Gunsmithing Possible to not notice chamber issue until multiple reloads?

[Sticks]

I have a MPA 6.5 PRC barrel that I noticed an external ring just before the shoulder about 200 rounds ago (800 or so on the barrel).

I have been running the same 400 rounds of Hornady Brass in rotation. Clean, Shoulder bump and bushing the neck. No other brass work like neck turning or annealing.

Loads are 54.14 gr RE26, 147 ELD with .002 Neck tension. Zero pressure signs or sticky bolt, though after the last cleaning it took a smack on the bolt handle to extract the first few rounds.

I looked inside the chamber with a bore scope and it looks like reamer gouge. I have never used anything resembling a power tool on the chamber, always use a bore guide and Dewy rod with Brass jags and Brass brush. Chamber/neck cleaned with brass pistol brush with push/twist pull/twist motions.

Is it possible that the neck/shoulder area is getting soft enough, or lack of elasticity that it is fireforming into the gouge leaving the ring? I don't have any new brass to check to see if it shows there.

 

[Thud]

Need picture

 

[Mordamer]

Does it shoot good?

 

[Ksracer]

Somebody on FB had the same problem a few weeks ago. A raised ring started to show up on his brass after the second or third firing that wasn't there the first time. He found a groove in his chamber with a bore scope. I believe he said he started to have extraction problems also.

 

[iceng]

Pics are worth more than words. If it shoots good and does not give extraction issues, keep running it, but closely monitor it.

 

[GH41]

I think you answered your own question... The flaw in the chamber was always there but the brass lost the ability to spring back after the first firing.