The gunsmith's position is understandable. Checking such old rifles with gauges set to modern standards is not only typically a waste of time - it can be dangerously misleading, by giving the user a false impression of safety if the gauge test is OK. Many other things can make an old BP unsafe to fire - deep rust pits, welding repairs, worn/missing pins on RBs and Martinis, replacement barrels with the wrong thread and thus very little bearing surface, chambers drilled right through for scopes...