Been shooting Blackpowder firearms since 1973 and have never, ever, dropped a charge down the bore of a rifle directly from a flask or horn as I was taught this is a BIG no-no I'm a firm believer that one should always pour to a measure and then to the bore. I carry pre-measured charges when hunting. However... I do, as Cayugad mentions, use a flask to charge the cylinders on my BP revolver.

BPS