Roy, When I measured the chamber length before I was guesstimating with a 6" scale. When I measure with a proper tool it comes to 2.675. A fired modern 2 3/4" shell comes to 2.655. So, it must be made for 2 3/4 in shells. I've crawled all over this thing with a magnifying glass and can't find any markings as you describe. There is a tiny mark on the fore end lump, but I can't make out what it is. It shows in the first set of pictures.