Yes it is authentic, was "common" tho dangerous, and could be done with smoothbores and eventually Minie-ball loaded rifles if reasonably clean. However, when I say common it was only done as a last ditch effort. It destroyed the gun, as you might imagine, and if you did that under normal circumstances you'd pay dearly. The real trick that was added to flints was to enlarge the touchole -- the "tapping" was not just to have the momentum of the ball ram the gun for you but to dribble powder into the pan.
Alden
Alden