Barrel life, how do you determine your barrel has had it?

[Humpy70]

Just wondering how you all determine when your barrel is shot out.

[MistWolf]

When it can no longer produce the precision required by the job. Or the bullets start keyholing. Whichever comes first.

[alx01]

Just wondering how you all determine when your barrel is shot out.

Significant degradation in barrel accuracy from your accepted baseline. Some people don't replace barrels until they start to keyhole at 50 meters. Which, in my opinion is both wrong and dangerous.

For me anything beyond 5-6MOA with cheap/range ammo or over 3MOA with match ammo is unacceptable even for a range gun and barrel gets thrown out. I'm not an accuracy snob by any means, I just don't like to guess why a rifle won't group.

Unless you have a large and high volume sample size of the same barrel type (like a military might have) it's almost pointless, in my opinion, to do gauging for a regular person.

Accuracy degradation starts at a longer range - your heavily used barrel might shoot 8MOA at 200-400m, but might still shoot fine 3-4MOA at 100 for a few thousands more rounds. That's why you often see discrepancies when some people say 5k rounds while others say 30k rounds.

If I recall correctly, most military in the world have 12-20k rounds of barrel life requirement for a rifle regardless of a caliber or a rifle type. Sure, some examples can live up to 50-60k or even more rounds, but those would be outliers.

[opngrnd]

OP-you may find this thread interesting:
https://www.m4carbine.net/showthread...s-)&highlight=

[17K]

I had around 17K pretty fast tempo rounds through my last barrel (Colt 6920) and it started throwing flyers when we’d confirm zero at 100. No keyholing or anything crazy, but 2 or 3 uncalled flyers in a 10 round group so I swapped it out as it’s just a few minutes at the bench and I have several spares in stock.

[mRad]

First thing I will notice is random flyers. Second, I’ll notice that it slows down; by more drop or by chronograph. Then I will look at the bore with a bore scope. I’ve only worn out a few AR barrels but several bolt-gun barrels.


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[ViniVidivici]

When it can no longer produce the precision required by the job. Or the bullets start keyholing. Whichever comes first.

This is what I came here to say.

I've seen a worn barrel that was still grouping 3 MOA at 100yd, but was keyholing here and there. Done.

[SteyrAUG]

This is what I came here to say.

I've seen a worn barrel that was still grouping 3 MOA at 100yd, but was keyholing here and there. Done.

Wouldn't keyholing be more indicative of a damaged crown vs. a worn barrel? I've seen guys with steel cleaning rods inserted from the barrel end F over their barrel enough that it started just randomly printing anywhere on the target. Of course they blamed their "POS AR rifle."

I've got some WWI firearms that have just a hint of rifling left, they put up big groups but never seen them keyhole a round.

[Humpy70]

Aberdeen Proving Ground has three phase criteria that fail barrels.
Loss of dispersion Exceeds 7.2" extreme at any time at 100 yards.
Loss of velocity (200 FPS loss of velocity) Per my contacts in the ammo test section they could not remember a barrel dropping off velocity causing such. All the others are rejected by yaw or dispersion.

15 degree Yaw of bullets at 25 yards. This is evidenced by the bullet holes in card stock become elongated.
Weapons systems are adopted and specifications are written. For the AR rifles acceptance dispersion must put 10 shots under 4.5" at 100 yards with select ammo. All 5.56/M855 ammo is not equal. Prior to the SCAMP lines weapons were tested initially and every 1200 rounds with ACCEPTANCE AMMO . 5.56 ammo IIRC had an acceptance requirement of 1.5" Radius at 200 meters. All the rest has to shoot in 2.2" mean radius or less. The 1.5" ammo is not issued to troops but reserved for new weapon acceptance and Aberdeen PG use. The run of the mill ammo is used for endurance testing.


Most M16 family weapons came in shooting between 3.5" to 4" for 10 shots at 100 yards.



When a Technical Feasibility Test is undertaken to qualify a new weapon the acceptance dispersion is fired on ten rifles and after pre test records recorded. Three of the ten are selected for endurance firing and consist of the best shooting, the middle and the worst shooting rifle and subjected to 1200 round endurance in 120 rd segments. Two 30 shot mags, 3 shot burst and two 30 shot mags fired semi auto.


At the 1200 round point the three endurance rifles are subject 10 shot dispersion, chronographing and yaw testing with the 1.5" acceptance ammo. Between the 120 round segments the rifles are placed on a rack and high pressure air is injected in the muzzles and the barrels are cooled quickly before the next phase.
A good gun crew consisting of three personnel can run 10,000 rounds per day. In one instance I remember we ran 10,000 rounds a day for 14 straight days.
Depending on who loads the ammo I have seen AR barrels right at rejection (which is 7.2" at 100 yards) at the 4800 round point. I have fired other ammo made by FN and the barrels were right at rejection at 12,000 rounds. (Choice of propellant can shorten barrel life or increase barrel life. Basically ball propellants eat barrels for breakfast where stick propellant is much easier on barrels.



The M16 spec last I read only required a 6000 round life and of course they are tested with ball propellant in issue ammo.
I am only aware of one AR barrel that will hold up far longer than standard chrome lined barrels and these were made by Superior Barrels ( aka Hard Blue)who ceased business four years ago. To my knowledge the makers told me they had never had a shot out Hard Blue come back for rebarreling. Superior to my knowledge never revealed their treatment publicly. Before their treatment each barrel was subjected to 100 rounds to break the barrel in before the treatment was applied.



I have noticed fliers out of the shot groups at 100 yards when the round count got up to around 4000 and they always threw wild shot out the left. I had a friend who worked for Sierra bullets and he told me their bullet test barrels exhibited the same out the left wild shots before they really let go.

Last I heard most good match shooters replace barrels at 2000 rounds. I saw a segment on TV a few years back where the Army Marksmanship Unit replaced barrels every 700 rounds

[ViniVidivici]

Wouldn't keyholing be more indicative of a damaged crown vs. a worn barrel? I've seen guys with steel cleaning rods inserted from the barrel end F over their barrel enough that it started just randomly printing anywhere on the target. Of course they blamed their "POS AR rifle."

I've got some WWI firearms that have just a hint of rifling left, they put up big groups but never seen them keyhole a round.

It's very possible. I don't know, maybe there's a different coefficient for stabilizing 5.56 vs. other rounds, so to speak.

I would assume, barring any damage to the crown as you suggest, that it would indicate worn rifling and therefore lack of stabilizing.

Nobody put a scope into this particular one I observed, it was just pulled and replaced.