Thanks, 1878. I know there are multiple issues here. Have also noticed that the rimmed versions seem to be loaded lighter, but wonder if that is just a cautious approach by the loading companies who suspect that there may be some very old (and some very cheap) break open actions out there.
Hard for me to understand why the rimmed case wouldn't transfer some of the thrust laterally thru the rim to the receiver face, since there must be SOME motion by the case. (In the "perfect" case and action there wouldn't be, but in the real world both do move at least fractionally. Or why would we resize?).
What got me thinking about these issues is a new Savage/Valmet combination gun in 12x.308, and reading discussions about appropriate .308 handloads for it....and shooting a friend's Merkel 16x16x7x65R, basically a rimmed .280.
