Tapping Barrel For Breech Plug

[zimmerstutzen]

Someone said, let the pros do it. Not a bad thought. However, that isn't what the love of muzzleloading and buckskinning is about. if you are intimidated by the task, sure let a pro do it. I, however, figure the pros learned to do it, they are not rocket scientists, so I figure I can learn to do it. There is some specialized knowledge required, sometimes just learning a few tricks. To learn the proper way to cut threads, I bought two books, Learned about how taps are made, how they work, what lubes to use and when. how to care for them. The sum total of that takes up about 6 pages of a book. First I tapped a hole for a tang bolt to thread into a trigger plate. Since it was at a slight angle, it was actually harder than I thought when I did it, and it worked beautifully. I drill the barrel breech with a brace and bit.

I have a small farm. I can't afford to pay a pro to do every task. you look it up on the net, study it, or find a book and study, then go ahead and do it. Worst that can happen, is that you will have to pay a pro if you failed. I needed a few trenches for water and electric lines. Contractor wanted $4,500. Heck I bought a back hoe for $2700, did it myself, and I still have the backhoe for future jobs and clearing snow from the lane. IMO, a buckskinner celebrates the adventurous independent nature of our ancestors with a "can do" attitude. Not a can't do.

Now, I wouldn't attempt brain surgery, but I give injections, and do minor surgery on animals. Learned to trim hooves and shoe horses. Tune the tractor and adjust the knotters on the baler. I,ve made parts from scratch for machinery. Tapping a barrel breech is a piece of cake by comparison. I have made drums and touch hole liners for guns. Made springs, half soled frizzens, tempered springs, forged trigger guards, and even made a jig for routing barrel channels. carved stocks from tree trunks. Even made and hardened screws and bolts. I may not be a master machinist or "artiste" but I can do a job as good as many so called pros. My daughter was taking shop and was intrigued by sand casting, so we made some sand molds, and melted down aluminum cans on the old brick bbq out back, we used an old vacuum for a blower. Didn't even have to study to do that.

Nope, I think the original poster of this thread was right to ask and right to seek the knowledge. Even more right if he actually does it.

if we let the pros do it, we'd still be protected by Red Coats.

 

[Zoar]

I like the approach of the last two posts.

As I stated, I know how to drill & tap. That was not the original question. I was looking for specifics on tapping a barrel for a breech plug and yes I want to know how it was done with hand tools or older methods. The problem I said was all the books I bought over the internet that had GUN BUILDING in the title were actually about assembling a kit or disassembling an existing gun and fixing it. That does NOT tell squat about tapping a barrel for a breech plug. However with the sage advice given here so far and the one book I have ordered as well as trial an error of parts in my little machine shop, I should be good to tackle this.

Indeed making things is often pretty straight forward, and there are always little tricks or things to look out for---that is what this forum is so good at providing and books on how to do something the OLD WAY.

In a nut shell---the biggest difference between regular tapping and tapping a barrel is to use a bottom tap to eliminate the cone that a regular tap leaves and create a flat-ended thread, in order to get the breech plug to seat utterly flat and flush. That to me is straight forward and I can do that. And of course making everything squared and centered, yet that is true for any precise drilling/tapping work.

I like doing things myself, too. I make pottery from clay on my land and build most of the buildings on my property myself, installed our totally off-the-grid solar system myself, and recently installed two wind mills, I am making my own wind turbine now. And yes having my own little machine shop and various hand tools is very valuable. But I am most interested in starting to MAKE my own flintlocks and wanted to take it one or two challenges deeper into the skill/craft at a time. After building a few kits, I wanted to do more of the "making" and yes using minimal modern tools is the direction I seek. And many on this forum "get it" and being able to converse with a bunch of traditional muzzleloader types is always entertaining and educational! Hopefully I can get some time off from work (self-employed) and attend one of those week long traditional gun building courses and/or blacksmithing.

 

[ehoff]

My only advice is use a three tap set, taper, plug and bottoming. Use tapping fluid and support the tap with a tap center. When using the plug and bottoming taps make sure to remove the tap and clear out the chips often, especially when your near the shoulder. You might think its hard to snap a big large tap like 5/8-18 but it can happen quick. Also when you near the shoulder the you have to take care so that the front face of the taps don't cut into the shoulder.

If it was me I'd set the barrel up in a 4 jaw chuck on a lathe, bore the hole and then chase the threads using an single point threading tool on a boring bar.

 

[zimmerstutzen]

and the absolute best taps you can buy. None of those black things from the bargain bin at Walmart.

Have you checked Chuck Dixon's book about gun building? I haven't looked at it in ages, but I seem to recall that his book is where I learned how the breech plug face andd base are supposed to match up with the barrel breech and inside edge as well. A good square and a sharp file are essential if you don't have a lathe.

 

[Zoar]

I will look for it.

 

[bob243]

I noticed on a lot of barrels that are threaded from the factory there is about a half turn where the bottoming tap bottoms out and there is no thread.. What does everyone here do to over come that and get the plug fitted properly into the shoulder?

 

[bioprof]

In one of the books that I have read, they ground off the threads for about the first 1-1 1/2" of the tap and left the end the same diameter with the bore so as to act as a pilot. This keeps the tap centered with the bore so it doesn't get off to one side. It's kind of the same concept as a coning tool, except instead of crowning the muzzle, you use it to thread the breech.

 

[Melton Kidd]

I use a bottoming tap from TOTW THAT HAS A 1/2 thread clearance and run the barrel makers threads with that. Then very slowly fit the plug by chamfering the end. Use carbon black or lipstick or other color transfer to determine when you have a good fit. If the plug is to short, you have to remove metal from the breech end of the barrel and fit as stated above. TOTW catalog has a paragraph about the measurement of flats ( how much to take off for 1/2 flat etc). Some barrel makers mark the bottom flat and everything has to match that. Some makers have all flats the same so the breech plug can line up with ant flat

 

[bob243]

Ok, I was wondering if I was doing the correct thing. I have been chamfering the end of the plug about half a turn worth of thread. I do get good contact on the shoulder of the bore as well. (I just use a red marker) Thanks

 

[Zonie]

I noticed on a lot of barrels that are threaded from the factory there is about a half turn where the bottoming tap bottoms out and there is no thread.. What does everyone here do to over come that and get the plug fitted properly into the shoulder?

The barrels that do not have threads running clear to the bottom of the hole do not present any real problems.

The length of modern breech plug threads is a little greater than it really needs to be for strength so use your fine tooth flat file and file off the first 1 1/2 or 2 threads.

This can be done easily by putting some masking tape on the threads you want to keep. Then lay the threaded area into a vise with the jaws opened to about 3/8 of an inch for support.
File some of the exposed threads off and rotate the plug slightly and file again.
Repeat this rotating and filing.

By taking your time you can remove the two exposed threads right down to the bottom of them and because the front threads are now gone they cannot interfere with the unthreaded area in the barrel.

The lack of these 1 1/2 or 2 threads is not a safety issue so shooting the gun will be totally safe.

 

[J.D.]

IMHO, if drilling by hand, or even by machine, grind the point of the drill bit flat. Run the flat point drill into the drilled hole to cut the bottom of the hole flat.

Tap as described. I much prefer threads as close to the bottom of the hole, as possible.

The coupla Rice barrels have seen have roughly 1/4 of one thread champhered to allow the face of the plug to bottom out on the bottom of the hole.

IMHO, Rice fits 'em better than the other barrel makers I have seen. Getz does pretty good too, but turns a coupla threads off of the front of his plugs to get a tight fit. IMHO, I prefer the fit of Rice's breech, but Getz's fit works ok too.

The 18th century smiths used a cutter, with cutting teeth on one end, similar to the end of an end mill, usually used in conjunction with a pilot in the bore, to cut the hole for the plug.

Taps and screw plates were often home made, but commercially made tools were offered by retail shops.

I have never heard of a breech plug welded to the barrel in the 18th or 19th centuries. Never!!

If anyone has documentation to suggest that welding breech plugs to barrels was done, written by someone who knows what they were seeing, I will gladly look at it.

God bless

 

[zimmerstutzen]

I have seen two instances of the breech being forge welded at the same time as the barrel was welded from a flat piece wrapped around a mandrel. In fact, the Fox Fire books show such a thing in one of the early books about old style Mountaineer gunsmiths. I personally would never trust such a thing. In every old gun I have, I can see where a breech plug was a separate piece of metal. Every except one. In that one, I really can't tell at all, and that gun is the oldest, probably early 18th or late 17th century. I even have a gun in which the breech plug has female threads and the male threads on the barrel screw into the breech plug. (or more correctly, breech cap?)

In the very early days, when gun barrels were crudely banged out by hand I suspect that it was easier to forge the breech as an integral part of the barrel.

The two I saw were smooth bores of small caliber. No need for running a rifling machine cutter through.

 

[Zoar]

All---

Very good discussion and information. This is very helpful.

Now, I do have another question---50 caliber (.500) barrels call for a 5/8 Breech Plug usually 18 threads per inch. I bought one from TOW and it arrived Saturday. I also ordered two taps---a standard 5/8 inch 18 and a BOTTOM tap in 5/8 inch 18. However, a 5/8 inch tap calls for a 37/64" drill bit (Ergo a 37/64" hole).

Now, my barrel is end to end .500 rifled bore. So I assume I need to open up the breech end a tad with a 37/64" drill bit before I use the first 5/8" 18 standard tap. And I just drill to the depth that equals the length of the breech plug that will reside in the barrel.

Yes?

 

[zimmerstutzen]

Measure the distance from the plug face to the rear surface that meets the barrel, carefully, and meaure that distance from the corner of the shoulder of the drill, minus about two millimeters and wrap the drill with tape as a depth guide.

I've used a standard brace to drill the barrel which was held in two lead blocks in a big bench vise, that was bolted to a big heavy work bench. Actually clamping it in securely without squeezing or marring it is the tricky part. Large wooden block can be used.

Drill to just shy of the depth you need annd then measure with a vernier and compare to the breecch plug. keep in mind that the drill face will leave a 60 degree angled step and you will have to either find a way to cut it square or chamfer the breech plug face to a similar angle as the drill point. Once you are close, it becomes a matter of trying it, with carbon black or lip stick to see how well the inner face matches that shoulder and how close the outer edges are matching up.

You can always remove more, it is darn hard to put some back, so go slow.

 

[Zoar]

So just to be sure, I am asking the following--- QUOTE FROM ABOVE POST---"Now, my barrel is end to end .500 rifled bore. So I assume I need to open up the breech end a tad with a 37/64" drill bit before I use the first 5/8" 18 standard tap." Is that true?

Yes? or No?

 

[zimmerstutzen]

You want to open the bore up to the diameter of valleys of the thread on the tap. They will be the peaks of the thread left in the barrel breech.Since you want to most crisp peak possible in the barrel breech, you need to leave that amount of material. If you take more than that, you end up with peaks with the tops leveled off. (They end up looking more like an Acme thread if you take too much.)

37/64 may not be exact, but it is certainly where it should be according to most tables for tapping 5/8 inch Nat fine threads. If you were tapping Nat coarse, I believe you would need to leave even more material

 

[Vaino]

YES.... my tap drill chart shows that a 37/64" drill yields 62% thread depth while a 9/16" drill yields an 80% thread depth which is better for breech threads if the plug fits....Fred

 

[Zonie]

If it were me, I would go with the 37/64 tap drill for the 5/8-18UNF thread.

This size is in the range of the minor diameter for the .625-18 UNJF high strength threads used on aircraft and other applications where a high strength fastener and thread series is required.

That said, IMO, the strength of the breech threads for a black powder muzzleloader application should not need to have a greater percentage of female threads.

 

[bingo1952]

That will give approximately 80% thread engagement. Also allow at least 5/8" of engagement for maximum strength. Any more than that is redundant. JMO HTH

 

[Vaino]

Judging from the thread fit on Rice bbls, it seems they have more than 60% thread depth. When screwing in the breechplug, resistance can be felt long before the plug bottoms out. Would be interesting to find out what they shoot for.....Fred