I selfishly spent too much time sharing this not to try for double green stamps from it.
Yeah, I know, a really dated cultural reference.
I have never been a fan of the Italian "floating sleeve" check that due to QC issues often times does not float or work very well. But I understand the production savings which trickles down to cost savings to the customer.
I did not check first, but "they" (Taylor's, Dixie) used to sell the tool that extracts the floating sleeve. IF it is not TOO far "off," it can be deburred, polished, and the chamber polished to enable it to function as well as the thing can function under the design and circumstances. But I would hate to recommend buying the thing and it does not solve the problem. Perhaps, some one you know or someone in your group or circles has one and you could get together.
Anyways, if it does not move or "float" when the pressure in the chamber needs to push it back against the solid breech block face, it will leak. They also leak over time as the sleeve starts to form an impact/wear ring on the breech block face.
Again, the gun is not here for me to examine and see.. but I will venture a guess that you may have a recent enough repro Sharps that it has a Sharps gas check- BUT I am puzzled as I do not recall the Italians making a Sharps gas cheeck breech when they use the floating sleeve check in the chamber? (Because they simplified production by simply casting what would have been the detachable/removeable check plate to be part of the breech block).
But Pedersoli has tried three (four?) versions/variations in the past few years trying to get sometmhing that works and holds up (a larger factor with
N-SSA skirmishers versus reenactors who NUG fire less rounds AND do not generate breech pressures NUG sufficient to get the sleeve to move backwards and tightly butt against the breech block face!))
Original Sharps do have a "sleeved chamber" that was adjustable by an armorer to compensate for the floating breech plate wearing. It was discovered with the pre 1859 tailed cartridge that loose power grains debris worked its way between the gas check plate and the breech block face.
One originals and Shiloh reproductions of originals, the gas seal plate moves forward to seal against the breech by a "pressure differential." At the rear of the gas check plate, an extension fits tightly into a recess made into the block. The extension tapers down towards the rear to somewaht of knife edge. When the round is fired, the gases expand into the recess, applying pressure on the taper. Because the taper is angled slightly , pressure is applied BOTH forward and outward. The breech block moves forward because the recessed area is ever so larger in diameter than the chamber. The pressure from the round is equal in the chamber and breech block area. (The Italian version is straight, it does not taper which reduces its effectiveness.)
But the larger cavity behind the gas plate creates more surface area for the tons or pounds per square inch to push on. There is greater pressure on the back of the gas plate than on the front. As a result, the gas check/seal moves forward.
Also, The "quillotine" or knife edge at the back of the taper also moves to form a tight seal against the sides of the breech block recess, adding to the seal.
Sharps found out that the grit and debris from the powder spilled when the tail of the pre 1859 cartridges got between the block and the gas check/seal plate causing it to become loose. So, just before the War, they redesigned the cartridge to not have a tail and that did not require the breech block top to cut through the cartridge any more.
IF you have a true Sharps type removable plate, there are two recess in its side for a small screw driver to pop it out from its snug fit. If it is the molded solid version there is no plate to pop off/out.
"O" ring modification...
Hmmmm. With the full caveat that I am describing the modifcation perhaps best done by a gunsmith, a machinist, or a lad with machinist skills and tools... and NOT necssarily as a "How To Ruin Your Sharps."
In increasing order of complexity...
1. .875 diameter "O" ring about .125 thick. Square sided are better, round will work. You take out the pressure plate and insert the "O" ring at the bottom of the recess, then put the plate back in. The breech will operate TIGHTLY, but will eventually get loose as the "O" ring gets worn out, and succumbs to the heat and dries out. So, some lads replace them before and after every event.
2. Since the "O" ring takes up space.... some lads mill the back of the recess down a tad- the bottom of the recess needs to be .015 less than the diameter of the "O" Ring and the space between the pressure plate and the breech face. A "feeler gauge' is needed).)
This prevents the really tight working of the loading lever when it closes and compresses down the
new(er) "O" ring.
3. Coin method. I got decent improvement with one of my Sile Sharps by smoothing off a Quarter, drilling a hole in its center for the "flash director" cone in the breechblock, and just friction fit tapping it down to the rear of the recess. That put added space for the floating plate to push back against and eliminated gassing. But it required a machinist making several spare plates as the knife edge had to taken down a few thousands of an inch due to the width of the dime.
4. I won't get into this as it is much more radical. Some lads fit a shaped steel plate over the breech block. Then modify the rear of the chamber to hold two removable, floating ring-like gas checks separated by an "O" ring. When a charge is fired, the gas pressure moving in all directions, pushes back towards the rear. It then pushes the metal double ring/"O" ring sandwich gas seal backwards against the now solid breech block face, making the gas seal. (AS the "O" ring wears out and dries out from use and heat, it too needs replaced.
And as with the Italian floating sleeve check, it does require cosntant cleaning and maintenance.
Sorry, I had a bunch of Sharps images but they are trapped in a dead hard drive, so these will have to do:
Last but not least....
IMHO, Sharps were not designed to fire blanks. By and large, and for the most part, both the originals and the Italian repro's gas checks systems work less-than-best when a bullet is "sealing" the chamber and exerts significant rearwards pressure. Unforuntately not so much with a blank charge's reduced pressures.