Sharps O-ring modification question

[Terry Schultz, 10057]

I have an IAB Sharps carbine that has been used for reenacting for many years. It belongs to my reenacting group and is our loaner gun for new members that have not yet been equipped. The last time is was use is before Covid and my Captain brought it to me a several months ago because the last person to use it did not clean it and the block was frozen in the receiver. I tried Krol oil for a couple of months but could not get it to budge. Then I tried a new product I saw on TV called Superzilla and in 2 days of soaking it I was able to get the breach block out. Once I got it cleaned up and all the old powder & rust removed, I noticed that when I re-inserted the block into the receiver the plate on the block was loose. I took it out to the range and tried about 7 paper blanks with it using some CCI reenactor caps. It fired most of the time but there was a lot of exhaust coming out of the top of the receiver where the plate on the block was. I was remembering that long ago I had heard of installing an O-ring between the plate and the block. Can anyone please tell be what size and material the O-ring is? I did a search here but could not find anything about it.

[Jim_Burgess_2078V]

A rubber O-ring job may help create a better gas seal on the IAB Sharps as long as the face of the gas plate and opposing chamber sleeve show little corrosion. Your test with blank ammo very likely did not generate sufficient pressure to function the gas plate on the breechblock and create a tight seal. Before getting an O-ring job, you might want to shoot it with a standard target load. Just keep your hands away from the breech just in case it still leaks gas.

Jim Burgess, 15th CVI

[Terry Schultz, 10057]

Jim
you are correct blanks do not provide enough back pressure to fully operate the gas seal system. But I have been using Sharps and other black powder guns for Civil War reenacting for many years and for the most part they only produce small amounts of leakage from the breach with blanks. This particular gun was miss-treated and the block (not the plate that moves) is heavily pitted and there is a good size gap between them. I tried getting some O-rings from my local hardware store but I was unable to get one thin enough to allow the breach block to be installed in the frame. I have some very thin & soft O-rings on order and I hope that by using one between the block and the plate I can reduce the leakage. I drought that this gun could fire a live charge with any accuracy as the barrel is also in rough shape because of neglect. The O-rings should be here tomorrow and if I get some time, I will try one and see what happens.

[Maillemaker]

You could put a ball of clay where the o-ring would go, and put the gas check plate in place and remove it, and then measure how thick the clay is.

This will give you a compressed o-ring thickness. O-ring should be compressed like 20% I think, for a static seal.

Steve

[Terry Schultz, 10057]

I was able to find an O-ring that was thin enough to use in the gun. I got it from McMaster-Carr, it is 1mm thick with a 20 mm I.D. It also says it is a BN50 which I think is the softness of the material. It is a tight fit to get the block back into the frame but it eliminates the space between the plate and the face of the receiver.

[Jim Brady Knap's Battery]

Back in my helicopter maintenance days I had access to laminated shim stock. It came with 2 thousandths inch laminations. It was simple to measure it out and peel off what you needed. Used a large hole punch to make the hole for to fit the check plate collar and cut the outside to shape of the plate itself. Worked great and lasted a very long time. If you needed to face off the plate at some point you could add another lamination or so of the shim stock. This looks like what we had. laminated stainless steel shim stock | McMaster-Carr (https://www.mcmaster.com/products/laminated-stainless-steel-shim-stock/)

[Terry Schultz, 10057]

Jim, Thanks I will look into it.

[Maillemaker]

You can rebuild civilization with McMaster-Carr. :)