Possibly least educated, and anecdote based opinion: More to address the OP, I was a militia bum for a few years, and we never followed a break in procedure. As a matter of fact, my newly issued rifle when I got to garrison was not only new to me, but actually new. Which was a welcome change from the rifle I was issued during basic, in wainwright AB. No telling how many thousand rounds went through that.
Well, it's first range trip was to shilo, to rid ourselves of our remaining training allowance of ammunition. Any one who has gone on one of those wasteful and wonderful trips to the range knows what a torture test that can be for firearms. Occasionally we even split machine gun barrels, not to mention melted plastic from setting them down on sandbags. I started actually trying to get perfect hits on my targets, until a master bombardier told me we'd be there all night if I shot like that. "Go crazy, flip the switch to fun". Mag after mag in full auto. So as you could see in the darkness, little rays of orange light beneath the hand guards. That rifle was so full of carbon, it looked like it was furry.
And that same rifle got me my marksmanship badge the next two years in a row. And while that was the worst abuse I subjected that rifle to, it was not the only one. I'm sure at 500m it's performance may have been affected, but for most, that's the domain of bolt rifles anyway. Like I said, just one mo-bums experience.
