homemade barrel breech plug

[tat]

I have a "beater" 17" .50cal octagon barrel that I need to plug. I am thinking of making a 14" pistol out of it but the stock design I am planning I need the back of the barrel to be flush.

Is it safe to drill and tap the back and modify and slot a grade 8 bolt to screw into the back for a plug?

If so should I use course or fine threads and how deep should I go into the barrel?

I plan on building/welding the lock mech. onto the bottom of the barrel and "hiding" it in the stock.

I appreciate any suggestions.

Tommy

 

[Zonie]

I'm not sure I can visualize exactly what your proposing, but a grade 8 bolt is probably a case of overkill (not that that is bad).
Most .50 caliber barrels use a 5/8-18 (fine pitch) thread and the depth of engagement is about 9/16 to 5/8 of an inch.

The reason for using the 5/8 thread is it assures a shoulder where the bore ends and the threads start. This shoulder or face is what the plug seats against, forming a gas tight seal.

If you used a 9/16-18 thread, the tap drill would be a .516. This in a .50 caliber bore would leave no shoulder for the end of the plug to seal against.
Because these are standard threads, not pipe threads, they will leak gas between the major diameter of the plug and the major diameter of the female threads in the barrel.
Although this could be "sealed" with some of the thread locking compounds or teflon tape, it is not the best way to do it.

Hope this helps you.

 

[tat]

Zonie,

Thanks for your reply!

I should have been more clear, the barrel I have is a blank. It is not threaded or anything, it is chopped off and the inside is rifling. I was thinking of drilling it out to maybe 3/4" diameter and tapping it around 1/2" deep and plugging it so the back of the barrel would be plugged and be squared off in the back.

I hope this makes sense

Thanks again!

Tommy

 

[Zonie]

It does, and as I indicated, you could use a 5/8 dia bolt.

One thing to consider is how you are going to keep the back of the barrel down in the stock. That is why most of these guns have a tang sticking out the back of the breech plug. It serves as a good handle to drive a screw thru to keep the breech of the barrel from trying to kick up out of the wood when the gun is fired.

As I mentioned, the grade 8 bolt (high strength steel) is a case of overkill and the weak place in the joint will be the barrel. Usually the barrels are made of low carbon steel with fairly low yield and tensile strengths.

The 1/2 inch you are proposing is probably ok, but I wouldn't use less than that because of the strength of the barrel material.

Happy building.

 

[tat]

Thanks Zonie!

I will use a 5/8" and I will go 3/4" deep into it for good measure. :thumbsup:

I can weld some lugs on the bottom of the barrel to mount it in the stock.

I appreciate all suggestions!

Tommy

 

[Old Salt]

Tat,

I will use a 5/8" and I will go 3/4" deep into it for good measure.

Keep in mind the location of the touch hole (if flint) or the flash channel (if percussion). If the breech plug is too deep you might have to (a) move the barrel to the rear or (b) drill your flash channel into the breech plug to get things to work out.

I'm new to building ML's but I'm pretty sure that some care needs to be taken in that area.

Old Salt

 

[tat]

I am glad you mentioned that!

What is considered a good safe depth for my application?



Tommy

 

[Old Salt]

Tat,

What is considered a good safe depth for my application?

Some one of the guys with plenty of experience should answer. Zonie, Birddog, Rich Pierce, StaticX, I'm already over my head.

Old Salt

 

[davy]

Tat,

What is considered a good safe depth for my application?

Some one of the guys with plenty of experience should answer. Zonie, Birddog, Rich Pierce, StaticX, I'm already over my head.

Old Salt

I dunno ... but when I was researchin the same thing somewhere I came up with the depth size of 1/2 inch but 5/8 would be better .. both with a fine thread! If you can believe it, my Pedersoli Frontier flinter has a "1 and 1/4" inch length breech plug! Talk about overkill! :shocking: And yes the touch hole is drilled thru the breechplug! :curse:

Davy

 

[tat]

Thanks for your replies!

Zoni mentioned using some type of thread locker or teflon tape on the threads. There are two types of loctite the kind you need a torch to get off and the lesser. The torch type sounds good but I think a torch would discolor my metal finish if I ever needed to remove it. What do yall think?

Also the lock system that I am having to make so I can hide it within the stock may require me to screw the nipple directly to the barrel. Is this a problem?

I dont think I can drill the nipple thread tap hole all the way thru, can I? I am thinking I will drill the diameter of a touch hole all the way thru and then drill the nipple thread hole just deep enough to fully seat the nipple after threading. Am I on the right track on this?

Also what is the diameter of an average touch hole?

Tommy

 

[Zonie]

If your plug is 5/8 or 3/4 long, and the 1/4-28 nipple hole was about 5/16 deep, your "touch hole" would be about5/16 to 7/16 long. If the size of this hole were similar to a flintlocks touch hole, I feel it would be much too small and too long for reliable ignition.

As the standard design for a nipple hole can allow the nipple to be in communication with the bore with a relatively large hole (bigger than 1/8 dia) without suffering problems, I would think that running the minor diameter (tap drill) thru to the bore would not be a problem.
In fact, because having the powder from the powder charge right up against the bottom of the nipple gives the fastest most reliable ignition, I would say forget the "touch hole" idea and run the tap drill on thru the plug. It won't weaken it enough to talk about.
Actually your chief problem will be drilling and tapping the bolt if you use a grade 8. It gets it's strength from being fully heat treated and will be tougher than owl doo.

 

[tat]

Zonie,

I Wonder what would happen if I put the nipple/touch hole arrangement just in front of the plug coming into the "bottom" of the barrel. This way I would not have to go thru the plug, but only the barrel.

Going thru the bottom will give me the opportunity to still hide the "lock" in a slot in the stock.



Tommy

 

[Old Salt]

Davy,

If you can believe it, my Pedersoli Frontier flinter has a "1 and 1/4" inch length breech plug!

Doesn't the Pedersoli used a patent breech. I believe it is normal for the touch hole to be drilled into the breech plug on a patent breech. Then another larger hole is drilled from the face of the plug to the touch hole. On my GPR the second hole diameter is about .357".

Tat,

Some pretty reliable sources have told me that a flintlock touch hole is best located from the face of the breech plug to about 3/32" in front of the face, depending on the thickness of the liner you use and if you use one. Once again, others have more experience than I.

Old Salt

 

[davy]

Here is a picture of the tang area of my 45 cal Ped Frontier I posted a while back ... note the position of the touch hole in regard to the breechplug length and face .. I wish I had thought to photo the breech plug while I had it out .. but .. I did not .. you can see the general outline of what it looks like in the picture ..

Davy

 

[Zonie]

Zonie,

I Wonder what would happen if I put the nipple/touch hole arrangement just in front of the plug coming into the "bottom" of the barrel. This way I would not have to go thru the plug, but only the barrel.

Going thru the bottom will give me the opportunity to still hide the "lock" in a slot in the stock.



Tommy

Installing the nipple directly into the wall of the barrel is the much prefered way. As I said, I don't know exactly what your building so I'm trying to read between the lines.
Installing the nipple directly into the wall of the barrel is the method used on "underhammer" and on "mule ear" guns.
These guns are noted for their instant ignition. ::

 

[Old Salt]

Davy,

Sorry to take so long to get back to you. I was away for a few days. That is a patent breech, the same as Lyman, or T/C except the dimensions probably vary. I've seen one of Lyman patent breeches off the barrel.

Most of the parts sets or custom rifles available on the market today do not use the patent breech. The face of the breech is flat and the touch hole comes through the barrel just in front of the face of the plug. Somebody correct me if I'm wrong but I think most of the breech plugs are 1/2" to 5/8" deep. It is important to know and to plan for that dimension.

How did it effect the ignition when you bored out the powder chamber in the breech plug?

Old Salt

 

[davy]

Well just so happens I went out with it and have shot it a couple of different days now since John Hinnant bored and opened up the chamber ... no misfires to date to speek of that I cannot attribute to my own poor habits of keepin the touchhole clear and pan clean etc ... so I am guessing it solved a problem for me no doubt! I am certainly having less problems with it, and so much happier ta boot! :g

Davy