I shoot a .40 Glock. This used to mean that the brass it ejected showed a bit of a bulge near the base. It also meant that the decapping/sizing die didn't always resize the brass completely, leaving a bit of the bulge behind. I have replaced my barrel with one from Lone Wolf, which works a treat. I recommend them. Go buy a barrel. Their barrels are made to somewhat more exacting specs than the factory barrels, which means that the cases must be sized all the way down to seat smoothly. Brass shot from the LW barrel is better supported, and doesn't show the bulge but other peoples brass, found at the range frequently needs a bit of help.
The method is to push the brass completely through the final sizing/crimp die before anything else. The problem is that some of those cases DO NOT want to go through that die, so I give them some help. First decap and preliminary size. Then drop the case into a final sizing die, mounted in a centrifugal press: