Thanks to both of you, really appreciate any thoughts! Thanks for the heads up on the primers and, yah, I would buy lapua or petersen for brass...if I was richer. lol! That creates a side question, although premium brass is way more expensive, does it last that much longer when reloading belted (assuming I go all in and do it properly, ie. neck'em, FL as needed only, anneal and perhaps magnum collet for head)? Premium brass certianly worth it in non-belted, but curious as to guys thoughts on that too with belted. Maybe I should just bite the bullet and get the good brass, lol.
That said, it's a new factory Bergara B14 HMR and the ammo was new factory ammo too. Oddly, I also shot out a half box of Hornady ammo and no such partial splits/ring at all. The ring is only about 1/3 of the circumference. Can't say I inspected or noticed the split before firing, didn't look. Bullets were on target (ish, lol) out to 500+ yards (first day out with it), I didn't use a chrono or anything so can't say I noticed anything else different about them. Maybe just a bad batch of Federal?
I will get into the chamber and look for any burrs , could explain it perhaps, but odd it was only on some shots, IMHO. Temperature was about 41 degrees so maybe that was a factor but it shouldn't be at that temp? I paced the shots too so the barrel was not running hot either. Also swabbed the barrel after every shot or two. Now, having said that, perhaps you have helped me solve this one. I shot 40 rounds of Federal, with issues as mentioned, then 10 Hornady and nothing. Could be just a barrel break in issue (which I didn't notice until back home and inspecting for reloading)?