Had an interesting phone call today.

A guy has an 03A3 and says he took it to another local gunsmith who used some sort of gauge to measure throat erosion.
It happened to be a double-ended tool which also measured muzzle condition.

The throat gauge gave a result of '6' while the undoubtedly experienced smith (read: counter flunkie) said anything above a '2' is worn out and trash. It was also reported that the muzzle was worn out as well.

The muzzle being worn may have some merit to it because when I told the guy to put a cartridge into the muzzle, it seems that it sinks a little too far inside, with about 1/8" showing.

This was all over the phone and I have not as of yet seen the gun, but I am really curious about this magic tool that can measure throat erosion.

Any experience with this?

-Spencer

You see the military ones from time to time, in the GCA newsletter, etc.

Brownells sells this one, with adapters to use them in bolt guns.

Sounds like a "sales tool" to me.

http://www.brownells.com/aspx/NS/store/ProductDetail.as...THROAT+EROSION+GAUGE

Bear in mind, though, that the operative word in the Brownell's ad is "comparative". The first measurement on a particular throat doesn't mean much. It's really a tool to monitor the advancement of the throat through the course of the barrel's life.

The use of TE/MW gauges and what the numbers mean is a common question over at http://www.odcmp.org
IIRC a brand new barrel can measure from 0-2 TE, Spec calls for replacment at 6 but the barrel is useable until 8.
Note that the TE gauges are specific to the weapon/chamber, that is to say that a Garand 30-06 gauge will not give meaningful numbers on a 03 Springfield etc or on a 308 Garand or M-14 (and visa versa). This has to do with how the gauge is read.
The MW end is common between the 30cal gauges.

Well, surprised am I to hear such a tool really exists. Now the question is: How does the tool work?

I think I've always been skeptical of armorers tools and such things that can give you concrete answers.

-Spencer

It's a tapered plug, with the wear/erosion numbers etched in. On the MW end the number that's flush with the muzzle is the one used. On the TE end the number that lines up with the back of the receiver ring is the number used (and why you can't use a Garand gauge on a bolt gun). The further in either end goes, the more wear that has occured. Remember that these are designed to work with Mil Spec reamers only.
http://www.scott-duff.com/ShooterAcc.htm
http://www.stoneaxeengineering.com/
http://www.odcmp.org/new_forum/topic.asp?TOPIC_ID=6293

OK, now I see.

Seems to me that this tool would be very unreliable.

I'm sure that every armorer's reamers were slightly different. Conceiveably, if one reamer throats fairly long and another shorter, then they could both be brand new barrels but one would read a 4 and the other a 6.

Besides, it doesn't matter how worn the throat or muzzle is if it shoots good, leave it.

IMHO - stupid tool.

-Spencer

I have had new USGI barrels from the wrap measure under TE 1.0 and run as high as 2.0 for some post war SA from the wrap.

The gauges give a good indication on wear, if a reliable baseline figure has been obtained.

IMHO, muzzzle wear (MW) has to be considered as well when considering diagnosing a barrel suitable for purchase and or installation.

The old "bullet test" with a cartridge is a bit unreliable as well, depends on bullet ogive etc.

The "standard" round to use for this test (muzzle wear) should be an M2 ball round, a good figure to look for would be 3/16 to 1/4 inch of the bullet showing (vs swallowed to the case mouth when inserted into the muzzle).

FYI-I've found barrels that will pass the M2 ball test will fail on a MW gauge (greater than 3 reading).

Bottomline, if the rifle shoots well,a collectible etc go ahead and enjoy it. If your looking for service rifle performance, you may want to consider rebarreling.
hth