If you are shooting a single shot 45-70, you might consider purchasing a "taper crimp" die. You can finger seat the bullets, then run the cartridge up into the taper crimp die. Presto, you have a loaded round! This may not work in a lever gun because of the need for the cases to feed through the action.
The buffalo hunters just finger seated the bullets and might have pinched the case mouth to hold the bullet in. But of course they were shooting black powder, which developes a relatively low pressure.