Case mouth ring separation

[09cjones]

Longtime lurker, learned so much figured it was time to join. I have an eerily similar problem with berry’s plated bullets in the Ruger American ranch. Doesn’t happen in Odin works or Q barrels. I narrowed it down to the plated bullets but couldn’t figure out exactly why. Obviously plating and carbon mixed but I didn’t know if it was the allegedly excess headspace of the RAR and low pressure loads not getting a good seal, allowing back pressure to deposit the ring there, or plating shearing off and being forced backwards, etc. Pinched bullets is something I never even considered. Thanks for the knowledge bomb, Dellet. Something else to think about.

[AccelR8]

Hi all. This is not a really a current thread I know but I have relevant experience here.

This is a barrel I made from a 1:8 Green Mountain blank and chambered with a reamer rented from 4D.

After firing many rounds over many months, I experienced the problem the original poster describes. The bolt would not close on a round. The round extracted easily. I looked into the chamber and bore and saw a ring of what turned out to be copper I'm (nearly) certain. It was not lodged but was loose in the chamber and turned sideways. I pushed it out with a cleaning rod and then rounds would chamber fine.

Some months later, it happened again. Bolt wouldn't close. Round extracted fine and looked fine. Tried other rounds, no-go on all of them. Inspection revealed a ring of material just like in the picture the OP posted in the thread.

I was able to remove it with a tight fitting bore brush pushed in from the muzzle.

At this time I began shooting a some soft point 150 grain Hornadys. Very quickly the problem occurred again but this time the ring was lead! I then found out that when a round was chambered but then extracted unfired, it would have a very visible spot where lead was shaved off the point.

I did two things. First, I stopped with the soft points, and second...well I really can't recommend anyone doing what I did. I'll just say it involved a brass lapping rod I custom-made for my chamber with a specifically designed angle and some lapping compound...

This seems to have at least reduced the occurrence of the problem with jacketed bullets. I haven't really put enough rounds through it since to say for sure but I'm seeing no copper build up at all so far.

Based on all of this I feel it's safe to conclude that the cause is material scraped off the bullet during chambering by an edge inside the chamber and this material building up over time and I guess consolidating due to impact, heat, and pressure.

edit to add; when it first happened I assumed it was copper scraped off the bullet during reloading as does occasionally happen with sharp case mouth. But I made sure during loading after the problem occurred that I chamfered all my case mouths and visually inspected each round for shaved copper as they came off the press.

[Kamsmoogs]

Not sure if this is common knowledge or if I came up with a handy trick. In lieu of a 30 cal case mouth bell die, which is needed to load lead bullets, a .357 sizing die can be used. The expander ball, adjusted accordingly, puts a nice consistent bell on 300 blk brass.

[TRshootem]

For case mouth belling for seating lead or coated bullets, I have been using the belling die from a Hornady .357 mag die set. I know many use the 'M' die, but this was handy and has worked just fine. Adjusted to bell the case just enough to seat without doing harm to the chosen bullet.