That Pesky Breach Plug

[mogrene]

So I'm now on my second breach plug and I think I figured out the problem I had with the first.

It appears that the threads in breach chamber of the barrel do not extend all the way from the breach end of the barrel to the bore shoulder. This is what screwed me up the first time; I thought I was against the shoulder when I wasn't.

In "Gunsmith of Grenville County," Alexander says to check for this by examining the plug thread. Sure enough, after I installed and removed the plug, there was a small burr in the thread near the face of the plug that I hadn't noticed earlier. He recommends filing down this burr. By continuously installing and removing the plug and removing the recurring burr, eventually the plug face will move past the threaded area will sit snug against the shoulder.

Alternatively, I could retap the breach with a 5/8-18 tap, cutting the threads all the way to the shoulder.

So, two questions:

Which approach do you guys suggest?

If I retap, do any of you know if the Colerain barrel and plug are cut to national fine (NF) or national course (NC)? Is there a special tap used for this or can I pick one up at the hardware store?

By the way, this may explain the 1/16" gap in prebreached Colerain barrels that JD and Birddog mentioned in earlier posts. If ending the threads short of the bore is a normal feature of Colerain barrels, and if the person doing the breaching is not aware of it, you will always have the face of the plug stop short of the bore shoulder.

Is this common with other barrels? I don't remember it being a problem with the Douglas barrel I used on my earlier gun.

 

[mikemeteor]

another, perhaps easier alternatve folks often use is to remove (with a small file) all or some of last course of thread from the plug itself - then there's no plug thread to run up against the shorted barrel thread.
File it down to the minor diameter.
This is more efficient than taking it off burr by burr as you suggest Alexander recommends.
Otherwise, you have to buy a bottoming tap and even then perhaps still grind some off the business end without losing temper.

 

[jdkerstetter]

Do Like Mike just said. It is common to have to rebate or taper the last couple/few threads on a plug. Pulling more than a few factory installed plugs has revealed this. Some have up to and 1/8" of the end of the plug turned down.

You will still have a good fit at the breech as long as you ensure you do not make the plug face a smaller diameter than the bore...and that shouldn't be a problem. Remember, the threads don't make the seal, the face of the plug snugged up against the shoulder does, and you will have adequate threads to hold it up against there.

Enjoy and Good Luck, J.D.

 

[ohio ramrod]

To tap the threads all of the way you need a bottoming tap. I solve the problem by putting the barrel in the lathe centering it, and undercutting the barrel to the thread outside diameter. This gives me a straight shoulder to fit the plug up against. Another solution I some times use is to make a brass bushing to fill up the gap. Whatever method you use you want to have the plug solid against the sholder. You don't want a gap. :idunno:

 

[Bill Hall]

I use a combination of a homemade bottoming tap and chamfering the end of the plug. I bought a 3/4-16 tap that I used once to cut the threads from scratch, then ground it flat to complete the threads in the breech recess. Now I use it routinely the help clean out the threads. You need to be careful using a homeground bottoming tap, as the front teeth are prone to chipping, and it still doesn't cut viable threads all the way to the shoulder, but it helps. I finish the job by cutting just enough chamfer on the end of the threads to cause the breechplug face to squish against the shoulder in the bore. I use magic marker on the breechplug face to indicate when the face and shoulder mate up. The black ink will smear off when there is contact. Bill

 

[jtpotter]

I just got done breeching my barrel, I used the file the little burr, re-install, file little burr method. This was the first time I have ever breeched a barrel and it was easy,quick and I am very pleased with the results.
I believe if you bottom tap the barrel, you would still have to file the little burr etc...
A bottom tap still has a slight taper on the first thread of the tap, I'm pretty sure.

 

[jtpotter]

Not trying to steal the original thread, but I do have a question.(sorry if this isn't proper ettiquite, I'm also new to forums)
I have a .54 cal Green Mountain barrel, with 5/8-18 threads. There was'nt much of a shoulder for the breech to seat against. I stopped when I knew the breech plug was touching all the rifling and the top facet of barrel was close to matching top flat of the breech plug. I really had to crank it in to make the flats meet with each other. When I remove the plug for inletting, will it match up again? I did mark the bottom flats of barrel and plug. I also draw filed the two pieces, looks awesome! Thanks - If it wasn't proper to post a question in someone elses topic, PLEASE let me know!

 

[jdkerstetter]

Your fine posting here in my opinion. Your question is far from hi-jacking a thread compared to others I've seen here. Heck, I've been know to participate. :grin:

A .54 caliber with a 5/8 plug will not have much shoulder, but you don't need much to make the seal. They would not have produced it that way if it were unsafe...you are fine there.

I take it you haven't removed it since you cranked it down to line up the flats. I guess I don't understand your concern completely. You are going to remove it again regardless, right? If it's not inlet yet you are far from finishing the gun.

If you got it to line up once it will line up again. The question is, did you gall any threads torquing it down? I would remove it before I went any farther just to be sure. It is probably OK, but I would just double check.

Enjoy, J.D.

 

[ApprenticeBuilder]

You will be fine, as long as your witness marks are on the bottom flat and you have both barrel and plug marked, I always put a pair of witness marks, works easiest for me.

 

[ApprenticeBuilder]

I made my own bottoming tap, I have done every barrel I've breached that way as thats how I was taught. Each time I do a different size plug I make a new tap.

 

[Zonie]

I file off the first thread with a flat file.

When doing this, I carefully rotate the thread as I'm filing so the thread is gradually removed down to the bottom of the threads "V".

I only remove enough of the threads to clear the unthreaded area in the barrel.
This leaves the fully engaged threads to retain the breech plug.

 

[ApprenticeBuilder]

For me,

its easier to cut threads full depth than it is trying to file a near perfect bevel on the round end of a breach plug, I don't have to worry about flat spots on the threads.

:wink:

 

[Birddog6]

It will stop at the witness mark if You stop there. Getz barrel company & has been doing that cal. & plug size for years.(& still does) Personally I don't like it, as I like a shoulder at the plug/bore fit & have several of them rebreeched to a larger plug in this instance. It is a just matter of preference. Allot of fouler barrels are done that way, no face fit at the breech, the breechplug simply threads into the barrel. Allot of originals are that way as well & when taken about, you wonder how the plug even stayed in because they are so loose & such a sloppy fit. :shocked2:

I would use AntiSieze on the threads in the hole & on the plug as well. Putting some IN the hole lubricates the threads in the hole & pushes the AntiSieze forward of the plug on the threads & lubes the plug as it goes in, so ALL of the threads are lubed & less chance of galding.

Keith Lisle

 

[jdkerstetter]

....I would use AntiSieze on the threads in the hole & on the plug as well.... Keith Lisle

Hopefully he did this on intial install. If not, I also consider it a must do on the reinstall. I should have mentioned antisieze. Good catch Keith.

Enjoy, J.D.

 

[mogrene]

I've been using 3-in-1 oil to lubricate the threads while working the plug. That seems to work fine. I realize I'll need something more substantial when I do the final seating.

Speaking of anti-seize: Alexander suggests a home-made concoction of petroleum jelley and graphite. Does anyone have any experience with this? Or is a tube of store-bought anti-seize the best option?

Rick

 

[mogrene]

JT:

Certainly no problem from my end - thanks for adding.

Rick

 

[jdkerstetter]

Speaking of anti-seize: Alexander suggests a home-made concoction of petroleum jelley and graphite.

Yea, that was always one of his tips that made me laugh. Supply lines must long up there in Canada. He sure did stick a lot of things in his book that didn't need to be there....good book, but sometimes he muddies up the water a little too much.

Never tried it but don't see why it wouldn't work. You can get a life time supply at any hardware or auto parts store or almost anywhere, for a couple bucks....and it comes in it's own tube. :wink:

Enjoy, J.D.

 

[Robby]

I use drafting pencils, only the shaft of graphite is sharpened. My first M/L I mixed some with petroleum jelly for the breech threads. It worked great and I still use it. At the time I had never heard of Mr. Alexander, well pretty much anybody else either.
Maybe I'll write a book, "Building Left Handed Guns for Right Thinking People", never mind, just hold Mr. Alexanders book to a mirror. :grin:
Robby