is fired, the brass jumps instantly to the back of the gun, exposing the sides of the brass to little or no support. In theory, it should happen to every shot fired (should be consistant brass markings).
---------- excerpted from an on line article on the subject------------------
Headspace checking:
Semi-Automatic Pistols. Semi-autos need to be checked for barrel lockup before gauging. With the slide in battery, take careful note (or a photograph) of exactly where the slide is aligned with some point on the frame (or how far the barrel engages in the ejection port). Then remove the extractor and recoil assembly from the slide. The gauge is chambered and the slide is gently pushed forward until it stops. The slide/barrel should return to the exact same position with a go gauge. The slide/barrel should stop somewhere short of fully in battery with a no-go.
Living with headspace:
Semi-auto pistols chambered for straight-walled cartridges can usually live with somewhat long chambers. Unless it's a target pistol, it's likely that no one will ever notice an excessive headspace condition on most of these pistols. An extreme case of this condition would be when someone decides it's a good idea to try shooting some .40 S&W ammo through a 10mm pistol. I've seen it done more than once, and the pistols all worked fine. According to SAAMI specs, the maximum length of a 10mm chamber is 1.004 inch, with the minimum length of a .40 S&W case being 0.840. This represents a theoretical 0.164-inch excessive headspace problem! However, as long as the round in the chamber is held in place by the pistol's extractor, it fires and sometimes shoots reasonably well. Is this dumb? Of course; it's never smart to intentionally chamber and fire ammo other than what the arm was manufactured to use.
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The .40 S+W/10mm thing demonstrates where the issue someones gets amplified. It has to do with the max length of the brass, since the front edge of the brass is where the pistol round is supposed to be up against the chamber lip.
Suggestion: If you are taper crimping the bullet too tightly, it's possible that rounds are chambering deeper than they might otherwise. That leaves more space behind the round, unsupported. Over time, the gun's extractor takes the beating, the brass gets bulged, and since the gun cycles, you just live with it. Try backing off on the taper crimp. The test for a tight enough taper crimp is to fire the gun with the muzzle just a few feet from a clean sheet of paper. If it leaves a spiral spray around the bullet hole, it's too loose. When the spiral spray goes away, it's just right. And, semi auto's should not get roll crimped. That takes away too much of the needed case length. Remember, the semi's are headspaced on the front end of the case mouth.
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