Bear in mind also that by ironing out said bulge you are altering the diameter of the bullet that's inside the case too. That displaced material has to go somewhere, and if the bulge is on one side and not the other it means the bullet is cockeyed so if that's the case by "busting the bulge" you're either shrinking the diameter of the bullet or crushing it mis-shapen, neither of which will do accuracy any good. Best to suss out why they're bulged rather than mashing the bulges.
Could be also that your brass isn't compatible with your bullet in terms of wall thickness and/or where the internal tapering begins, in relation to where the base of the bullet falls internally. Can't speak to .380 brass and bullets though, it's been 40 years since I messed with loading for one. I can speak to this phenomenon regarding .38 Special brass and wadcutter bullets though and am merely wondering if some permutation of the same formula is happening here. I would mic the wall thickness(es) and determine if your bullet bases are intruding into the internal taper.
