Vent hole position in chambered breech

[smart dog]

Hi Folks,
My tool and die making neighbor machined a chambered breech for me for a late English flint gun.  He made it from 4140 steel, with a 0.375" diameter powder chamber that is 0.97" deep and radiused at the bottom. The lip of the chamber is also chamfered and rounded. Where is the best location for the vent hole.  I plan on using a white lightning coned liner.  Should the hole be right at the very bottom of the chamber or up one side a tiny bit?  Or does it matter? This is not a Nock's breech, just a simple powder chamber.

dave   

[smylee grouch]

I have done about 12-15 of the Nock style and try to get the edge of the cone to be at the bottom of the chamber to help with water flow. Will your vent go through the threaded portion of the plug?

[smart dog]

Hi Smylee,
No.  The vent goes into an octagon section, which is about 1" long not the threaded plug.

dave

[bgf]

Smart dog,

My 1 1/8" chunk barrel  touch holes are centered ~7/16 forward of the exterior rear of the hooked, chambered breech, very similar in dimensions to yours.  Not saying it is right, but with the standing breech, that puts the touch hole (and lock) roughly where it would be with a standard breech, and I've had no issues with ignition or fouling.  If I remember correctly, the placement was 2/16" forward of the inner depth at center plus 3/16" so a 3/8" hole would fit (actually used 1/4) without touching the radiused section at bottom.  I think I was aiming for the shortest powder passage, though I doubt placing it further back if desired would cause problems...

Hope that helps more than hurts!

[smart dog]

Hi Folks,
Thanks for your input and help.  I decided to drill the hole such that the back edge of the cone on the liner is flush with the radiused bottom of the powder chamber.  After drilling and tapping the hole, I had to grind the bottom of the powder chamber smooth again because the tip of the drill and some threads entered the chamber.  The result is that the actual hole is half the radius of the liner cone forward of the bottom of the chamber and the passage from chamber to liner is smooth and polished.  I did pretty much what Smylee described and what I noticed in various diagrams I have of chambered breeches.  Thanks again.

dave

[bgf]

Thanks for the follow-up.  Your placement should be fine and Smylee had a good reason for it.  It should be great aesthetically as well, being as far back as a standard breech with a short breech plug.

My case was probably a little different due to thickness of the barrels: Even in the non radiused section, a full length liner seats without threads going into the powder chamber!  I suspect functionally the placement is fairly non critical and up to the builder's goals.

Looking forward to seeing the result.

[Blacksmoke]

Dave: I agree with "smylee" the vent should be as close to the back of the breech cavity as you can get it.  This will make the  ignition of powder more efficient and a more consistent burn than a vent being slightly ahead of face of the breech plug.  I do all of my breeches in this manner.  It also means that you are now able to get the lock fence back against the recoil shoulder where it should be!  Just because some old originals did not have this feature doesn't mean that you can't.  Just saying,   Hugh Toenjes