300 WM Brass with circle on brass below shoulder- cause?

[DIBBS]

While inspecting and sizing 2x fired Black Hills Match 300 WM Brass tonight, I discovered one case in the lot of brass to be sized, that had what appears to be a perfect circle just below the shoulder.

It was shot in a Bighorn SR3, unknown weather conditions since I didn't see it till now. Would a speck of water cause this, or is it more likely a manufacturing defect that wasn't discovered till now. You can feel it with your fingernail. Thoughts?

I only found one case in the lot of ~75 that I was processing that had this. I'll look at the remainder of loaded cases at the range tomorrow to see if any of them are similar.

 

[WB300]

That looks like the marks left from brass used in a pressure test barrel.

Are they Black Hills Remanufactured rounds?

 

[DHDeal]

WB300 is correct. I bought some Lapua 30-06 years back that was factory ammo used for pressure testing (not proof loads). Still have it and use it.

 

[DIBBS]

I am not sure where I bought the brass, I bought it as once fired and have had it for ~ 15 years before putting it in service. I posted this on accurate shooter as well, and the consensus was that it was a pressure test barrel piston mark as well. Thanks.

Ways to Measure Pressure | The Ballistic Assistant

www.theballisticassistant.com