I gotta laugh, my buddy was one of the most active reenactor & living history participants that I have ever known, which is saying something. Ranger Jim Lewis at Stones River did make him clean it, mostly because Jim couldn't stand the idea of leaving a musket dirty. Was it actually ten years between cleaning? Who knows, but his ramrod did ping every time, so maybe cleaning up after firing blanks isn't as important as we might think. I have never made the experiment, myself."Firing blanks fouls the bore, but doesn't affect reenacting. One of my friends claims he hasn't cleaned his musket in ten years."
If your friend is telling the truth, he doesn't really reenact as a CW soldier. No reenacting officer or sergeant of any worth at all would allow such a weapon to be used. We check before the first battle of the weekend, and when there is no 'ping' at the bottom of the barrel by dropping the ramrod a few inches onto the base of the barrel, that soldier and his musket are sent to clean it, not allowed to stay and march off to the battle.