Ft.Frederick market faire, Jason Gatliff on suttlers row ( the historical trekking mag. fella) I picked one up from him to measure loads for un-mentionable BP cartridges. they are accurate in measurements and not all that expensive. The opening on the measure works very well in cooperation with a drop tube, never used it for a BP muzzle loading rifle but I see no reason that it would be hard to charge the measure from the horn.