From time to time this comes up. I've wrote about it a lot.
"Barrel life is a direct reflection of rate of fire."
Well...it could be, but it is not a direct reflection of rate of fire, unless you are doing abuse trials.
What barrel wear "is", is a complex pile of data incorporating several factors. Rate of fire could be one of those, but a subsonic 300blk is gonna last a really long time, compared to a 308 irrespective of ROF.
It might surprise you to learn that no barrel lasts more than a few seconds.
Think about that and let it sink in.
At 3300fps a bullet leaves the barrel in "roughly" 1 millisecond. Barrel length plays a role but since I am not a rocket scientist, and we only need rough numbers to illustrate this subject.
Even if you do all the complicated math "barrel life" is relative. Rare is the occasion a barrel goes from 1moa to 5 without a rather gradual sloped graph. It's not gonna be a tack driver today and a dog tomorrow, speaking loudly from Mt Olympus; "You have exceeded your round count".
You might shoot out the barrel on your 9mm, you'd be a very prolific shooter, and it has been done I guess. I've heard guys say they did. You might shoot the barrel out of a 308, it'll take some doing.
The real limiting factor in what is considered shot out is acceptable accuracy. Only the individual can answer that.
Bore diameter x powder column ratio, is a big factor, but you also have to consider velocity in that equation. The higher velocity, the higher the heat at the throat. Flame cutting at the throat is THE factor that wears the barrel. Unless you are talking about a 22lr and that is a whole other bag of ugly snakes. Yes you CAN shoot a 22lr barrel out, I've seen what it looks like through a good friend's borescope.
Not saying don't clean your rifle, but improper cleaning has ruined more barrels than you can imagine.
Velocity is the killer usually, because of the flame temps required to achieve speed. Yes an already overheated barrel will fire crack at a much accelerated rate. Wear becomes exponential at and past about 2800fps it would seem.
My actual dope numbers on my 308DPMS indicate 2820fps with 168gr SMK. It is exceptional for a gasser, an outlier if you will.
6.5 CM in a gasser with 123 class bullets might attain 2900+ safely. Yeah I know what the book says, but the book says a lot of things, and those loads weren't tested with your rifle.
I feel, and so do many others, that the Creedmoor is a superior round to the 308.
The juice is worth the squeeze, as they say. I don't need one because I have a 308 that happened to be a bit fast. I'd have one if my 308 wasn't so fast.
The "need for speed is over rated. The Creedmoor isn't going to negate your need to dope the wind, you are still gonna have to know how much to hold off. I can tell you the 308 with 168 class bullets will tire you out in a match, the Creedmoor...not so much. It does shoot softer.
Buy what you want. Buy what is accurate. Buy what you load well. Buy what you shoot well. The Creedmoor is fickle to load for in a gasser, meaning not near as idiot proof as the 308, not terribly difficult but not dead easy. In a bolt it's pretty easy.
Barrels are an expendable asset, they will need replacing. If you are choosing a caliber on barrel life you are backing up. It should be pretty low on your list of cons. Accuracy is king.
Barrel life between the CM and the 308 is negligable.
