Throat erosion and Muzzle erosion

[JP1954]

I have read several posts in various places talking about these two issues often in the context of evaluating a rifle prior to purchase. I am currently looking at some M1 Garands and M1 carbines. I would like to add one of each to my small firearm collection. I am guessing that throat erosion is probably measured in the chamber where the bullet is positioned at firing. And obviously the muzzle erosion must be the measurement done at the muzzle.
Can anyone tell me how to make these measurements? I suppose I will need to acquire a tool for making the measurements and I will also need to find out the sprecifications of the bore for each of these firearms. Any help with any of the above would be appreciated.

 

[30Cal]

There are two gages that you use. One is a TE gage, the other is the MW gage. Lower numbers are better. 10 on the TE would be reject by arsenal standards.

Muzzle wear is caused by sloppy cleaning. The USGI 3-piece steel cleaning rod has ruined more barrels than anything else IMHO. As far as accuracy goes, it's much more important to have a good muzzle. MW2 or better will probably make a good shooter. If you stick an M2 ball cartridge in the muzzle, you are looking to see about 1/8" of copper ("the bullet test"). If it drops into the shoulder, then it's pretty well worn.

 

[Jim K]

A more valid term is muzzle wear. There is no erosion at the muzzle because the propellant gasses have cooled too much by that time to cause erosion. Muzzle wear, however, will be uneven. That means that the bullet, exiting the bore, will not be released evenly all around the bore. Gas will try to escape on the side that is released first, and that will tip the bullet in the opposite direction. The result is a very inaccurate rifle.

Throat erosion occurs at the mouth of the case, in the area known as the barrel throat. That is the area in which the bullet sits when an unfired cartridge is in the chamber.

As soon as the cartridge is fired, the case neck opens up slightly, allowing hot gas to rush past the bullet, which tends to stay where it is due to its own inertia. That hot gas, confined to a narrow space, moves at very high speed and acts just like a cutting torch on the barrel steel, resulting in throat erosion. When/if it gets bad enough, the bullet tries to move into the rifling at an angle, skidding and being distorted. The result is inaccuracy.

However, even if TE becomes very bad, inaccuracy cause by erosion will not be as bad as inaccuracy caused by muzzle wear.

Jim

 

[1911Tuner]

Wear

Excellent description from Jim Keenan. A point to make regarding muzzle wear. Severe wear at the muzzle and crown is most often caused by improper cleaning and contact between the muzzle and cleaning rods. Most of the damage is within the first half-inch or so and very often a lot of accuracy can be restored by parting off the damaged section and recrowning.

 

[JP1954]

Thanks for your input. I found a carbine that looks pretty good. I inserted a 30-06 cartridge (I didn't have a 30 carbine one) into the muzzle and it had about an 1/8inch still showing. I also looked in the breech with magnification and it does not seem to have much wear. I forgot to bring a dental mirror with me so I couldn't see the throat.The bore looked good too although there was grease and dust in it which made it hard to see with great detail. I was able to clean out about a half inch deep into the muzzle with a small piece of cloth and bic pen and the lands look fairly well defined. My only concern about it is that the breech seems to be somewhat loose in the stock.
Is that common in these guns? Could it be shimmed up a little?

 

[Jim K]

Throat erosion is rarely a problem with the carbine due to the lower pressure and the type of powder used, plus the design of the bullet and the throat.

Muzzle wear, almost always due to using a cleaning rod, is also usually less of a problem because all U.S. carbine ammunition was non-corrosive, so a lot of scrubbing was not necessary.

Jim

 

[JP1954]

Thanks for the input on the carbine. I'm now looking at Garands. The 30-06 cartridge I stuck in the muzzle left about an 1/8" showing on one of the ones I looked at and about 1/16" showing on a second one I looked at. Obviously the second one has more muzzle wear. That being said, can someone tell me if that would be considered a lot of muzzle wear?