< 1/2 MOA 6.5 Grendel Barrel?

[lazyengineer]

As a "what-if" to all you engineers out there...
I think the gas velocity until the bullet exits is roughly equal to bullet velocity, during acceleration which would put it all at up to about 2500-3000 ft/sec, and all roughly in the same ballpark.
Until bullet exit, then due to venting of the remaining pressure it escapes at 2-3x initial bullet MV, for that brief time. Wouldn't most of the erosion therefore happen after bullet exit, during that high-pressure vent? If so then gas volume/temperature and pressure at time of exit would relate to erosion. For a 243 compared to smaller diameter/case volume/barrel volumes such erosion would be high: high volume through a narrow pipe... grendels, with less case volume and typically shorter barrels as well as lower final exit gas pressure, would tend to make it low, or lower. A theory anyway.
As to temperatures, I would guess that particle velocity has more to do with erosion that particle/gas temperature. Temperature would mostly affect pressure... thus velocity. But velocity would rule.

This is exactly what I think. In industry, I learned the most erosive fluid on a pipe is actually gas, more than a liquid. And there is a trend in AR pistols I've seen hinted that shorter barrels erode out faster than longer barrels, which at first seems counter intuitive, until you factor in the fact that a short barrel means a larger mass ejection of very-high velocity gasses (and erosive still unburned powder) ejecting to atmosphere once the bullet leaves. It's one of the reasons I prefer running a slightly fast powder, vs a slightly slow powder now (when I have to choose).

And yes, I think you hit on barrel life factors as well, with diameter. Which is why 6.5 barrels outlast the same round necked down to 6mm.