That's exactly what I was worried about, the powder chamber vs loading from the muzzle. I probably should have hit more on that thought/worry from the beginning. What if I were to try a different powder such as FG and maybe be able to fill the chamber a bit more? Recipe for failure? Wonder if roundballs would work better at close range? (Twist?).The powder chamber in a Sharps is rarely filled by paper cartridges, it's larger than you think and will take a pretty large charge to fill it. If you don't fill it and then ram a bullet down from the muzzle and into the chamber cockeyed you're really going to have a problem. I'm sure your county LE are no dummies and it's pretty well known that once a breechloader always a breechloader. Like on AR15's, once you register a lower as a pistol lower it will always be a pistol lower regardless of what you put on top of it.
I don't know why you guys are so hung up on the "legalities" of a breechloader. It's not like I'm trying to export or import the rifle. The law just says "Muzzle Loading" and that's it. My neighbor hunted for years with an 870 w aftermarket blackpowder barrel. I've hunted with 700UML rifles, etc. Both are modern arms that require a 4473 and are considered breechloaders by federal law. A "converted" sharps would be no different so long as I can only load it in the field with a ramrod.
I'm away from home until tomorrow so I haven't been able to try anything yet. I feel like I've gotten some good advice/imput here already though.