More research

The .450 Nitro Express 3.25 in (83 mm) was the first Nitro Express, developed around 1898 by John Rigby. This cartridge was based on the then popular .450 Black Powder Express case with 70 grains (5 g) of Cordite and a 480-grain (31 g) jacketed bullet. Muzzle velocity is listed at 2,150 feet per second (655 m/s) with 4,909 ft·lbf (6,656 J) of muzzle energy. This straight case has a length of 3.25 in (83 mm) with a .670 in (17.0 mm) rim. [1]

Early cartridges used the black powder case that was designed for around 11 tons of pressure per square inch and not the 17 tons of pressure that the Cordite load generated. Case extraction was difficult, especially in warmer climates such as Africa and India where the cartridge was primarily used. To remedy this problem, a reinforced case was produced and Kynoch made a reduced load to lower the case pressure.

Now more thoughts
Since this is a tapered case, if the shell holder were shortened so the case could enter the die more, would this assist?

Mike

USAF RET 1971-95 [Linked Image from jpgbox.com]