Fitting breech plug?

[Deuce50]

Well I have started my first rifle build and ran into a dilemma right out of the gate.  I'm using a straight green mountain barrel and a hooked breech plug, PLUG-FHG-16-3.  I threaded the plug in and it stopped .075" short and was not touching the bottom of the thread bore.  Upon closer inspection, the breech plug threads are not threaded all the way to the bottom of the bore and the breech plug is cut it's entire length.  Is this typical?  I'm assuming I need to file a chamber on the last threads of the breech plug?

[rich pierce]

I’d want to run a bottoming tap into the breech. There is often a bit of a chamfer at the end of a breechplug.

[Deuce50]

I’d want to run a bottoming tap into the breech. There is often a bit of a chamfer at the end of a breechplug.

I thought of that, but a tap that size would be quite expensive for only using it one time.  I was thinking this is a common occurance and clambering the plug was the accepted remedy.

[rich pierce]

What size tap?

[Deuce50]

3/4 - 16

[rich pierce]

I don’t have a bottoming tap in 3/4-16. Just a plug tap. Have you fitted breechplugs before?

[Deuce50]

No sir, but I have tapped many hole in my machining days.  It definitely is stoping at the end of the threads shy of the bottom.  Even a bottom out tap won't cut threads the entire way to the wall at the bottom of the bore.  It looks like some plugs have a good side chamber them and the one I bought is sharp to the end.   

[rich pierce]

Sent you a PM. Yes it is impossible to get threads all the way. If you feel it’s well threaded I’d paint the end of the plug with Dykem or marker and hand file it.

Then you have to do the dance of trimming the barrel breech and the breechplug nose till the plug bottoms out just when the tang gets tight and aligns with the desired flat on the barrel.

[Deuce50]

Here's some pictures of what I'm up against.  You can see the plug is sharp to the end and also where the threads stop in the barrell.

[Blacksmoke]

Deuce50: Welcome to the forum!   A 3/4"X16 bottoming tap and a little chamfering of the last thread of the breech plug is in order to correct the problem.
 Also you can make your own bottoming tap out of a starting tap by doing a little grinding wheel work. Just grind the lead in threads back to the bottoming level and "Bobs" your uncle.     Hugh Toenjes

[Deuce50]

Deuce50: Welcome to the forum!   A 3/4"X16 bottoming tap and a little chamfering of the last thread of the breech plug is in order to correct the problem.
 Also you can make your own bottoming tap out of a starting tap by doing a little grinding wheel work. Just grind the lead in threads back to the bottoming level and "Bobs" your uncle.     Hugh Toenjes

Thanks black smoke.  Is this normal for the thread to stop just short of the bottom?  Is standard bottom top will always leave a little at the bottom.  Looks like if I take about one thread off the plug it might reach bottom.

[borderdogs]

Deuce,
Doing this job is my utmost least favorite thing to do. If you haven't had the dovetails cut  then you will not have the added  problem of trying to match a specific flat on the barrel. I use Dykem Blue on the barrel breech flat and on the plug then take a little off with a file and try it. If you use a crescent wench put some tape on the jaws they will mar the plug eventually. When I filed mine I would file in one direction then file perpendicular to it and check with a square to make sure it stayed square. Its not hard just time consuming. Using Dykem or even a magic marker on the spots you are filing will indicate whether you are taking more material off one side or another.
Rob

[rich pierce]

Most are going to look like this when fitted.


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[D. Taylor Sapergia]

As you are installing and removing the plug from your barrel during the fitting, be sure the jaws of your wrench do not go all the way to the top flat of your plug.  If you do, you'll round them off and ruin the tang.
Also, grip the barrel in safe jaws in a solid vise, FORWARD of the threaded hole.  Otherwise, you'll put un-necessary tension on the threads squeezing it in the vise.

[alyce-james]

Blacksmoke; Sir a new bottoming tap has a one and a half thread lead. (1 1/2) lead. Employed as a perishable tool/ maintenance grinder for six (6) years. Chamfer on a breech plug makes life much easier. Well said Hugh. Have a great dat. AJ. 

[Deuce50]

Blacksmoke; Sir a new bottoming tap has a one and a half thread lead. (1 1/2) lead. Employed as a perishable tool/ maintenance grinder for six (6) years. Chamfer on a breech plug makes life much easier. Well said Hugh. Have a great dat. AJ.

Thanks Alyce, this is what I'm getting at.  I believe they have already threaded the barrel with a bottom tap.  Even that can only get so close to the shoulder at the bottom of the bore.  While I may not be a bad idea to run a modified bottom tap in just to see if I can get the threads a little farther down, the breech plug itself is basically threaded the entire length.  I will take some more measurements later to see just how much of a chamfer I would need on the plug to get it to thread all the way with the bore as is and check back with you guys.

[Deuce50]

Most are going to look like this when fitted.


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Thanks rich...  this plug appears to have the bottom thread removed and the 2nd thread heavily chambered.  I think I just need to make mine look like this.  A few more measurements later should tell me if that's the way to go.

[rich pierce]

Most barrel makers really lever it home and there’s done squishing of chamfered threads at the face of the plug. Not the best way perhaps but gives a good seal. I’d prefer less stress on the threads. Here’s the face of that plug.

[Deuce50]

Well I decided to start filing threads off the breech plug to see how much it would take to bottom out.  I marked the threads with a Sharpe, tightened plug into barrel, removed and filed the contact spots.  Ended up filing about a thread and a half.  The plug is now making contact with the shoulder in the barrel.  Contact is the whole way around the face of the breech but it is spotty so I'll have to work on that. 
Well on to the next problem...  with the breech plug touching the stamp on the barrel is on one of the top 3 flats.  To be more specific the stamp is on the flat to the left of the top flat if you are looking from the rear.  So at least I only have to move it 2 flats.  I'm sure I'll have to keep filing threads down as I go to keep lowering the plug as I file it shorter.  I just hope there are enough threads left to keep a safe breech.  Originally there we're 9 threads including the lead thread.  Down to about 7.5 threads now.  I'll have to do some math to figure out how much I have to shorten the plug to turn it 2 flats and see where that leaves me.

[rich pierce]

Well it’s a 3/4 x 16 so one turn is 1/16” or 0.062” methinks. If that’s true then to go 1 flat is 1/8 of that or about 0.008” to be removed from both the breech face and the barrel.  2 flats would be about 0.015-0.016”. Not a lot.

[steven baker]

Hi there , would you consider using a machine bolt of the same thread as a dummy run .It maybe help full before you use the real plug, take care Steven.

[davec2]

On the old board, I posted a tool I had made up for easily trimming a breech plug to length.  It could be used in a lathe (or in a vise and the length of the plug trimmed with a file).  For this type of situation, I use the original tool to trim the plug length and a blind hole tool to trim the breech plug shoulder.  You need a lathe for the shoulder trimming, but they both make trimming a plug so much easier as it eliminates all the normal set up rigamarole to hold  an already formed breech plug in the lathe.  Here is the old post    http://americanlongrifles.org/old_board/index.php?topic=198.0

Here is a picture of the tool used to trim the plug length.





This one is for trimming the shoulder



Calculate how much to take off and get close.  Then it's a little trial and error, but these tools make it easy to trim the plug putting it back and forth into the lathe.

[Not English]

Deuce, don't worry about all hundredths and thousandths of an inch. You will need a bottoming tap ( make your own) and transfer color for the breech plug. You'll need to file a champfer on the breach plug. Color the face and cheampfer of the breach plug with a transfer color. Bottom it out in the barrel and look for shiny spots on the face of the breach plug. File off the shiny spot (high spot) and repeat. Eventually, you will end up with a shiny ring around the breach plug. If the orientation is not right you need to file off the face of the breachplug until the orientation is right. You may need to shorten the breach of the barrel if it extends beyond the breach plug on a hooked breach. Keep in mind that the old time gunsmiths considered 3-4 threads at the breach adequate. With modern steels, it's more than adequate. The other option is to draw file the barrel where the stamp is.

[Deuce50]

Well I have the breech plug touching the shoulder in the barrel and in a spot where the stamp on the outside of the barrel will be under the stock.  Breech plug face is making about 90 percent contact and the hook is aligned with the flat.  So I guess I'll have to go another flat.

When filing the face, do you file across the entire face with the edge of the file near where the contact marks stop or do you only file around the edge where it is making contact?

[Dphariss]

Sore bought bottoming taps won't tap close enough to the shoulder.
I grind them back so I only have to chamfer one thread on the plug.
There are three videos at this link. One on making a cutter that will deepen/true the inner shoulder with a hand brace  or electric drill and two on setting a breech in a full turn when the barrel maker failed to properly fit the breech and left a fouling trap of about .030". I.E. the barrel was drilled and tapped .030"+ deeper than the threaded portion was long.
The Rebreech 3 is the final lathe and hand work on the breech reset.
Dan
https://www.youtube.com/channel/UCujoLVaOA_nORWfcaHX7PXA