I'll bet that the diameter is small enough. Mine is marked in 5 Gr increments & fits inside a 44 chamber. One small enough in diameter to mark 1 gr will probably fit inside a .36 bore!
(I do wonder how easy it is to fill something that size though, it must be tiny to have enough space to mark 1 Gr.)
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”