I didn't know Lyman made a .56 smoothbore GPR. I know Thompson/Center used to make a percussion Renegade in .56 smoothbore... I have one. But Lyman?
Out of curiosity, I went to the American Single Shot Rifle Association "For Sale" forum to have a look, but couldn't find the gun in question.
Maybe a little tangential, but I've always wondered why T/C didn't make that Renegade smoothbore in .550", which would be a true 28 gauge, instead of .56 caliber. That would have made it a lot easier to get wads and other supplies that fit properly. I'm sure they had a reason.
Notchy Bob