In my humble opinion the only acurate way of confirming a chamber depth is to use a plug gauge.Turned up to approved British proof size. Others have disagreed with me on this. I could not see to well on the photo ,but it would appear to be black powder only.What are the rest of the barrel dimentions.
That may well be right if you deal only with good quality British built guns. Throw in a good mix of both Continental & American ones & I can "Positively Assure" you it is not the case. Not all makers used absolute British specs for minimum chamber size. If I recall correctly British specs call for a minimum chamber dimension of .800" (12ga). Drawings for the American L C Smith for instance show a dimension of .798" (12ga). With a taper of .005" per inch in the chamber walls a.002" smaller chamber dimension than the plug will stop it more than 3/8" short, .400" to be exact. In this case the 6" flexible scale 8-Bore cited is much more accurate. In spite of the fact I have a nice set of gages I turned up myself to SAAMI spec size I encountered enough pre-SAAMI guns having chambers a thou or two undersize that I seldom use them anymopre, relying instead on that Starrett 6" scale.
