Greg, good advice above. Back in the Dark Ages, before I know what I was doing with vintage doubles, I had a prewar Sauer 16. I had the chambers lengthened to 2 3/4" and shot high brass American pheasant loads in the gun (3 1/4 DE, 1 1/8 oz). Those old German guns are hell for stout and it never shot loose, but I wouldn't do it again!
On the subject of "standardization" at 2 3/4", the 2 1/2" load remained the "standard" in British and European game guns before WWII, and in most countries even for some years after the war. Even in this country, although we were pretty much standardized on 2 3/4" for 12's, 16's, 20's and 28's before the war, all the gunmakers did not make the switch at the same time, nor did they all switch all the gauges at the same time. Elsie 16's, from what I've seen and read, were perhaps the last guns converted to a standard 2 3/4" chamber. I've found Elsie 16's made as late as 1939 or 1940 that still had 2 9/16" chambers.
