Case mouth bulge or belling when sizing .260?

[Tim K]

Rem .260
Lapua Brass - 6 cycles
Redding S full length bushing sizer, .293" bushing with the expander ball
Loaded neck diameter = 0.294"

I'm getting a condition where the last 0.050" of the case is bulged or belled about 0.004". To be clear, this is happening at the case mouth. The main diameter of the neck measures 0.293" after sizing, and the very end of the mouth measures 0.297" The bulge starts about 0.050" from the mouth. I don't remember seeing this when the brass was new, but I may not have been looking. It got so bad one loading that the rounds wouldn't chamber. I didn't think to measure those. I'm also getting some shaving of the bullet when seating, even with a light inside chamfer from a standard (not VLD) deburring tool.

My chamber dimension is 0.299" (fired brass measures 0.298"), and there is no lip or bulge present on fired brass. It's clearly a product of the sizing process.

Thinking the brass might be getting hard, I annealed 25 pieces this morning. They showed the same bulge after sizing. I have not seated bullets yet so I don't know if it will still be shaving copper.

Any idea what's going on? Is this just normal and I've never noticed?

[Tim K]

Update.

The annealing fixed the shaving of copper when seating bullets. I hate annealing, but I guess it needs to be done. The lever effort was much lighter seating bullets into the annealed cases. The bulge is still there though.

[Jamnanc]

Are you crimping? Or is this just after resize?

[Tim K]

No crimp.

Here's a pic. The larger diameter begins just 0.050" back from the mouth and goes to the mouth. It's more a burr than anything.

[TFOGGER]

Is it possible you're getting brass flow forward from the case shoulder, making the case neck thicker than normal?

[ColoWyo]

I would think flow as well. But I'm no expert. I just went and measured 5 Lapua .260 cases (re-sized) and they were all .290 and .290 where you marked yours in the pics.

[Tim K]

The case neck thickness measures 0.015" except for the very mouth. That's the same thickness as when it was new. I don't think it's flow, but hell, I don't have a clue.

[clocker]

Does the fired brass have the same neck measurements or is it more uniform? I'm guessing that it has something to due with the Redding die. Have you taken it apart to inspect that the bushing is installed correctly and that the expander ball has not picked up any brass?

[Tim K]

I suspect the die, too. I disassemble, clean, and inspect it after every use. Nothing is wrong that I can detect.

[Hoser]

Take a measurement after you seat a bullet.

I bet it isnt a big deal at all.