Thanks for all the info guys...

The rifle is homebuilt. It's an 18" barrel with rifle length gas system, gas block is non-adjustable.

The brass was once fired. Top ones are CBC/Magtech and had the 168s, the bottom Starline brass had the 155s. Not sure how you can tell the headstamp looks flattened?

I wish I had been paying better attention to how the brass was slinging out but I think it was heading more towards the front of the rifle.

Both rounds were using H4895. It's just my stupidity in gauging the load and I really didn't take the barrel length into proper consideration. Guess it's time to pull the rounds and back off the juice! I understand the concept of the brass getting pushed into cracks and crevices but didn't get why it burred. That link helped to explain it....there is a lot going on when that hell is released. I might look into an adjustable block so I can dial it in. I love how soft an AR-10 shoots compared to a bolt gun.