Do you remember any of the particulars on the accident? Such as powder-ball-lube or powder-wad-ball, or black powder or substitute, etc. If an accident is possible (that is, such has occurred) then it is worth the extra second to use a measure. If I go that route I think I'll still use the measured- measure on the flask and pour that into a bigger than needed measure so that I don't lose any of the powder, and then pour the charge from the bigger than needed measure into the chamber- probably possible to come up with some special design just for a percussion revolver.
And....do some flasks have a better cut off system than others? What I am getting at is I wonder if a cheap flask has more gaps, etc to cause the flask to explode if a flash of flame is present. Do the better flasks have a tighter fit, etc to help ward this off? Just wonder'n