Not disagreeing with what you say at all. The point is though that just the fact it has 16 in a circle does not itself indicate a 65mm chamber, this was the original statement on this. It is not that mark which indicates the 65mm chamber, but the lack of any 70mm marks would. On my VL&D/J P Sauer one has to look at the extractor to determine it was/is a 70mm chamber, simply looking at the under bbl marks do not in any reveal it, & it has 12 in a circle.
PS; 2 9/16" (65mm) was standard in the US as well for many years in the 16ga. In fact the 16 was the last of the gauges other than 28 & the .410 bore to standardize on 2 3/4". Never-the-less I have a 16ga Lefever made between 1907 & 1915 with 3" chambers. Can't prove if they are original or not, but the highest probability would say they are, as 3" 16's have never been very popular, but were available on order at the time this gun was built.
