Thread: Case separation, rough chamber, brittle cases?

I had initial thoughts of brittle brass due to the case separation. But after going back through the spent cases, I then thought I may have a rough chamber.

Now, I'm unsure...

We were sending a few 223 rounds downstream on the weekend. Using Belmont 62gr FMJ (Hornady cases) and some PMC 55gr soft points
Marlin 223 and a Bergara 223 single shot.
The Marlin gave us a few misfires with the FMJ, 6 or so out of 80 odd rounds, no issues at all with the PMC. FMJ rounds fired later when run through the Bergara. No markings on cases.

The Bergara was originally a 222, rechambered at some point to 223.
It fired everything we fed it, Belmont and PMC. Thirty or so rounds in, I opened it up to reload and lifted out 1/3 of a case. Uh oh.. I put the rifle aside and spend a few hours with the kids on the .22s.
That evening we extracted the rest of the case with a cleaning rod, it came out freely, no resistance at all. What a relief.
I checked the chamber with a torch, nothing out of the ordinary was obvious. (It was dark too though).
So the next day we put a few more rounds through the rifle. Twenty rounds in and I saw another partial separation when extracting a spent case.
Swapped onto the PMC rounds and 6 rounds set free no issues at all. (Looking closer tonight two PMC cases have a fine ring mark showing)
Cleaning the rifle after the weekend and giving the chamber a good scrub, the machining marks were obvious but there but there is no lip or indent where the cases have been marked and separated. (I think I'll get the chamber polished though)


Looking back through the spent cases tonight and there is an obvious line on a lot of the cases. And a third cracked case I didn't see while shooting.
I am not a reloader and I am an average armchair internet researcher so I am uncertain about this.
In hindsight I should have examined the chamber more closely before cleaning. But I was thinking more of a fault with the cases at that point. But all the cases are marked in the same place so now the chamber appears to be the culprit.
I had previously only put a few sighting rounds through the Bergara myself. So this issue hasn't been apparent.