Somewhere in the north woods of Wisconsin is a .348 round and in the Orogrande mine in New Mexico is a few 357 mag cartridges. Couple of my belts have loops and the bandoleer holster rig I am making will have loops for 44 mag and 20 gauge shotgun shells but other than that all rounds for whatever weapon I am carrying goes into my right front pants pocket and nothing else goes into that pocket.
I hate losing rounds and loops have always been a pain in the yup-yup to get out in a hurry or when I was in certain positions like the close quarters of a blind. Just dos centavos from an old dinosaur. Exception is rounds that fit into a magazine and they go in a pouch.
Just personal experience but other than cowboy movies I don't remember any duty belts from the late 40's and early 50's with loops.
Good intentions will always be pleaded for any assumption of power. The Constitution was made to guard the people against the dangers of good intentions. There are men in all ages who mean to govern will, but they mean to govern. They promise to be good masters, but they mean to be masters.