That load is max with standard primers (Nosler data). Instead of trying to figure out what happened, I'd suggest starting over with load development for the new barrel and pull that old ammo down, save the bullets, and sh*tcan that brass, especially if it was loaded a few times.
Personally, I'd never use max (or over-max) level reloads in a rifle they weren't developed in. Just looking for trouble. Looks like you found it.
