9.3 - how'd that #5 shoot? Seems to have worked on that bear.

The .375 calibre on the .303 case leaves just a tich of a shoulder, while necked up to .40 takes it out to a straight taper, no shoulder - .40/60 Maynard being that calibre's name on those ctg. dimensions, I think, IIRC.

There is such a sloping taper on the .303 case, that improving them, aka Elwood Epps shop in Ontario, Canada, makes a worthwhile increase in capacity and speed. I was in Elwood's store in about 1968. At that time, I was in a speed-freek funk & not interested in big bullets. By age 20(2 years later), I'd changed my mind on bullets and calibres.

The 45,000CUP or 50,000PSI(.303) rating for that #3 allows for quite descent .45/70 or .45/90 ballistics. In the .45/70 and .45/90, the CUP and PSI #'s are virtually identical numbers.

The 2.4" case of the .45/90 should get 400gr.RN, FP or Spitzer old style Barnes doing about 2,300+ & absolutely polax hogs, black bears, moose, elk and deer.

That case is only .1" shorter than a .458 Win Mag and has just about identical capacity. The magnum case has a higher web, shich reduces the capactiy to about the same as the 2.4" .45/90. The .45/90 brass is stronger that any pressures any rifle will handle, so there's no problem in that respect. the .45/90 makes for a very interesting #4 or #5 Enfields, with their even higher strength ratings.