OK needs some input on some long term tooling acquisition. Recently bought a couple of Milsurp Rifles at auction and once I get them home I want to check them over a bit before shooting them. I was looking around at getting either Headspace Gauges or some Erosion Gauges to check out the barrel. I was wondering what would be a better investment since both can get kind of pricey depending on what you get. So by all means please educate me on the positives and negatives based your experiences.
They are both important tools for different reasons. Unfortunately most of these tools are for 1 caliber only so it can be expensive to buy them for 1 use. If these guns were from the CMP they were measured before being sold.
Thanks. The guns in question came from an auction. At some point they might have been CMP guns, I’m not sure. Maybe once I get a picture of the S/N’s and send a FOIA request I can always see. One’s late build 1903 the other a 1917. Am I better off find someone that has any of that or gunsmith? That’s kind of why I was debating it as I’m not sure when I’d use them again.
Headspace gauges will tell you if a gun is safe to shoot. There are basically three gauges. GO, NO-GO, and FIELD.
- GO is generally used when building a rifle to make sure you have enough headspace. The bolt will need to close on a GO gauge.
- NO-GO gauge is the maximum headspace you want to have. An in-spec gun will not close on a NO-GO gauge. A gun that barely closes on a NO-GO gauge is reaching or is at end of life and accuracy will likely suffer.
- FIELD gauge shows you an unsafe gun. If a bolt closes on a FIELD gauge, it should be considered unsafe and not shot.
Erosion gauges will tell you how accurately it’s going to shoot (roughly speaking). For that you have throat erosion gauges and muzzle erosion gauges. A gun that has a 0 on an erosion gauge is new or close to new and has plenty of life. A gun that is a 4 or 5 on an erosion gauge shows a LOT of wear on the rifling and will not yield particularly good accuracy.
Muzzle erosion gauges are specific to a bore diameter. So a .30 cal. muzzle erosion gauge will work on both an M1 Garand in .30-06 and an M1A in .308. Throat erosion gauges are caliber specific.
On the other hand headspace gauges are chambering specific (i.e. .30-06 only) and are cost-prohibitive to many. I keep a set on hand for .308 and 5.56 NATO as these are the chamberings I tend to do some gun plumbing with.
If you plan to buy U.S. mil-surp guns outside of the CMP, erosion gauges are a good tool. If you buy them direct from the CMP, they’ll come already gauged.
Thanks Candyman, much appreciate the breakdown.
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If you can’t buy both get the muzzle erosion gauge. Of the two that’s the more Important one versus throat erosion…
Headspace gauges aren’t cheap.. find a friend that has some and borrow them…