In truth, you don't need a gauge to show barrel wear. The only test you need is an accuracy test. That way, even if a barrel looks absouletly worn out, if it shoots accurately, then who's to say that it's worn out. By the same token, a barrel that is mint and pristine and conforms to every gauge limit can sometimes shoot like a pig. And to be brutally honest, in my opinion as a bit-part Armourer, I'd say that NO test was better than the nose-of-a-round-in-the-muzzle test you speak of!