[kkfx]

People do not know much about old cartridge powder measures though :D

[ndsipa_pomu]

"Grains" are still used for measuring out powder/chemicals (also arrows). If I saw "gr", I'd interpret that as grains rather than grammes as "g" is definitely grammes, so the extra "r" must signify something.

[antonkochubey]

Air rifle bullets are typically specified in grains, for example