I am shooting out of German pre-war drilling and BBF o/u. Both are marked 65mm and have modern steel barrels. Only the drilling has lengthened forcing cones--don't know if that provides a "fudge factor." Am not trying to run "hot" loads. Both have fixed full chokes. I have many reloaded 2 3/4 16 loads already, but the short chambers just really crimp you on the volume. But I can get 1 oz with standard wads--maybe that is enough, but hunting pheasants without a retriever one wants all the slap-down available. I have not found roll crimps to be shorter in factory slug loads, however. They have to be trimmed back to length. Not sure if 65mm is actually 2 1/2 or 2 9/16. I suppose size 6 shot might fit a few more pellets per ounce. Thanks for all the leads for info. That's what this site does! BTW since these are "shooters" I don't suppose it would be out of line to investigate chamber lengthening. Of course measurements would be required to see if there is enough metal to safely do that.
