Case carbon pattern

[chindits]

What does this carbon ring below the shoulder indicate?

I was in a hurry shooting as the sun was going down and the temperature was dropping below zero. It was probably mid group. I was only shooting 2 shot strings, mark target and change position. It was the only case of 12 that had this pattern. This group of 6.5 cm brass has been loaded 5 times with a moderate load of 147eldm/40.5g H4350.

 

[Lawnboi]

Gas leakage.

Clean your chamber and keep shooting. This happens, especially when shooting suppressed.

Smoke on your chamber walls and sticks due to pressure gradient, next case dosnt stick like it’s supposed to.

This is just my observation.

 

[chindits]

Okay thanks

 

[RockAndSage]

Okay thanks

It's very likely exactly what @Lawnboi said, but I'll add one other possibility just in case: ensure you don't have any oil/lube/case lube in the chamber at all or on the casing. In addition to fouling possibilities, lube in a chamber dramatically increases the pressure on the bolt lugs. The forces in the burning powder try to apply equal pressure to both bullet and casing, but it's the nature of brass to stretch and turn into a seal against the chamber walls, soaking up somewhere around half of the pressure by applying it to the chamber walls instead of the bolt face. Lube it, and bolt-face pressure increases substantially.

 

[Lawnboi]

This can also happen when you run too low pressure. I’m guessing from your load your not even close though

 

[chindits]

Good info thank you.

I haven’t been cleaning my rifle much at all. I keep it in the garage and it never gets warm this time of year except in the truck for that 15 minute drive to BLM. I have cleaned the chamber when the bolt feels a little draggy every other month or so. Just a wet patch then a dry patch, no lube after cleaning. Hope’s 9 because I like the smell. Maybe the barrel has been cleaned a couple times in 500 rounds.

I’ll keep shooting like usual through the winter.

 

[chindits]

My cases get cleaned before and after sizing. Just a paper towel with alcohol. I’ll pay more attention to that.

 

[TaperPin]

What does this carbon ring below the shoulder indicate?

I was in a hurry shooting as the sun was going down and the temperature was dropping below zero. It was probably mid group. I was only shooting 2 shot strings, mark target and change position. It was the only case of 12 that had this pattern. This group of 6.5 cm brass has been loaded 5 times with a moderate load of 147eldm/40.5g H4350.
View attachment 802104

Looks like gas leakage to me as well, although I’ve never had it in that area - that’s cool to see something new. The case seals first at the neck normally - new or annealed brass is soft and often seals at the mouth. Each time it’s fired hardens the brass so it seals at higher pressure and might seal where the neck meets shoulder, or on the shoulder. Dirty chamber also effects sealing, usually at the mouth first, then farther back as crud builds up. Thicker brass seals later in the pressure curve.