Breach threads ?

[jerrywh]

I have seen that rounded thread on some old barrel before. It is not a mistake or an accident. Old barrels made in Belgium had that thread and the plugs to match. I am working on a pistol with that thread now.
 They were done with a tap and die of sort. The only way you can get a plug to match is by making a special thread bit for a lathe. You should be able to cut the top of the thread off of a V thread and it should work.
 I have seen at least a dozen of those.  Dixie sold some about 50 years ago like that made in Belgium. In Europe they used that thread for over a hundred years.  1There is a name for it but I would have to look it up.

[Smoketown]

Many threading dies have a split and a small adjusting screw to allow you to 'fit the threads' to the existing tapped hole.

Cheers,
Smoketown

[Scota4570]

If you ran the bottoming tap in and the plug still won't fit then run a die over the plug. It will fit after that. 

[davec2]

It may be a Whitworth thread......rounded thread form used mostly by the Brits but other countries used a similar form as well.

[Scota4570]

All the more reason to run a die over the plug and a bottoming tap in the barrel.  If if is some odd thread profile that needs to be corrected.    This is a 10 minet job.  I'm not understanding the long debate.   

Bottoming taps can be easily made by grinding the nose off a plug tap.  The die is a common tool.  You need both to install a brech plug. 

[JOHN L. HINNANT]

Good Evening All,

Scota4570 is right about this being a long debate, Scota, you and I MAY have more experience in understanding threads and thread fits, so let us give everybody else the benefit of the doubt.

There are some very good suggestions here, the best one involving chasing the barrel threads and the breech plug threads The adjustable die works very well as has been stated in a previous post.

About regrinding a Plug or Bottoming tap, I have ground a Bottoming Tap as suggested. Been there;Done that. It is best to have two Bottoming Taps and and ground the starting thread and a half off of one of the Bottoming Taps, but be forewarned, the first thread will chip and break very easily thus requiring more re-grinding.

Acquiring all of these taps can become expensive, so just start with an adjustable die and hope that solves the problem. It probably will.

Now..., just in case it is a Whitworth thread, I checked that out. The Whitworth has 55 degree angle threads as opposed to the 60 degree angle thread in our NF and NC . If it has the same TPI as the NF thread, you are home free. The 3/4-16 TPI die can be used to chase over the Whitworth thread.

If I recall my thread history correctly, the USA NC and NF thread were slight modified for machined products exported to England during World War 2. That thread was designated as the Unified NC and NF Thread. With that modification it would interchange with the Whitworth Thread used in England. The Unified Thread was still compatible with the NC and NF thread series.

And by the way, all three of my Bresein barrels have the 3/4" X 16 TPI  thread. That is pretty much the standard for most (not all) calibers over 45.
 

You are definitely right Scota. This turned into a long, long thread about a simple thread. If everybody is not crossed-eye and brain dead from all this by now, (know I just about am) maybe we can get that breech plug thread problem solved now.

But it has been kind of fun......, I think,

My Respects to All,

John L. Hinnant
"God and Texas"

[bob in the woods]

This has been enlightening but I thought it was a simple question, and really was at a loss as to why the plug I purchased just wouldn't fit. Easy for some...frustrating for others.   I'm not a machinist, and usually installing a plug in a barrel is a straight forward job.
I had to purchase the tap, and frankly am at the point where it would have been simpler to just cut the breach off, and redo the thing to fit a normal /standard plug.  Thanks to all for posting.

[TMerkley]

Good Thread,
Keep us in the loop!

[JOHN L. HINNANT]

Good Morning Bob,

Before you have your barrel threads cut off and re-threaded, let us see if that is really necessary. Since you already have a 3/4"-16 tap, did you use it to chase the threads? If so, did it clean up the original threads to any extent?

If you did chase the barrel threads, and they look OK, then I think we can assume the breech plug threads are bit too large in diameter, so having the barrel breech threads cut off and re-threaded is probably not going to solve your problem, just cost you more money. Gunsmiths and machinists are not cheap.

Lets try this first. 

I recently cut the barrel breech threads off a barrel for a friend. He wanted to have an original T-C Renegade breech installed, and it is not a 3/4"-16 TPI. I still have that stubby length of 3/4"-16 TPI threaded breech.

Go to my web site www johnlhinnant.com to get my email address. Send me an email with your USPS address, and I will send you the threaded stub. You can then use that as a gauge to see if your breech plug will screw into it.

If your breech plug will not screw into my cutoff, then I think that we can safely assume the problem is an oversize breech plug thread. If that is the case, I can also help you with that.

In one of your emails you stated that you were not a machinist, so as said earlier I assume you plans are to take your barrel to a gunsmith or machinist to have the the threads in the barrel threads cut off and then re-threaded?. Gunsmith and machinist fees are not cheap, so let us see if we cannot save you some money without having to resort to that with this simple check first.

And besides I do not trust the average gunsmith or machinist to do this job right.

My Respects to All,

John L. Hinnant
"God and Texas"

[Ky-Flinter]

Hi John,

Welcome to ALR.  I know that you know your way around modern barrels, so welcome to the 18th century.   And thank you for embracing the spirit of ALR right from the start.  That's a very generous offer of assistance.  Glad to have you with us.

-Ron

[JOHN L. HINNANT]

Greeting Ky-Flinter,

Thank you for the welcome.

Yes I do know my way around the modern rifles, but what most folk do not know is that my first love has always been the muzzle loading cap lock rifle. I have been shooting them for sixty plus years now. Started when I was 14; am now 77. The Grand Old Man of Texas Muzzle-loaders, the late "Judge" H. E. Resley of Fort Stockton, Texas tutored me on the finer points of building and shooting the ML rifle, starting me on this path when I was 14.

Rifles have always been my focus, having little or no interest in handguns or shotguns. I do not know if my approach to the thread problem is the right avenue, but it is the starting place for my work. I have a strong background as a machinist with a degree in Industrial Manufacturing Technology and a minor in history.

So my approach to this kind of problem is from that background. I have yet to purchase anybody's breech plug that did not require chasing the threads. Others may not have had this problem, but that has not been my experience.

I believe that oversize breech plug threads are the norm in order to make sure they will fit any oversize threads in the barrel breech. A lawyer thing , you know.

My taps for breech threads are special ground to a tighter closer tolerance. Safety has been a super great concern to me. After having the opportunity to "pull" the breech from many originals, it is wonderment to me why the breech plug was not blown out of many of these rifles.

Twenty five years or so back, one of the shooters at the TMLRA Championships showed up with an original rifle with an excellent bore, but a breech plug so loose you could easily unscrew it with a pair of pliers.
The "Judge" using a foot long piece of train rail as an anvil started tapping each barrel flat with a 8-10 ounce ball peen hammer, until he has tightened up the the barrel threads around the breech plug. It worked just fine.

The "Judge"was able to do that because the barrel was made from soft wrought iron. Not sure you could do with one of our modern alloy steel barrels.

Must go for now; have some Pre-Thanksgiving Day chores to do for my wife.

My respects to All,

John L. Hinnant
"God and Texas"

[Topknot]

Mr. Hinnant, I too would like to welcome you to A.L.R. It is so refreshing to have a man of your knowledge on this sight. And one that not only talks the talk ,but walks the walk. What I am trying to say is that you are not only giving advice like most members do, but you are also willing to send part or tools to fellow members to help them out and to keep them from having to buy expensive tools. Its your willingness to help fellow members out at the level that you are doing is what is so refreshing about it. In this day and time it is very rare. May we have more members like you.

                                          Your humble servant,

                                                               topknot