Breech plugs and force

[jerrywh]

 Note on the arrows on the illustration below.  The force on a breech plug is about 1/4 the force on the barrel walls because of the difference in the area. Also note that it is not seated in the way some profess it be done today.  There are three or four different ways to seat a breech plug and in my opinion they are all good, safe and sufficient.  The French had their way. The English had about three or four ways and we have our ways. Manton had one that screwed over the outside of the barrel. A good question to ask oneself about a plug is this. What will move first the bullet or the breech plug or the Barrel wall?  The last thing to move would be the plug if it is tight.


 

[webradbury]

Jerry, do you have any illustrations of the ways to seal that you mention. I hopefully will be able to work on mine tomorrow and maybe finish the plugs.

[Scota4570]

Interesting illustration.

I don't see how it could be made.  First the plug thread is exactly what would happen if the hole for the tap were bore diameter.  In order to give the chip at the nose of the bottoming  tap a way to break off you need a relief groove.  Then you have a shoulder to seal against........

Second, the all thread between the plugs?  It would be impossible to assemble the plugs to the barrels.  To make it "assemble-able" the piece of all thread has to be smaller than the ID of the vent liner threads.

 And then it would need to be tapped after the plugs were installed so one could screw it in the holes.  What purpose does it serve anyway?  The plugs are keyed one inside the other.  The barrels are soldered together.  It serves no purpose I can see. 

Could this diagram have been made deliberately  misleading to protect trade secrets?

[webradbury]

I say, good chap...those fellows back then were absolute geniuses! It's extraordinary what was accomplished all without the luxury of power tools or CNC machines! Jolly good show! (Trying to use my best english accent)

[Elnathan]

Second, the all thread between the plugs?  It would be impossible to assemble the plugs to the barrels.  To make it "assemble-able" the piece of all thread has to be smaller than the ID of the vent liner threads.

 And then it would need to be tapped after the plugs were installed so one could screw it in the holes.  What purpose does it serve anyway?  The plugs are keyed one inside the other.  The barrels are soldered together.  It serves no purpose I can see. 

I suspect that they were made with two separate screws, one per breech, not a single screw attached to both breeches.

These things were forged and machined without the benefit of modern drill bits.  Could the use of a hole drilled all the way through the breech and closed with a screw be related to the use of a reamer to open a hole punched while forging or drilled with a period bit?

[jerrywh]

I'm sure this is not a precise drawing but is intended to illustrate the setup. The screw in the middle is actually two screws. As far as the plug screw goes they has special tools to thread the breeches and they did have drill presses. I once saw a early drill press it was a horizontal one made of hard wood. Manton had over two hundred employees at least a dozen lathes in his shop. Nock's breech came into play around 1815 I would say. They made very sophisticated chronometers and Clocks. This machine job was simple for them. I have a photo of a Joseph Manton Clock that will blow you mind.

[L. Akers]

Nock's breech came into play around 1815 I would say.

Nock's breech patent was 1785.  Manton's design was a work-around the Nock patent.

[Goo]

If this is an illustration of a double barrel I don't see the center rib illustrated between the barrels ?

[frogwalking]

The section shown is taken longitudinally along the barrel axis at the centerline.  the ribs are not involved in this location.

[D. Taylor Sapergia]

I have a pair of flint 15 bore Staudenhauer barrels, and they are breeched very similarly to Nock's patent illustrated here.  The thread journals are only 3/8" long, and the OD of the journals is just over bore diameter, just as shown in this drawing.  My barrels were used hard, well into the percussion era, as the vents had been drilled out for drums and nipples.  Yet, when I took out the breeches, you can still see the case hardening colours.  There was no gas cutting or leakage whatsoever.  The journals simply end...no shoulder.

[jerrywh]

 I have never taken a breech plug out of an antique gun that was seated on a shoulder in the bore. However I still think it is a good idea. That usually can't be done on a shotgun because the barrel walls are too thin. Also Most of them were pretty short. I have a few of them in the shop someplace.

[Daryl]

The breech of my single barrel cap-lock Blissett is as Taylor described - but with 1/2" of threads. The end of the plug ends just as Jerry shows in the picture of the SXS, with an angled ramp into the cup of the  patent breech.

[Dphariss]

Interesting illustration.

I don't see how it could be made.  First the plug thread is exactly what would happen if the hole for the tap were bore diameter.  In order to give the chip at the nose of the bottoming  tap a way to break off you need a relief groove.  Then you have a shoulder to seal against........

Second, the all thread between the plugs?  It would be impossible to assemble the plugs to the barrels.  To make it "assemble-able" the piece of all thread has to be smaller than the ID of the vent liner threads.

 And then it would need to be tapped after the plugs were installed so one could screw it in the holes.  What purpose does it serve anyway?  The plugs are keyed one inside the other.  The barrels are soldered together.  It serves no purpose I can see. 

Could this diagram have been made deliberately  misleading to protect trade secrets?

It was made by the British. AND you have to understand that the threads were not made with mass produced "tolerances" (slop) built in.  The threaded plug BETWEEN the powder chambers was there to CREATE the chambers and to FORM the gold or platinum vent liners. Which were, if I am correctly informed peaned into the threaded steel/iron liners to prevent erosion then drilled. This required a punch on the back side to form the softer metal.  The way the liners were is not actually shown here.  I suspect that the threaded plug was not one single plug but was a separate plug for each breech. The way the breeches were fitted to each other is not shown here either to allow them to be installed/removed.
The problem WE have today is that we are using standard modern threads with the built in slop between taps and dies or factory threaded parts you BETTER have at least SOME shoulder or the threads for 3-4 back will have powder fouling in them. THEY LEAK. They will, for example leak oil if not plugged with fouling. We have to remember that MODERN threads and GUNSMITH tools of the 18th 19th C are not the same thing.
The Nock breech was really the first patent breech. It was very consistent in its ignition times according Larry Pletcher. I made a Nock form breech for him to test and this is what he found. Not the flat out fastest but fast and VERY consistent. So for WING shooter its the best choice.  HOWEVER, the one on my 16 bore rifle will not tolerate crappy powder. If the powder burns such as the create flakes of fouling the the bore and one falls over the small (.200" in my breech IIRC) passage it will not allow powder into the chamber and the charge will not fire. Which tells me tha British may have had better powder than we think by 1785. 

Dan

[Dphariss]

Check out the tensile numbers for a threaded bolt. Then calculate the breech thrust on the face of a breech calculated in Square inches. Using any possible BP pressure (with long bullets, 3 calibers long, and large charges of powder this will top out at about 30K). Shotguns produce far less pressure then this. Formlua for the area of a circle is 3.1415 x (circle's radius squared). For a 58 cal this would be 3.1415 X  .0729 if my math is right so the exposed breech face in a shouldered 54 rifle (with the groove diameter as the max diameter of the bore I used .27 for a radius). It come out to a little over 1/4 square inch.
The square inches is pretty small even at 30K psi a 3/4" breech is not going to blow out unless the BARREL fails in some way. At the typical RB rifle pressure level there is a considerable safety factor if the threads are the same length as the threaded length of a nut for the same bolt size.
http://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm
Dan

[jerrywh]

Dphariss
   You are the first person I ever heard who knew how the gold vent liners were installed on the British guns back then.  I have known but never told anybody.  Now the secret is out. They should be small on the inside and large on the outside.

[Dphariss]

Dphariss
   You are the first person I ever heard who knew how the gold vent liners were installed on the British guns back then.  I have known but never told anybody.  Now the secret is out. They should be small on the inside and large on the outside.

Don't know where I picked this up. But when I read it the idea clicked.

Dan

[Turtle]

Concerning leakage past the threads; I put anaerobic sealer such as low strength(blue)  locktite on the threads, and careful examination of the threads when several barrels were disassembled after years of use  showed no leakage. The plug also comes out easily.
                                                                       Turtle