Originally Posted by F106 Fan
I always thought of the bulge as a large ring entirely around the case. The entire chamber is too large.
OTOH, the pimple (or dimple or whatever) is a section of brass that is bulged out right where it meets the feedramp. There are plenty of example photos of brass failure in this region. The entire head doesn't separate, just a blown out area where the feedramp is overcut.
I realize this is kind of an old problem and it's been known for years and years. But it's strictly a .40 S&W Glock problem that, AFAIK, has since been corrected. Still, there are probably barrels around from the earlier versions.
I don't load .40 but if I ever do, it will be for a Sig 229.
Well I'm glad you cleared that up.
I also have an old Gen 2 G23 in .40 That never had a bulge of any size on it. For years I even did a couple of things with it that I didn't know you wern't supposed to do until I started reading on the internet.
And that was load lead in the factory barrel and they were 155gr lead swc to boot. They fed, fired, and ejected fine without any noteworthy leading or bulges or pimples or dimples.