I've done some research in a reenacting forum discussion about the legality of "defarbing" your musket or other blackpowder arms. It seems to me a little personal knowledge could go a long way defending the legal ins and outs of doing this.
My original discussion was deleted from the forum where the discussion was being held, I'm sorry to say. But the CW-Reenactors forums have the sideline discussion I started to flesh out my knowledge of the subject. Warning - it's a little thick and drifts to other gun-related issues, but it's a worthy read.