Jacket Separation on .300 BLK 220 gr Subs
TL;DR - The pic shows a single shot at 10 yds on a clean target, that's jacket separation and tumbling, right? Is this a rifle or an ammo issue, what should I check first? Should I be worried about barrel damage?
I have a brand new Sig MCX Spear LT 9" (1:5 twist), bought some low cost .300 BLK subsonic 220 gr FMJ that was highly recommended in this sub and tried to zero it for the first time today. About half of the rounds that actually hit the target were consistently accurate with round holes, the other half looked like they tumbled and/or fragmented and most of those were off the paper completely. It was random when it happened, I had good and bad rounds throughout the session.
The rifle was cleaned prior to shooting it for the first time today and the barrel looked shiny and clear with no defects that I could see. I did not shoot with a suppressor, I wanted to see how the ammo performed first and I'm glad I waited.
I only had the low cost ammo with me today, so I didn't try another brand or grain for comparison. I'll leave the ammo manufacturer's name out of it for now until I figure out if this is a rifle or ammo issue. The ammo website didn't mention anything about twist rate limitations.
Looking for some advice on what to do next. I put about 75 rounds though the barrel today with this ammo. Since a lot of the bad rounds were off the paper completely, it took me a while to realize what was going on. What damage should I look for in the barrel?
Edit: Didn't realize the brand was that important, it was HSL.