Just saw one of these last week. I think it was HSM ammo, except the owner slipped a .300 blackout case in there!
A number of years ago, a shooter did similar with a 300 whisper in an AR. The barrel maker sent in photo's of the projectile which he was able to hydraulically remove. Said the barrel was still good as new once cleared and the shooter had created the first 168gr, .224 bullet. Don't recall what happened to the rest of the gun
