The problem that arises with this is that - and you'll have to forgive my less than patronising almost to the point of insulting view, so sorry before I go on........... for the average enthusiastic amateur, bless 'em, is that you get the '.......all the gear and no idea syndrome'. You know......... full set of gauges and all the tools and all the......... you get the idea....... When all you need to know is that the rifle is accurate. And when the accuracy starts to drop off, THEN you start to investigate, starting with the bleedin' obvious.
Here's an example...... During the era of the No4, we had all manner of bore and body gauges. In fact, the Chief Examiner had a whole inspection tray full of them plus the others for this that and the other. So a good accurate No4T for example would come in with what looked like an area of corrosion or pitting or whatever that was proving a bit tough to scrub out - only to find that the XY gauge would enter more than Z". So on that basis alone, the rifle would have the barrel changed - and when that happened, maybe it couldn't CHS and so it'd be ZF'd. We've all seen barrels as bald as a badgers ars........, er....... bottom or shining like a sewer pipe and wonder how the xxxx the bullets get out of the end. And we've all seen almost new L96's that are simply incapable of grouping
Those days are GONE.............. Now, the criteria is 'does the GO gauge run freely?' If so, 'does it pass the accuracy test?'. If it does, then that's the end of the matter. But for a sniper rifle, we let the final arbitrator be the sniper. I suggest that this is the criteria you stick to.
I could be wrong of course