As for me, I just like the look of 30 deg shoulder and there are many more "target" cartridges with that angle, over the 40 deg one.

If there is any turbulance associated with the flow of gases going around the corners of the shoulder in the cartridge case, the 30 would be better than the 40 for that, also.

Frank

I once sold an m-92 Winchester Mashburn Bee with the 30 degree shoulder that shot nice, but the loads were hot enough to push the ejector into the breechblock.  Jerry Yorks, of Newaygo, Michigan built it.  Jerry was a real hi-velocity man.  I liked the caliber so much, that I had a new Marlin 1894 in .357 re-barreled to 22 MB, but the reamer they used was not only 40 degree, but the neck was so short as tobe non-existant.  It was not satisfactory to re-load.    Too bad as it is a little beauty, half magazine, 24 inch barrel.  Shoots factory loads well, though.