11.3 x 50/51/52R Beaumont

I have seen references to:
11.3 x 50R Beaumont, case length 1.97"
11.3 x 51R Beaumont, case length 2.02"
11.3 x 52R Beaumont

Are these really different cartridges? If so, why would they have made them so similar? I have a cartridge labeled 11.3 x 50R but I measure the case length to be 1.91"
Thanks,
Joel