I've wondered that with smaller bores, but shooting sabotless, ie the 375 and 40 cals, if the long, thinner powder column might be better shortened and widened also. The efficiency seems to increase with squatty type cartridges - 6PPC,the BRs,308 vs 30-06(80% the powder, 95% the performance),Rem Ultra-mags and all the Win short/ss mags. I'd like to see a chamber under my 40 with a 35 degree shoulder angle that would hold appx the volume of 50-60 grains of whatever I'd like to use, such as 60g H-4198 with 200SST or 63-64gs of same with 175 Barnes. Would need to get a measure of the volume and never load much under full capacity and don't know how over-loading would do. I think as the columns of powder get longer and thinner, not only less barrel length will be available but suspect efficiency will go down. Will likely use a little different speed of powder in 40 over same bullet in 45. Will probably be close and maybe the same. The long column , I think, would lend itself to a slower powder, but trying to keep powder volume down encourages faster powder.