< 1/2 MOA 6.5 Grendel Barrel?

[Lemonaid]

I guess another question is

How do they get 10,000 plus rounds through a 5.56? It has an even smaller bore.

I have a 5.56 that has 8,000 rounds through it, and it still shoots good.

The little 55 grain pill is going 3,000+ FPS

Read about this from Glen D. Zediker's book handloading for competition (page 188), boiled down its the heavy for caliber bullets that cause the most throat erosion due to shorter pressure time curve, "A heavier bullet gets started slower, the pressure behind it is confined to build and peak in a shorter distance."
A 5.56 has less powder behind it pushing a smaller weight bullet than the Grendel or 6ARC so less erosion. I'm not informed about barrel life of a fast twist 5.56 using the heavy bullets but it should be less.