In my opinion, I think they were still loading directly from the horn back in the 1840's, however, you could hollow out a few antler tips in various depths and scrimshaw them with the capacity, like 70 grains, 100 grains, ect, then string them on a leather lace...
I have a deep antler tip with different levels scribed on the inside of the cavity, this works as an adjustable measurer so to speak, I just fill the measurer to the desired level line...
I would suspect this would be more accepted than a commercially made adjustable powder measurer, although I am not really sure of their start date...