What firearm(s) are you intending to feed?

If it's the Mannlicher Schoenauer M1910, you do not want the .375 NE 2.50", as the MS is 2.25".

The proper cartridge for an M1910 MS went by many names, including 9.5X57, 9.5X56, .375 Nitro Express, .375 Nitro Express Rimless, .375 RNE, and more.

The 9X57 is a different cartridge which does not interchange with 9.5X57, though when I ordered my RCBS dies about 1990 they came to me in a box marked 9.5X57 MAUSER. I phoned RCBS and was repeatedly assured that they were the proper dies for my M1910 - they were, and make perfect replicas of DWM 531 with proper neck and shoulder dimensions. Brass formed through them from fresh .35 Whelen ends up a bit narrower than spec. toward the base, but fireform just fine.

If you're feeding the M1910, you want a RIMLESS, non belted (no Velopex) .375 (9.5mm) by two and a quarter inch (57mm) cartridge.

Proper dies for M1910:

A cartridge from Reed's Custom Reloading (Oklahoma), one of my old handloads, original DWM 531, fired brass from my old handload. My handloads from fresh .35 Whelen, Reed's from new Norma 9.3X57 drawn straight, then formed.

Proper dimensions of 9.5X57 / .375 Nitro Express Rimless 2.25" :

The 9.5X57 and .375 RNE 2.25" are identical in every respect except for the propellant load of original cartridges, which was two grains lighter on the British (RNE) load. Some speculate that this was to compensate for the African and Tropical climates often encountered by intrepid British 'traveling sportsmen' and professional hunters:

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