Again, thanks y'all for the contributions, it's good to have stuff to try. HCM, you're spot on that current .300 BLK prices have me wincing a bit at 500 rounds to function test. I am a bit mystified at the rest, birds and warmarks are totally new terms to me and I am feeling very out of my depth on rifle building. Unless you got autocorrected and it was burrs and wear marks. In which case no, the bolt and upper both looked nice and normal to me, but I'm certainly going to have a closer look now.
Let me ask...this is a Toolcraft C158 Nickel Boron BCG. Given that NIB is a thicker coating, and I also have a brand new spare Toolcraft C158 IonBond BCG...might it be worth it to just swap the Nib out for the Ionbond? If it's extra tight, maybe the minutely smaller coating would fix the issue?
If that's a dumb idea sorry, I am just spitballing.