Lifespan & wear of 5.56 AR barrels vs. .308 AR barrels.

[Cane55]

With all things being equal (steel type & coating/treatments etc.) which caliber wears out the barrel sooner between the 5.56 AR15 and the .308 AR10? Does one caliber last for higher round counts than the other? I know the .308 is obviously a bigger bullet but I've also heard that the 5.56 has greater chamber pressures, so does anyone know which barrels wear faster/last longer (all things being equal).

[gaijin]

While I've shot tens of thousands of 5.56 in my ARs, I doubt like hell I'll ever duplicate that through my few .308 ARs.
It would take deeper pockets and dedication than I have.
My gut says the 5.56 will erode a barrel quicker than .308, guess I just feel it's irrelevant in my case.

[SomeOtherGuy]

Major factors in barrel life are:
-material and lining (if any)
-quantity of propellant relative to the bore diameter and bullet mass - the more you have, the more "overbore" a cartridge is and the faster it wears out
-flame temperature of the propellant (modern double-base powders are getting hotter and hotter) (this also goes with pressure)
-bullet surface material (jacket, or the overall material if a solid lead or solid copper bullet)
-shape of bullets used - boat-tail bullets tend to allow more gas blow-by which causes more barrel erosion, especially at the throat

Of these the "overbore" or amount of propellant vs. bullet weight and bore diameter is the only consistent difference between 5.56 NATO and .308 Win. The 5.56 NATO is slightly more overbore, with approx 24-28 grains of powder for a .224 bullet vs. 40-45 grains of powder for a .308 bullet; the .308 has slightly less than twice the bore area of the .224.

Therefore, with identical barrel construction, propellants and bullet construction, I would expect the .308 to have somewhat longer barrel life. Of course all of those vary widely, although you can get the same types of barrels in both calibers, the bullets are generally of the same construction (gilding metal jacket over lead core) and approximate shape (boattail but not an extreme one), and the propellants used are similar to the extent that some like Varget overlap and work well in both cartridges.

In US military applications the 7.62x51 NATO is loaded to fairly reasonable levels while the M855 is fairly hot and the M855A1 is extremely hot. If one compares only the US military fielded ammo, the 7.62 is likely to have much longer barrel life in a given firing schedule. Except that the firing schedule probably won't be the same, since the 7.62 is mostly used at two opposite extremes: DMR / sniper rifle with slow fire of single shots, and GPMG with sustained high rates of fire. Apple meet orange.

[lt1 sport]

I would think the faster 1 in 7 twist rate would have more to do with barrel wear then let's say a 1 in 12 barrel typically used with M80 ball or even alot of 308 ar's with a 1 in 10 twist.

[daddyusmaximus]

I would think that the more expensive .308 ammo would be a bigger worry than barrel life. With the two calibers having different roles (for the most part) any comparison is kind of a non-issue isn't it?

[556BlackRifle]

I would think that the more expensive .308 ammo would be a bigger worry than barrel life. With the two calibers having different roles (for the most part) any comparison is kind of a non-issue isn't it?

Yup. non issue.

[lysander]

With all things being equal (steel type & coating/treatments etc.) which caliber wears out the barrel sooner between the 5.56 AR15 and the .308 AR10? Does one caliber last for higher round counts than the other? I know the .308 is obviously a bigger bullet but I've also heard that the 5.56 has greater chamber pressures, so does anyone know which barrels wear faster/last longer (all things being equal).

All things equal in the barrel make-up leaves the barrel life to the propellant flame temperature and pressure of the ammunition as the governing factors, with flame temp dominating.

Since .308/7.62mm and .223/5.56mm use similar burning propellants and have similar chamber pressures the barrel lives are similar.

Note the changing of propellants can result in a change in barrel life of 8,000 to 10,000 rounds.

EDIT: The 5.56mm does not have a significantly greater chamber pressures than 7.62mm, less than 7%.

[HelloLarry]

Experience from HP competition indicates that .308 barrels last longer.

Want to cook either caliber barrel quicker? Use a hot double base powder like N540 and the heaviest bullet you can stabilize or a steel jacketed bullet.

[lysander]

Experience from HP competition indicates that .308 barrels last longer.

Want to cook either caliber barrel quicker? Use a hot double base powder like N540 and the heaviest bullet you can stabilize or a steel jacketed bullet.

Competition 5.56mm usually uses hot, high pressure loads with heavier bullets.....

[Spin Drift]

I typically don't get a .308 as hot as a 5.56.

The 5.56 is gets shot pretty hard, up close, fun and games.

And what's o.k. (accuracy wise) in a 5.56 may not be o.k. from a .308.

I had never considered gas blow-by in a boat tailed design, but sure, makes sense.

I'd love to see if I could wear out an ACC! 10k of M80 would get me started...