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

[markm]

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

That is just horrible. Granted, military ball ammo is terribly inaccurate, but DAMN!!

[ViniVidivici]

Hearing that about spherical powder just makes me.....sad.

[1168]

When velocity or precision falls off to the point I notice. I don’t do a lot of super-precise shooting, but I also don’t have a berm-blasting gun, so my barrels last a moderate round count. I don’t let them go until they keyhole, but I’m also not chasing 1 MOA. Hitting E-types and F-types at 500-600 is good enough for me. Checking zero at 200 or 300 before doing that will generally show how easy or hard 500 will be.

I own a bore cam, but I don’t use it for determining when it is time… I’m not experienced enough in its use. I just think its cool to look at.

Between using a PCC for close-range practice and shooting less lately in general, barrels seem to last longer than they used to.

Hearing that about spherical powder just makes me.....sad.

Anecdotally, some powders seem to erode blast baffles faster, too.

[markm]

Hearing that about spherical powder just makes me.....sad.

Yep. We run almost NO ball powder. I'd say none, but every so often we'll fire a box of factory stuff.

What I use to check barrel wear is that Bullet jump gizmo from Hornady. I had an old bushmaster 14.5 barrel that I rotated out at around 25-30k, and it really didn't have that bad of throat erosion. These days, we shoot too many different guns to wear out a barrel.

[alx01]

Aberdeen Proving Ground has three phase criteria that fail barrels.
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.

I read a paper showing that an old powder (expired surplus mil ammo 15+ years old) depending on the manufacturer will might cause both velocity decrease and a pressure spike. I don't recall the exact details or methodology they used, but it was relative to pressure curves vs newer ammo prior to expiration date.

That article also noted a significant increase in barrel wear when using a surplus ammo past the expiration date.

The M16 spec last I read only required a 6000 round life and of course they are tested with ball propellant in issue ammo.

Not saying you're wrong, but it's hard for me to believe that such mild firing schedule would wear out chrome lined Mil-B-11595E barrels that fast. This is considering the fact that AK-47 barrels in 7.62 can last well over 15k rounds, and those barrels use something equivalent of 4130 steel.

Do you think it might to do something with a higher pressure of 5.56 or a faster twist rate? Do you know if 1/7 vs 1/9 or 1/12 barrel life has been compared?

Knowing the factors around barrel wear, why haven't we updated the powders? How old is the powder formula in M855 and M855A1? I have zero knowledge powders and relevant chemistry. Maybe somebody with area expertise can chime in. I would be interested in learning more.

[mRad]

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.

As barrels wear (usually in the throat), the bullet is making larger and larger jumps. The erosion accelerates after the throat starts to wear. The lands begin to wear down cutting much less deep into the bullet and the seal isn’t what it once was. Eventually, the bullets will no longer stabilize and begin to keyhole. This is a LATE sign and your barrel was already toast.

It would take a terribly huge muzzle incursion to cause a key hole. In fact, you can google the barrel length/velocity test and see where a dude doesn’t even crown the barrel after shortening it with a chop saw. Those bullets don’t keyhole and accuracy isn’t terrible.

The most common cause of keyhole is inadequate twist. Either too slow to stabilize or too much twist at too high a velocity causing jacket deformation. I’ve seen that with shooting light varmint bullets at 4300 fps through a 1:8” 6mm barrel.

At least that is my experience with barrels.


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[markm]

or too much twist at too high a velocity causing jacket deformation.

That reminds me. I have this Sabre Defense 14.5 AR barrel that spins apart 55 gr Hornady soft point bullets. I never did fully figure that one out. It'll shoot everything else normally, but those bullets fall apart.

[Humpy70]

Now that we know more about muzzle erosion from Bruce Woodford I would tend to think there needs to be a study to determine muzzle wear. I know target shooters with bolt guns that have access to lathes and they touch up crowns occasionally.

[lysander]

Not saying you're wrong, but it's hard for me to believe that such mild firing schedule would wear out chrome lined Mil-B-11595E barrels that fast. This is considering the fact that AK-47 barrels in 7.62 can last well over 15k rounds, and those barrels use something equivalent of 4130 steel.

Do you think it might to do something with a higher pressure of 5.56 or a faster twist rate? Do you know if 1/7 vs 1/9 or 1/12 barrel life has been compared?

Knowing the factors around barrel wear, why haven't we updated the powders? How old is the powder formula in M855 and M855A1? I have zero knowledge powders and relevant chemistry. Maybe somebody with area expertise can chime in. I would be interested in learning more.

Mild?

One magazine at one round per second.
One magazine full automatic.
One magazine at one round per second.
One magazine full automatic.
Ten Minutes.
Repeat 120 round cycle.
Forced air until barrel is cool to the touch
Repeat 240 round cycle.
Continue until you get 6000 rounds

One magazine at 1 round per second get the barrel to over 800 degrees at the hottest point, and one 30 round magazine in full auto right after that will get the barrel over 1200 degrees. That's a pretty rough firing schedule.

You can find the standard test procedure in TOP 3-2-45 - Small Arms Hand and Shoulder Weapons and Machine Guns.

And, the reason the Army is so in love with ball propellants is because it shows the least throat erosion of all the typical propellants, that is also why it is so dirty. 1) the calcium carbonate, a by product of the manufacture process happens to be a good erosion inhibitor, 2) all that solid residue holds the heat off the barrel walls until it cools slightly and condenses out, and 3) ball propellant is heavily deterred and has a low flame temperature.

[DG23]

I read a paper showing that an old powder (expired surplus mil ammo 15+ years old) depending on the manufacturer will might cause both velocity decrease and a pressure spike. I don't recall the exact details or methodology they used, but it was relative to pressure curves vs newer ammo prior to expiration date.

I have been loading for a long time and have never seen or heard of any powder (or ammo) with an 'expiration date'.

No idea where you read that at. Would like to read about it if you have a link to learn what powder (or ammo) exactly they were talking about.