Stainless Steel Barrel Life, 1 MOA @ 400 yards

[TheGunGeek]

I have a Knights SR-15 LPR with the stainless barrel as my precision AR. I've researched extensively, and the general consensus is the barrel life should last to ~5,000 rounds @ 600 yards.

My question is after this point is reached, what the estimated life-span would be to maintain 1 MOA out to 400 yards. I'll be shooting no more than 10 rounds at a time, with at least a couple minutes between strings.

Essentially, I'm debating on whether to add a 16" chrome lined upper so not to put unnecessary wear on the precision upper, or to downgrade it to 400 yard duty once it reaches this point, keeping the overall "feel" the same (and have another precision upper). I read about one person who had 15k on his, however he was only shooting at 50 yards so it's not relevant.

I'm very new to long distance AR precision, so input from those with more experience is appreciated.

 

[T. O'Heir]

You should add a 16" chrome lined upper because you want to. Even though you'll lose a bunch of velocity.
The distance you shoot at has nothing to do with barrel life. The load you use can though. There is no estimating any of it. Too many variables involved.
Barrel life is about accuracy and that's defined differently by shooters of different disciplines. 400 isn't an NRA High Power or F Class distance. 300 and 500 are though. The 'black' on a standard 300 yard military target is 19", 24" at 500. 17 7/8" on a, F-class 300 yard target. The 'X' ring on a 300 yard target is 2.85". Which is a bit less than 1 MOA. So you can see how varied the whole thing is.
Barrel life really isn't something you should be worrying about either.

 

[HiBC]

There is a lot of hypothetical to your questions,and a limit to how much I can help you.
Yes,of course a chrome lined barrel in a spare upper will be a good investment if you want to extend the life of the original barrel.
FWIW I built a 5.56 with an 18 in Daniel Defense chrome lined hammer forged S2W profile barrel. Its free floated,1 in 8. I'm not going to offer a "bragging MOA" number,but it stays inside 1.5 MOA at 100 yds with 75 gr Hornady BTHP for 5 shot groups. Chrome lined does have a reputation for being not quite as accurate,but chrome barrels can shoot pretty good. Maybe some are made with more care than others.
I think a lot of barrels that get chrome lined are spewed out to meet low bid contracts,and they would be mediocre chrome lined or not.
I can't say I know through testing or personal experience,it is generally accepted that non-chrome barrels deliver better accuracy,but it may well be that if you begin with a barrelmaker who carefully makes accurate barrels and chrome one you might get a pretty accurate barrel. Just my guess.

I've read that stainless barrels break down in an "alligator skin" or cracked dry lakebed pattern. They can continue to shoot pretty good till you start shedding chunks.

 

[Jim Watson]

Buy another upper? Well, yes, your "good" barrel will last longer if you don't shoot it.
I'd rather use it up and replace it with another of equal quality.

It's service life depends on your expectations. My rifle shooting resource says he got 4600 rounds (.308) shooting High Power with a sling. But F class with a bipod and a target half the size, 2500.

 

[TheGunGeek]

Basically I'm looking at service rifle style competition plus other precision training and events. No bench rest shooting.

My thought process was:
Option (1) when accuracy loss becomes unacceptable at 600 to use it for closer range training and events. Then use the "good" upper, eventually replacing the barrel on most worn, rotate & repeat.

Option (2) use the 16" upper for "closer" range training and events saving wear on stainless steel barrel, and then replace barrels when necessary. The downside to number 2 is the weight is less, so the ergonomic feel will change a bit.

Option (3) would be just don't worry about it and change the barrel when needed.

It appears from the answers like (1) really isn't a good option. It's either go with option (2) or more likely (3). We only know what we know, and I'm learning and collecting data. Thank you all for the input.

 

[hagar]

Distance matters. My NM AR with stainless Douglas barrel went south at about 5500 rounds, was still accurate at 300 yards but could not hit the broadside of a barn at 600. I could see something was going on, as I needed more and more clicks up as time went by. Some of my short range uppers were still accurate at 300 after over 8000 rounds, but I never would have taken them to a full distance match. It's actually throat wear that causes the accuracy to fall off, not barrel wear.

 

[Jim Watson]

Worst case I ever saw was the very nice rifle that shot OK - not great, but OK - at 600 yards but that was its last gasp. It could not keep them on the six foot backer at 1000 an hour later.

My rifle friend had that happen to a M1A, the rapid fire was the last it would do; slowfire the next day was wild.

 

[TheGunGeek]

Distance matters. My NM AR with stainless Douglas barrel went south at about 5500 rounds, was still accurate at 300 yards but could not hit the broadside of a barn at 600. I could see something was going on, as I needed more and more clicks up as time went by. Some of my short range uppers were still accurate at 300 after over 8000 rounds, but I never would have taken them to a full distance match. It's actually throat wear that causes the accuracy to fall off, not barrel wear.

Thank you, that's the data I was looking for. Yes, from what I've read it's the throat wear that results in gas leakage, causing velocity loss and accelerated wear.

I went ahead and ordered a matched 16" carbine upper simply because it will be good to have. Looking forward to competing in 2020.

 

[Bart B.]

The top ranked competitive shooters using AR15 rifles in 223 rebarrel about every 3000 rounds. Ditto for benchresters shooting 22 caliber cartridges the same size as the 223 Remington.

All barrels will eventually shoot a given load's bullets a bit slower and require more sight elevation at longer ranges. Accuracy also degrades and at some point no longer meets some standards. The cause is not gas leak but instead less resistance to bullets entering the chamber throat and bullets increased jump to the throat as it erodes .001" down the barrel every few dozen shots.

 

[TheGunGeek]

The top ranked competitive shooters using AR15 rifles in 223 rebarrel about every 3000 rounds. Ditto for benchresters shooting 22 caliber cartridges the same size as the 223 Remington.

All barrels will eventually shoot a given load's bullets a bit slower and require more sight elevation at longer ranges. Accuracy also degrades and at some point no longer meets some standards. The cause is not gas leak but instead less resistance to bullets entering the chamber throat and bullets increased jump to the throat as it erodes .001" down the barrel every few dozen shots.

That's interesting thank you.

 

[Bart B.]

Military 30 caliber throat erosion gauge heads have a taper of .010" per inch starting at .2990" diameter up to .3090". They go 1/10th inch further into the chamber throat every ~1000 rounds in 7.62 NATO barrels, every ~900 rounds in 30-06 barrels.

 

[Unclenick]

The 5.56 and .308 barrel life is similar. In the late '90s, Precison Shooting published an article by then Sierra ballistics technician Kevin Thomas, who shot out several chrome moly and stainless match grade barrels in .308 firing their standard test load for the 168-grain SMK from a machine rest using a special lot of bullets that were set aside by Sierra for reference work because they turned out to be extra-accurate. The chrome-moly went down at 3,000 rounds and the stainless lasted 3500 rounds. The stainless went to 4,000 rounds when it was cryo-treated, so you could maximize your match barrel life by doing that to it. Thomas reported that he declared a barrel shot out when the first flier appeared.

That matches how I've seen them go down. I've not had one go suddenly, the way Jim Watson described, though that is perfectly possible depending on exactly how the throat broke down and how much muzzle funneling there is. The mode that I've seen is that all is well and then suddenly you get an uncalled flier. Over a relatively short time (100-200 rounds), those fliers become more and more frequent. When I shot out my first M1A barrel, I was shooting well enough in the local reduced range matches to regularly clean the 100-yard reduced prone slow fire targets. So, I'm in the middle of what I expect to become another 20 tens and Xs one afternoon when an uncalled 9 at about 10:30 appears. By the time another 50 rounds went through it I was getting 2 in 20, all 9s in that upper left quadrant of the target. After another 50, it was 4 in 20. At that point I finally wised up to what was happening and stopped blaming myself and got another barrel.

If I'd kept that barrel, fliers would eventually fly even wider and the spread would have been greater. My main point is, the first flier was wide enough that it had immediately become impossible for the gun to clean slow fire targets at any distance. I suppose it would have cleaned the standing slow and the rapid fire targets because the number of moa in their 10-rings is bigger, but I'd have to be shooting better than before to keep it there. The barrel was just gone as far as being an over-the-course barrel. There was no change in acceptable range. It was bad for all of them all at once. It is possible that by 600 yards, given that moa spread out over distance, it might have given me 8's instead of nines.

 

[Bart B.]

Some years ago, I developed a formula to calculate barrel life based on data from Sierra Bullets and top ranked competitive shooters experiences. It's based on match grade barrels testing 1/4 MOA average for 10 shot groups until average was 3/8 MOA. When powder charge weights were at bore capacity, barrel life was about 3000 rounds. Bore capacity is 1 grain of powder for each square millimeter of the bore cross section area.

Charge weights 40% more than bore capacity got 1500 round barrel life. Charges 100% more than bore capacity produced 750 round barrel lives. It's based on the inverse square root laws

Double the barrel lives for hunting rifles shooting groups 2 to 3 times as large. Triple or quadruple them for military service rifles shooting groups 4 to 5 times bigger.

Barrel life can vary 10% across powder heat indices, hotter ones reduce the barrel lives.

 

[Unclenick]

There has to be some underlying assumption about the pressures and temperatures involved to make that work. If I load Hodgon's maximum IMR4064 load for a 168-grain match bullet in .30-06 (50.8 grains or 1.058% bore capacity) and put the same load in a .300 WM where the peak pressure drops 42% and the velocity drops 11%, I would not expect the 300 WM barrel to wear out just as fast as the 30-06. I would not expect that because the surface of the throat is being subjected to a lower temperature and pressure impulse, therefore transferring less heat into its surface and creating less of the surface-to-substrate thermal stress that ultimately causes the crocodile skin cracking pattern that damges a throat.

 

[Bart B.]

Nick, the powder heat index plays a role too. Hotter burning powders cause faster wear rates than cooler ones. A guy on Accurate Shooter forum modified my formula to make a correction:

https://www.accurateshooter.com/technical-articles/excel-formula-predicts-useful-barrel-life/

The above link mentions some benchrest barrels are considered worn out when they no longer shoot groups in the ones; under 2/10ths inch/MOA at 100 yards. Yet several-group aggregate records include some groups larger than 2/10ths inch. His standard could mean no groups in the ones are no longer shot regardless of the largest one's size.

Here's a different approach:

https://www.accurateshooter.com/technical-articles/overbore-cartridges-defined-by-formula/

 

[Nathan]

To me, the question is do I buy this lesser accuracy practice upper or....?

I would do the or....that is, I would put my bits in a piggy bank. Then at 3000 rounds, I should have enough saved up for a new barrel and bolt.....order those up and be ready to pull and replace my original barrel, when the time is right. More shooting is usually a better choice than more guns.