Headspace Gauge vs Erosion Gauge

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.