It's too calibre-specific, because Grizzly MKV is the .50 cal variant of the Grizzly Win Mag. Visually speaking, all the handgun variants generally look like M1911 with longer protruding barrel. Sometimes Girls' Frontline character name should not fully influence how the weapon tag should be named after. This tag should also be usable outside 少女前線 context, but still maintaining technicality while still covering more-specific variants.
For the similar reason we have Mauser 98 tag that covers all variants in general, but not Kar98k.
The Wikipedia page said the following:
and the Mark V was designed to chamber the still more potent .50 AE.