In almost 45 years of shooting BP handguns I have never heard of anybody using an over-powder card in a revolver. The wad, for those who use it, is enough for everybody I know.
Is this something that you have been told to do?
Also, please note that the recommended load for a modern .44cal BP revolver, according to all the handbooks, reference books and propellant-makers' advice, is something between 24 and 30gr of 3Fgr or 80% of that load for the propellant that YOU are using, so your particular load is a little on the light side. Still, if you think it works for you, go for it.
Also, please try something for me. Hold the pistol in the shooting hand, and cock the hammer with the thumb of the other hand, rather than with the thumb of the hand holding the pistol. You'll be truly amazed at the difference it makes to your accuracy - you are not changing the grip every time you fire.
But hey, ignore me, what do I know, eh?
tac