How to tell if an m1a barrel is shot out?

[madd0c]

Any way other than with an erosion gauge?

I bought a used m1a from a friend who I trust takes care of his guns.

My problem is that after about 500 rounds through it, I have come to the conclusion that it is a 4-5moa gun at best. I have tried factory Federal gold medal match, hand loads with different charges of 4064 and weights from 145-175gr and still no luck.

I have a smith enterprises mount on it, with a nightforce 3.5-15 taken off a sub moa rifle. So it is not the scope. The mount is a very solid 3 point mount and the scope has not moved any in the rings (I mark scopes with a grease pencil when I mount them new to see any shifts)

After these dissapointing outings, I broke down and REALLY cleaned the barrel with a hoppes9 and kroil mix and 60 strokes of a GI issue brass brush. I got the barrel white patch clean and got tons of stuff out of it, gave it one more shot with gold medal match and still the thing from sandbag bench will not do better than a 5" group at 100 yards.

The rifling in the barrel seems very shallow to my inspection with a bore light.

Could this barrel be shot out?

Thanks for any info,
madd0c

 

[nicholst55]

Yes, it could be; however, there are any number of other things which could contribute to the lack of accuracy. Fit of the stock, barrel crown, flash suppressor too loose/tight, no pressure on stock ferrule at front band, etc. Maybe the gun just doesn't 'like' Federal GMM ammo.

 

[buttrap]

well a M-1 is not a target gun to start with the service spec on the things was 3.5 inch new and 6.5 before it was thought to be out of order or pits in the bore that exceded 1/8 inch.

 

[BADUNAME27]

Get a powerful light source and illuminate the barrel right ahead of the chamber. If the throat is badly eroded it'll have the appearance of a dried out mud puddle. you'll see cracking or a "frosted" look. It may also take on the appearance of the crescent moon from the 3 to 9 clock position.

Last, shoot it. If it's minute of impact area then chances are a number of things are wrong, to possibly include the barrel.

Good luck.

-C

 

[Lee Roder]

If you don't want to spend the bucks for an bona fide erosion gage, individual pin gages can be had quite cheaply and can tell you the same thing, or even more about your barrel.

 

[madd0c]

Lee,
Could you explain the pin gauges for me? That may be something I am interested in doing.

Thanks,
madd0c

 

[Lee Roder]

madd0c.

Sure, check out the thread over on the CMP forums entitled "Why I No Longer Trust a MW Gage" for the basic idea

http://www.thecmp.org/forums/showthread.php?t=5392

I'm not familiar with the .308 caliber per se, so I won't tell you what size gages are appropriate for you. You will need to research your bore's specs to determine what's "out of spec" for your bore. Then you can choose the most appropriate sized gages to characterize the state of wear inside your bore. For an M1 carbine, a complete set of gages cost me less than $15. Depending upon how precisely you'd like to measure the pattern of your bore's wear in the round, you might get by with much less, or more.

A series of pin gage measurements can provide a much fuller description of wear (belling) over the length of the barrel than a single throat or muzzle measurement at each end. It can tell you whether counterboring might be appropriate for example and how deep to go.

Good luck.

 

[61chalk]

Dude....take your 308 bullet an stick the bullet into the muzzle....where does it
stop at? If it reaches to the brass its shot out...if it stops about 3/16 of an inch
before the brass its around 2.0 which isn't too bad....this is done on Garands, an
should be the same with your rifle.

 

[nicholst55]

this is done on Garands, an
should be the same with your rifle.

Except he'll have to remove the flash suppressor first. It also won't tell him a thing about throat erosion.

 

[madd0c]

I don't mind removing the flash supressor, and will give this a try. Also am figuring out the pin gauge diameters I need so I can check the throat area.

Thanks,
madd0c

 

[Lee Roder]

Oh yes, re the pin gages. There's two gage variants in every size, plus or minus, literally, just to confuse you. You want the minus sized gage in whatever nominal diameter you need. It's explained pretty well in the thread

Also, re the bullet test, just because the first 1/4" of the muzzle bore is a bit oversize doesn't mean the barrel is "shot out" and is scrap. Removing a bit of rifling there might be all you need to get you back to "like new"

 

[61chalk]

"It won't tell him a thing about throat erosion." Never said it would did I.
Was responding to his title. Throat erosion isn't the only thing to look at..if
you can drop a bullet down the barrel an its still accurate you've got yourself
a heck of rifle. Hope you find the problem an can solve it maddOc.