Who knows how many turkeys have been taken with Model 12s ( and other vintage shotguns) over the years...??.. I'm sure they number in the thousands, if not hundreds of thousands..

If I were hunting with a 12 gauge M12 in 2 3/4" I would pattern several buffered 2 3/4" magnum loads and see what gave the best killing pattern at 40 yards or so..

Loads to start with would be Win XX or Federal Premium loads in # 6 or #4 shot...There are plenty of others to try, also..

Avoid using steel or iron shot loads , since they could damage the choke on an older shotgun..