How does he modify the breach block?
Long post but hope it 'splains why I wanted a Sharps (aside from the fact I just like them)
Both of the guys who do it use a variation of the same method. The sliding chamber sleeve that Pedersoli came out with only works somewhat. The guy who's doing mine makes an entirely new plate for the block and it's machined to accept the O ring mod better than anything any factory makes. He also makes a new clean out screw for the flash channel out of stainless steel and cuts if off to the correct length so the channel is as smooth as it can be in a Sharps. Add some high temp/press grease and you have a dead reliable Sharps that can literally shoot hundreds of rounds without the breech seizing. Now the Good Book says there is nothing new under the sun and if you look at the breech of a Ruger #1, you'd swear Bill Ruger was a Sharps fan.
From there, we use Charlie's Tubes for ammo. They're basically a thin wall paper tube that fit onto the ring tail of the bullet. The bullets are called "Christmas Trees" because the driving bands are three different diameters. Generally, the first band near the nose of the bullet is the smallest and just touches the lands of the rifling. Then next band is close to bore dia. The last is over bore dia and will swage down on firing. The tapered effect of this bullet coupled with an 11deg forcing cone cut at the throat and you have a bullet that is self centering every time in the bore and with obturation at ignition, the seal of bullet to rifling is as good as it gets. The paper tubes are consumed completely on ignition. The tubes are closed at the breech end with hair curler paper which present no barrier to ignition. The tubes are also in various lengths so they will work with different length chambers so the cart will extend to the base of the chamber when the round is inserted. On insertion, the tube will completely fill the chamber to the rear allowing the user to "force seat" the bullet into the rifling a bit before closing the breech. In addition to the forcing cone cut, I'm also having a competition crown put on the muzzles.
There is a phobia over airspace in loading black powder and it is warranted on muzzle loading and brass cart designs. The Sharps were originally designed to be shot with an air space in the chamber. If you get a chance to look, there is no way you can completely fill the chamber and the cavity in breech block and still close the gun.
The last thing I'm doing is having a set of competition sights put on the gun. The original style military sights were pretty hopeless for accuracy and with the new setup, the marginal notch will be replaced by a peep.
Upshot of shooting a Sharps in our competition, it's about the most inherently accurate carbine on the line. The bullet is self centering to the bore, the cart insures uniform bullet seating to the rifling, the cart insures powder is in the same place in the chamber every shot, the breech and barrel are one monolithic assembly with no mechanical flex on ignition. It's not uncommon at all for a Sharps set up this way to shoot 2moa at 100yds with iron sights if the nut behind the stock is worth his percussion caps.