I agree that it takes some practise and the correct size of the measure to get BP stricken loads within acceptable variations. I've foud, through trial and testing, with a measure with approximately a .45" hole or slightly smaller, stricken measure can be held to 1gr. variation, that being 1/2gr. above or below. That small amount seems to have little or no effect on achieved ballistics, especially when a filler is used.
: There are few powder measures that are safe to use with BP. Lyman not has one, and there may be others. Generaly, an aluminum powder chamber with a brass drum in iron base is required, as the plastic powder vessels builds static charges which can be very dangerous.
: One must pick a powder, weight what the measure throws and above all, be consistant. Consistancy is almost 1/2 of BP accuracy.
: A good lube is also needed for BP ctgs. I think that OxYoke hollow stick yellow bore butter lube is probably good, as is SPG and Lyman BP lube. As wel, Beeswax/Vaseline, in a 60/40 mix also works well.