Then you have the subtle differences between IMR-4895, H-4895, and A2495 (some weird history on why they called it 2495 instead of 4895, halving the first two digits). Some will say that today's IMR-4895 is still the original M2 recipe, but there is dissension in those ranks.

The problem with H-110 is that you are strongly advised to not "light load" it. Not that you would do this with a M1 Carbine anyway (wouldn't cycle).

I have a .44Mag lever action and have been toying with the thought of a Ruger six-shooter in the same chambering. If I want to light-load .44Mag for revolver shooting or lever-action shooting for kids/ladies, then H-110 is a non-starter. For that, I bought A4100.

Coincidentally, A4100 also works well with .30 carbine, as it is "near compat" with H110.

Of course, all recipes need to be dialed in carefully with testing.

Also, I thought WC820 was the original M1 Carbine powder.