JC,
Pin gauges can also be misused. If they are not presented precisely "square" to the bore the mechanic may think that one that actually fits is too large. The old German proofs used them to determine bore diameter, with their gauges being in .01mm steps. A barrel then marked 7.7, might be 7.71 or it might be 7.79 and still not accept a 7.8 gauge. Or it might be 7.8, if the gauge was not properly presented, at first.
Mike