John,

The dimensions have been posted somehwere on AR as put out by Hornady.

Basically, it is a rimless case with the same head and rim diameter as the diameter of the belt on belted brass and is 2.5" long.

So basically it is like a 338 necked up to 375 but a bigger diameter case starting at .532 at the base as opposed to about the .511 or so diameter just in front of the belt on the 338 etc. Its case capacity is a bit bigger than the 375 H&H but smaller than the 375 Wby or other 375 H&H Improveds.

Mike