Double shotgun breech plugs causing me to go bald (and it will be a short trip)

[webradbury]

I have turned no less than five plugs for a set of 16 gauge barrels and cannot seem to get them to fully seal at the forcing cone.  After reading Runastav's build last year, i was all excited and he made it look easy.  I believe it would go very quickly if I could get the plugs to fit correctly.  I couldn't fit the barrels in my lathe the way Runstav did so I threaded them by hand, following W. Brockway's book.  I almost want to cut a small shoulder at the beginning of the forcing cone for the plug to seal against, however this will thin the barrel there and if you ask me, shotgun tubes are already thin enough.  Brockway just says to thread the chambers and the plug will stop and seal at the forcing cone.  The problem is getting the fit just right with file work (basically hand fitting).  I looked at my taps last night and the bottoming tap isn't quite as "bottoming" as it needs to be.  I have another that I will use and I am thinking about removing about 1/8" from the bottom of it to remove the tiny bit of taper that is present.  Since the threading is already present in the chamber, it wont be an issue to start a tap with no taper and it will cut more at the bottom of the threads next to the forcing cone. 

If this doesn't work, I hate to be a quitter, but I'll probably use my two locks and stock blank for something else.  I will be out of a nice set of barrels (which stings).

Sorry for the venting

[Ky-Flinter]

..... I am thinking about removing about 1/8" from the bottom of it to remove the tiny bit of taper that is present.  Since the threading is already present in the chamber, it wont be an issue to start a tap with no taper and it will cut more at the bottom of the threads next to the forcing cone. 

I have several taps done that way for cleaning up that last little bit when hand fitting a plug.  You have to be careful though, the leading cutting edge is fragile.

[Scota4570]

I have found the moly paste allows more toque to be applied without fear of galling the threads and sticking the plug.  IF you are super close this may help.  I use the moly bore prep paste.  IT may not be good for the intended purpose but it is very helpful for fitting breech plugs.

I made one double.    I recall putting dye chem on the plug snout.  I ran it in.  Where the blue was gone I filed that spot with the plug chucked in the lathe.  Cold blue is very good for this too. 

[jerrywh]

The main difference between the best in the world and the average craftsman is the best never quit until they achieve their goal. Never quit.
  I have made a lot of taps as you described. Do whatever it takes to accomplish the task at hand.  Did you make a cerrosafe cast of the chambers before you started. I'll bet not.  Do not be in a hurry. There is more than one way to do this. I am going to a shoot so cannot explain now but might be able to tell you later. I will have to do some drawings.
 It might help if you put the barrels aside and work on another part for a few day while you think.  Thinking usually accomplishes more than working.

[runastav]

Hi Webradbury.
I think it is not critikal to use a good bottom tap, see the breachplug is very long with plenty treads. Mine is very thin in this era, but it withstand a heavy prooftest :)So grind the breachplug taper in front, hope you dont give it up!
Runar

[webradbury]

I have been using Prussian blue while fitting. The first plugs were nice but I messed up removing too much material to make the hook at the back this not leaving enough behind the chamber. The next set were nice but too loose. I then used an adjustable die to make them a little tighter and now they won't touch the forcing cone all the way around. I guess I'll keep tryin since jerrywh just called me out on it, LOL!

[jerrywh]

 I'm not sure I completely understand the problem. In the case of the first set, if there wasn't enough metal left behind the plugs for the hook you could thread a piece on the back of them for the hook. If I were doing this I would thread the barrels on a lathe or use a tap with a long pilot on the end to fit the bore. If the taped holes are not straight it will be near impossible to get a set to fit the forcing cones exactly. I made my own taps for that purpose and the threads are 20tpi. One way to do this is to sleeve the forcing cones first. Then make the plugs to fit the back of the sleeves. The sleeves can have a flat shoulder to butt against  the plugs. Put the sleeves in with sleeve locker.

[Goo]

Why can't you use a crush washer or crush seal ?    Soft forming steel ?

[Long John]

W.E.

It seems to me that facing the plugs with a real soft, plastic metal might be the answer.  If you tinned the fronts of your breech-plugs with a nice thick layer of soft tin/silver solder you might be able to get the solder to deform and fill-in the gaps as you threaded the plugs in the last few degrees to form a good seal. 

On the barrels for my double gun, Robert Hoyt made conventional breech-plugs that have a bit of a shoulder.  I was able to get a nice sealing fit.  Of course, soldering the barrels together, making filler strips, soldering all the giblets onto the filler strips and then soldering all that together is a "job".  I'm only 1/2 way through it, so I guess using a retired set of barrels has its advantages.

Best Regards,

John Cholin

[webradbury]

I think I figured out what to do.  I reamed a small shoulder at the beginning of the forcing cone that the plug will seat against.  I think think this will solve the issue.  I also modified the bottom tap to cut the threads closer to the forcing cone instead of tapering out, should be stronger as I'm gaining that much distance in more thread surface.  I will turn some new plugs tomorrow and let you all know how it goes.  Will

[jerrywh]

How far up the bore did you thread?

[webradbury]

From the breech, the threads stop before the forcing cone. All in the chamber.