this site is usualy good but completly wrong here
10x60 R Express/ .450-.400 Express 2-3/8" / .400 Express / DWM 76 / DWM 96 / GR 127
DWM 96 / GR 127 is the 11,6x60R 450 express, short version of the 450 BPE 3,25"
.450-.400 Express 2-3/8" , british mother of the 10,3x60R Swiss
.400 Express, common designation for the long Purdey round
10x60 R Express, 10x60R 400Expess would be the right designation but the measurments on this site are for the 11,6x60R 450
I dont see till now another maker and it seems that the 10x60R 400 was only made from Georg Roth in Austria
case number GR 143
bullet number 589
the fact that was ever made with the lead bullet makes it clear for me that this was only loaded with black powder. production of this round may stop with the outbreak of WW 2 in 1939 for ever but it was a very obsolete cartridge in this time also.
you see here 11,6x60R 450 cartridges