All

Many thanks, good stuff (especially the greasing of hinges not oiling them). My calculations put the 45/70, 30-06 and 9.3x74R pretty much on a par as far as backthrust.

But, anyway I shuffle it, the 375 H&H Flanged comes out as a marked step up from these.

I note this seems to be reflected in manufacturers offerings with the 9.3x74R often being the top of the small/medium bore actions and the 375 the bottom of the big bore range eg. Merkel.

So we can say that a 45/70 405gn at 1850fps and a 45/90 405gn at 2050fps both generate the same backthrust (all else being equal) as they both are notionally operating at the same pressure with the same case head size?

AR2201
Rumours as to my death are greatly exaggerated