I am currently working with an original Sharps Bridgport rifle trying to work up an accurate load. The gun still has good rifling and very little pitting, but it will not shoot any of the lead cowboy loads. When I did a chamber cast i found out why... The gun is marked 45 2 1/10 Sharps, but a chamber cast show that the gun is chambered for 45-80 in a 2 1/10" case. The throat is so long that a 45-90 will almost fit. So far the best accuracy has come with a 500 grain paper patch bullet wrapped with 2 turns of Buffalo Arms patching paper. Final diameter is 459. The patches are lightly lubed with tallow and bee's wax and a 1/10" cookie of lube is seated under the slug. This load will group 3 shots into 3" at 100 yards with the factory ladder rear and silver blade front sight. The sights leave a lot to be desired for my eyes, but for some strange reason the owner of the gun won't let me change them. After 3 shots the groups open progressivly unless i run the Fischer cleaner through. When loaded to best advantage the paper patch just lightly engraves the rifling. I am loading with 75 grains of Swiss FFG dropped from a tube and well settled and am using milk carton wads between the powder and the base of the buller. Thihs keeps the lube from contaminating the powder adn from sticking to the base of the bullet. Tails are tucked into the base of the bullet. My patch template came with the gun and is a two wrap.
Now the funny thing is that the chamber looks a LOT like the IAB chambers, but not quite so long. I wonder if they got a P/P 2 1/10 rifle for a sample.