Case mouth ring separation

[Okiedelta]

Yesterday I was testing some 300 BO load variations/ powder amounts on a 10.5 “ pistol length AR and logging MV. Barrel is new SpikesTactical with about 60 rounds of commercial subsonic Hornady rounds through it.

After approx 25 rounds yesterday the final round jammed on loading, would not go into battery and locked up the BCG. Took a while on the workbench to finally get bolt free and remove the unfired cartridge. I assumed it was unfired and I took all precautions.

On inspection, there is a very small ring of brass jammed in the chamber that prevents the next round from seating and prevents the whole thing from going into battery.

I have searched without luck to find other examples of this happening. The rounds were all reloads, but at the bottom of the ladder. H110 at 7.3 to 8.4 and N110 7.5 to 8.6.
MV were all less than 1200 fps, and most in the 950’s to 1100.
All rounds were 208 g Hornady HPBT. Cases were meticulously measured and evaluated for COAL, headspace, and even weight ( curious as to complete cartridge weight variations across reloading sessions, another day). All had been full length resized. None were crimped. Very slight champfer/bevel by hand before bullets were seated.

I have experienced this once before on a new Bartlein barrel in a custom 308 single shot bolt rifle shooting factory match ammo.

Ring any bells?

[dellet]

First thought would be that it is not brass from the case, but possibly copper from the bullets being shaved off from a sharp edge in the chamber. Not uncommon.

If it is brass from the cases, and they are shorter than 1.368" I would question the quality of the chamber and maybe do a cast of it to measure.

[Okiedelta]

I am going to try and extract the item tonight. I haven’t put a borescope to it yet, but I will do that tonight.

I didn’t think of copper build up because it seemed to happen suddenly, and with the barrel off, I can’t get a cartridge to get closer than about 1/4 inch to fully seated.

[Okiedelta]

Cases are all 1.358- 1.361 at most.

[dellet]

Were any of the brass shorter or obviously missing something?

[Okiedelta]

Cases are all 1.358- 1.361 at most.

I checked the brass and there were a couple that were shorter, but not by more than 3-4 thousandth. Nothing that looked torn or uneven.

[Okiedelta]

I'm just now figuring out how Imgur works, so sorry for the size!
Here is my borescope pic....
Perfect brass circle.

I'm heading downstairs now to try and pick the thing out.

[plant.one]

please post pics of it once you get it out. that might help us more


i almost wonder if you had some burr's on the brass from trimming that lodged a few up in there on you.

[Okiedelta]

I spent an hour trying to dislodge the thing, but no joy. The muzzle end is flush with the barrel wall (of course) so the only purchase is from the chamber end. I have soaked in M-pro 7 and will try again today.

My real issue is understanding why this happened. I haven’t found any similar example in a ‘net search, and it happened once before to me on a 308 single shot bolt custom rifle using commercial rounds.

[Okiedelta]

Now I'm a little concerned.
I thought perhaps that if I could push a 30 cal bullet in from the muzzle end force it through the jammed brass part, it would engage the brass enough that I could dislodge it. I figured the push would not be easy, but I didn't expect the resistance I got.

Maybe this is normal because I have never pushed a bullet through a barrel, but when I started pushing it with a wooden dowel, the bullet almost wouldn't budge. After some significant tapping on the dowel with a small ball peen hammer, I got the bullet to move about a quarter of an inch. I tapped it back out from the chamber end , and when I looked at the land/groove marks on the bullet, they were deeply gouged into the bullet, far more than I expected. I know the lands start off much shallower at the chamber end, and so maybe I should not have given up so quickly.

So I measured the ID of the barrel at the muzzle, I assume on the lands since the calipers were straight, and the calipers showed .297, which I could 'stretch' to 0.302 if I pushed on the caliper.
This barrel is stamped AAC 300.
Is this a mis-marked barrel, or did I give tip too soon?.