I have found and purchased 250 once fired cases of 6mm ARC. Some I found here, and some from an online supplier. Fifty cases were fired from an individuals gun, and all fifty of those had a very pronounced bulged line around the web of the case, about a 1/4 up from the face of the head. The ring was easily felt when I ran my fingernail across it. I sent a pic of them to Hornady, and they said the brass was toast due to excessive headspace in the rifle.
The other 200 came from factory rifle test firing. All once fired, these are factory Hornady rounds fired for testing the function of rifles before they are sold. Out of the 200, 76 had the same telltale bulged line around the web of the case. Some only had the bulge halfway around the case, others had it all the way around. None of these were as bad as the first fifty cases, but I could still feel the bulged line with my fingernail. I have yet to split one open, but this seems to be quite a few cases that are showing the problem, and it makes me nervous to reload a case that may have a weak point. It's just not worth the risk to me. When I contacted the supplier, he said he doesn't have time to pay someone to sit around and check cases. "Just run them through a small base die and that ring will go away" he said. He seemed to be kinda pissy when I said that they could be a potentially dangerous to reload if they have a weak spot, and that I was just letting him know what I am seeing. He offered to send me replacement brass, but I declined, since I would most likely just get more brass that had this issue.
I have a 6mm ARC, its a CMMG Endeavor gas gun, factory new. I fired 5rounds of Hornady Black 6mm ARC ammo through it for a function test and brass check. All rounds fired, chambered and ejected as they should. There is a discolored halo up the web from the head that ends exactly where the ring began on the bad cases, but no bulging on my brass.
Is anyone else seeing this? Hornady insists its a rifle problem, and I would tend to agree. I also know that a new cartridge comes with teething problems that can be found in rifles, barrels, bolts and cases. I have given up on purchasing once fired brass, and I will only use the brass that I form myself or is factory ammo fired from my rifle. New brass still seems to be non existent at this time, and unless you can find a good deal on ammo, it's almost cheaper to shoot 50 cal.
Maybe I'm just a bad brass magnet for this caliber, but if you have seen anything like this I would like to know the story.
Cheers,
Dave