Sorry I wasn't clearer in my analysis. The Russian cartridge does have a slightly larger ID in the powder chamber but mainly the larger footprint of the rim serves to more widely distribute the load over a larger area of the breech face. Similar to a woman's stiletto heel versus a wide wedge heel, the load of the 30-06 is concentrated on and transferred by the smaller case head area while the larger rim area of the Russian case will tend to 'float' more on the breech face. The force differential is negligible but it's still there. This somewhat confuses the issue but I still hold to my opinion.
This is a gray area in my mind, i.e. the actual force exerted upon the breech face by different-shaped cartridge cases is difficult for me to evaluate precisely. The initial tendency is to simply use the cartridge's internal powder chamber floor area in a straightforward calculation of straight-line rearward force, but to me this is misleading. The total rearward force is also increased by the curved shape of the internal powder chamber's floor-to-wall transition which applies more force in an ever-decreasing manner as the radius increases beyond the powder chamber ID. IOW as the force vector gradually changes from rearward to sideways, the additional rearward force is gradually decreased as the angle changes and the area widens.
Then there's the question of case taper, chamber wall surface finish, presence of oil, brass hardness, etc. Been a LONG time since I had to use the calculus I learned oh so long ago and I've long since erased my memory tapes so I quit calculating(grin).
My old Physics prof is a shooter and is still kicking, guess I should call him!
Regards, Joe
