AFAIK except for Swiss black powder, Pryodex P produces more velocity from revolvers than an equal volume of the same granulation of all the other black powders. That serves to illustrate how every powder has some advantages and disadvantages.
I measure out the powder charges beforehand and store them in medicine bottles. Then pour the powder into the chambers with the help of a small funnel. But I do load the cylinder off the frame using a loading press which provides easier access for the funnel.
Some folks buy narrow capped vials or tubes for storing their powder charges in which might make it easier to pour powder directly into the chambers than with medicine bottles. The tubes come in different lengths too.