Larry,
I have a couple of different chamber measure gauges, both came from Brownell's, if I am not mistaken. Geoffroy Gournet has warned me about using SAAMI spec tools on French guns, point blank telling me they are not reliable for determining chamber length.
Gene has found a bunch of old guns, marked with eye opening chamber lengths, under French proof laws in effect at the time they were built. I've not had the chance to observe anything but 6.5, 65, 70, and 76. I wish I had a buck for every French gun I've seen that had 65 stamped on the flats. Most of them are.
Having said that, if I came up with a cool French gun, of any sort, that was around 6 pounds, proofed in the first half of the last century, and marked 76, I sure as hell wouldn't run down to the 'mart and buy a 3" load to try the old girl out with. From where I stand today, light loads make sense, especially in an old French gun. I suppose you could add Italian, Spanish, Belgian, Prussian, or, whatever, but, those guns, in that age catagory, are pretty far out of my wheel house. But, it would make sense to be cautious with ammunition for them as well.
I've also come to a point where, for my own use, if I look at a French gun that is marked 65, and say, 18.2 on bore, I expect it to still be there before I part with MY cash for the gun. I have owned, and continue to own guns that are modified in that way, but, I'm done BUYING any more like that.
For what it is worth, the beautiful R16 12 magnum that was here all those years, never saw a 3" round.
Best,
Ted
