Any thoughts on expected barrel life for the M15-Sport using medium power loads?

Really no such thing as medium power .223 loads. High power competitors change out barrels every 2000-4000 rounds, depending on their shooting ability and the quality of their barrels. Melonite treated barrels generally last way longer. How long will depend on your accuracy requirements.

It should get you through a couple of boxes of ammo okay... Just don't shoot more than 3 or 4 rounds a minute.

.

__________________
Kirk / Spock 2020

Not too long ago I stumbled on an article testing for barrel life with steel jacketed Russian ammo and USA made copper jacketed ammo. At about the 4000 round mark they started to see keyholing in the target with the rifle running the Russian ammo and at 10,000 rounds the rifle running the USA made ammo still was capable of 2-3 inch 100 yard groups without any keyholing.

After the testing was concluded the barrel were split lengthwise using a wire EDM so that microscopic examination of the barrels could be done. The rifle that was using the steel jacketed Russian ammo had a barrel that did not have any measurable rifling, the barrel using the copper jacketed ammo still had fairly good rifling but the throat area was pretty much done in.

So, your answer depends on what type of ammo you are shooting. If you insist on running Brown Bear with copper plated steel jackets you should probably plan on replacing the barrel somewhere in the 2000-3000 round mark. If you limit your ammo selection to brands featuring copper jacketed bullets you can probably keep shooting with Combat accuracy up to somewhere around 7-10 K rounds.

Yeah, I know that sounds like a rather miserable barrel life considering that most AR's today feature chrome plated barrels. It's a function of the velocity of the bullets. if you over simplify it Classic Physics states that energy is a function of the Velocity Squared and one could expect that wear to the barrel will also increase at a function of the Velocity Squared. Basically a barrel operating at 3000 fps will wear at a rate that is 4 times than of a barrel operating at 1500 fps. Add in the higher surface temperature due to the friction at the higher velocity and you probably have another factor that increases wear in what is probably another geometric function. Boil it all down and if you double the velocity you probably shorten barrel life by a factor or 8 or more.

I was reading an article on Melonite processing at AccurateShooting and read the following: "after processing, barrels deliver 50 to 100 fps LESS velocity with the same load, a reliable indicator of reduced friction. (Likewise, you’ll get less velocity when switching from naked to moly-coated bullets.)"

Can someone explain this to me? Seems backwards or????

Less friction means the bullet did not seal the chamber quite the same as on another barrel. The friction means the bullet 'sticks' in the barrel more, meaning more pressure is realized as the bullet does not move quite as quickly. As more pressure is built, the bullet eventually will achieve more velocity because the energy stored behind the bullet increases by the nanosecond as combustion occurs. Soon, enough pressure is contained to send the bullet that much harder, resulting in higher exit velocity.

Long range rifle mumbo....... not so practical to a 16" carbine barrel.
And, the Sport barrels, and ALL there AR barrels tend to hold up pretty well to 30,000 or more rounds, time and time again. The thing which affects accuracy is the deterioration of the throat of the barrel, where the bullet actually hits the rifling.
I have found the story behind the steel ammo is just that, a story..... and the results were created by optimizing barrel wear thru very particular shooting.
.mil AR's tend to hold out to 30-50K before being retired. And....YES; they still have rifling. They are not worn smooth, like the story. And lest we forget, the xm855 and 193 ARE FMJ rounds. The throats are burned up, and that is why they do not stabilize a bullet well.

Really hot ammo eats the throat fast because the excess combustion lends itself to etching and pitting away the metal at the throat.

Of course, this all depends on what you are looking for in accuracy, and to what distance. If you are looking to hit a pumpkin at 50 yards??? 50,000 rounds. If you are looking to hit that same pumpkin at 600yards????? Your barrel will not deliver that kind of accuracy for 50,000 rounds. With careful shooting, maybe 4,000. Maybe 15,000. It would depend a lot on how the rifle was shot for it's life, how well you adapt to the rifle and how it shifts POI, the optic used, etc. The same shooter with the rifle will see less fall off in performance because they will naturally adapt to the changing shooting dynamic.

Thanks for the explanation.

It should last you a year or so.............


Yes, I'm joking. It all depends on how many rounds you shoot.

__________________
Still carrying my S&W 642

The honest answer is that with good care the barrel will likely last as long as you need it to.

I have a friend who's put 10,000 rounds through his AR and it's still very accurate so it's got many more rounds to go. I'd be happy if mine lasts that long since I have two ARs and split the wear between them.

The longevity of the barrel also is how fast you are shooting those 4000 to 10,000 rounds. You do a mag dump 10 times a trip compared to shooting slow from a bench are two different things.

Outstanding point. It's not like "we're" are in a combat or free fire zone and these are "Combat" MSR's. I NEVER do mag dumps and keep a VERY close eye on the barrel temps. Not that I never get my barrels hot, but if you can't hold the barrel with a light glove on, you are getting the barrel way too hot and doing damage. Getting the chamber too hot can also set the round off from over heating with-out a primer strike and do damage or even distroy the barrel not to mention harming the shooter and any bystanders.

__________________
THIS WE'LL DEFEND ΜΟΛΩΝ ΛΑΒΕ