The similar gauge for the Vickers is measured from the visible breech face and registers leed wear for remaining barrel life in OHF or Overhead Fire guns where a few rounds dropping short could cause, er......., problems! It was not designed for the rifle but I dare say that the inspectors/viewers/examiners would use one in a borderline case. Once the leed starts to wear with boat tailed bullets, there's no set-up and the gas wash past the bullet really accellerates fast. It doesn't take long to go from 1st quarter of life rapidly downhill
Sorry for going off on one of my tangents......
But to be brutally honest and frank, the worst thing you can give the enthusiastic amateurs is a load of gauges, believe me............ Take CHS gauges for example........ Oh dear....., you've got me going again....... Give one of these EA's a set and he's changing the bolt heads and testing for this that and the other and buying different sizes and....... But nobody told him that the 'sizes' are really all over the place. And even worse is when they get their hands on the 'so called' muzzle wear gauges. Jeeeeees, at that point they are immediate experts. Right....., I'll stop now; I promise!
Sorry, can't help myself but don't |EVER give one a striker removal tool. Or if you do, make sure that it's made of plastic!