What is causing this ridge on bullet seating?

[Longshot4]

Since bullet base is bulging case. The bullet in the case is tighter than designed. The force to release the bullet when fired would increase. I suspect pressure could or would spike. If it were me I would pull the bullets. Resize and find a bullet with the proper length. Quit dreaming of making a more powerful 380.

Im one of those guys that likes to get a little more out of my loads. That solid cooper design bullet comes in odd weights. Same with my 44Mag.

be safe pull the bullets.

 

[mikejonestkd]

As others have mentioned above- its just cosmetic. I have seen it quite often, especially with heavy for cartridge bullets since they tend to be fairly long. You are just pushing the bullet into the section of the case where the brass is a bit thicker.
Load and shoot as long as they chamber OK.

 

[Nathan]

What causes the ring? Sizing die? Seating die? Crimping die? What brand/type is it? Or is it the gun causing the ring?

Based on your words, I’m not certain.

Some have proposed this could increase pressure? Why? The seating force did work on the bullet and/or brass to create this ring. There is likely little pressure left. Other things might cause pressure, but I don’t see how the ring does.

I have shot a lot of rounds with a ring like this after a full investigation into the cause. It was always my Lee Factory Crimp Die so I sold those to people that wanted them.

 

[Unclenick]

All bullets bulge a case a little. If the bulge gets too wide, the Lee Carbide Factor Crimp Die (CFCD) will rub the wide spot, marking it as the case passes through the carbide sizing ring, which is trying to ensure no cartridge is too wide to feed.

Cases designed for self-loading pistols typically have a tapered thickening of the brass below where bullet bases are supposed to stop in them. This thickening prevents an unsupported portion of the case, as some chambers leave exposed, from blowing out on firing.

If you seat a bullet past the point where the base is supposed to stop, it enters that thickened portion, bulging it out farther than the thinner brass does, and this forms an extra-wide bulge at the bullet base. Since that happens during seating, it occurs inside the CFCD, and then that extra thick part is too fat to slip through the carbide sizing ring when you withdraw the case. Thus, the ring sizes it down, making the rub mark you see as that ring.

The bottom line is the ring is caused when using the Lee CFCD, and the bullets are seated deeper than the case designer intended. Stop doing that, and the ring will no longer be made.

Does this weaken the brass? Yes, a bit. Usually, it is not critical as most of the taper is not in the unsupported part of a chamber, but the case is a little weaker at the bullet base, and I would avoid doing it since the cure is so simple. Again, just stop seating too deeply.