Question on issues with breech plug fitting

[HighUintas]

I made my first attempt at fitting a breech plug last night. I spent about 4 hours on it and nearly nailed it, but in the final filing of the plug face I took just a tad too much off one side and will end up having to go to the next flat.

I have two questions. The first is concerning the barrel breech threads furthest in the barrel from the breech just before the counter step. There's a couple of, I guess you could call them burrs but they're more like lumps, in the very last bit of threads in the barrel which tends to want to Gall up my plug threads when I get it to the point of being tightened. When first putting the breech plug in, I wasn't able to get any color transfer to the breech plug because the plug would stop in the threads at the point of the burrs. I have no way of filing those out because I don't have a 90° needle file and even if I did, I don't know if I could actually fix the thread because it seems to be more than just burrs.. it's a pretty poor thread cut in the last 1/3 to half turn. So in order to get the breech plug to bottom out, I had to file off the first third of turn or so of thread on the plug. This is very hard to explain in text. I think it's not just that there's a couple of poor threads the very bottom of the barrel, but it seems like the barrel threads dont go 100% of the way to the counter step, so I have to have a small portion of my breech plug that is nearest the face unthreaded.

Is it common to have to have a small portion near the plug face threadless? Also, are the barrel threads something I should call colerain about and see if they are willing to fix the threads or re-breach it if necessary? Is there a way I can fix them? I don't have a 3/4-16 tap or a 90 deg needle file

The second question is, what is the minimum amount of thread engagement necessary to provide adequate strength and safety? Because I have to now go to the next flat and file off more material and the fact that I have the very small portion near the breach plug face unthreaded, I'm worried that I won't have enough threat engagement.

Pictures are below. You can see the threadless portion near the face and the buggered up and rounded last thread. All help is appreciated!

 

[dave_person]

Hi,
First, don't be worried very much about the threads. Most original plugs were no more than 1/2" deep and many had pretty crudely fit threads. Modern plugs that are usually 5/8" deep have plenty of extra depth to file away if required. There commonly are very shallow or no threads at the bottom of the hole against the shoulder. It is OK to hand file that first thread on the plug down so it can screw fully into place. You can do that by hand, just try to file it as evenly around as you can but don't obsess about it. Also, don't make the plug so tight that you really have to force it into place. If you really tightened it down hard and moved it slightly past your target flat, just back it off that tiny bit so it lines up and call it done. You will be fine.

dave

 

[rdane]

Dave said it right.

 

[deerstalkert]

a possible way to smooth out the last thread is to go to the local hardware and find a 3/4x16 schedule 8 bolt. grind the face perfectly flat. run it in the breech a few times , gently snugging it up against the shoulder, GENTLY is important. don't want to gall or set the threads back any.
the hard sch8 should smooth out the boogers.

 

[HighUintas]

Thank you @dave_person and @deerstalkert . Great advice and I appreciate it. I was getting worried I'd have to get a new plug and send my barrel out! My confidence is back.

As a side note, my technique for filing the plug face was to alternate by 90 degrees making sure to remove all file marks to try to keep it as even and square as possible. I still found it fairly difficult to keep the whole face filed evenly flat and ended up using the inletting type technique only removing the transfer color in order to gain full contact. I was using an 8" mill file.

Is there a more clever way of filing to ensure I'm keeping the face even and square?

 

[deerstalkert]

one way is to put a washer on the plug and thread the plug into the breech, leaving space for a file. use a safe file without cutting teeth on the washer side and no teeth on the edge against the threads of the plug.
snug the plug up to the file and rotate the file around the plug in the tightening direction. works but the dye transfer method does too.

 

[Vaino]

I've never built a MLer w/ 5/8" long threaded plug. ....always made them 1/2" long. To ensure the end of the plug contacted the shoulder, I bought 2 taps for both of the tap sizes I used and made a flat bottom tap out of them to ensure that the threaded plug contacted the shoulder w/o a big chamfer on the end of the plug. This was common when the bore dia and threaded dia resulted in a very narrow shoulder. .....Fred

 

[HighUintas]

one way is to put a washer on the plug and thread the plug into the breech, leaving space for a file. use a safe file without cutting teeth on the washer side and no teeth on the edge against the threads of the plug.
snug the plug up to the file and rotate the file around the plug in the tightening direction. works but the dye transfer method does too.

That's a good idea. That's for keeping the barrel breech square though, correct? I was having trouble keeping the breach plug face square as I was filing it down. I couldn't think of any way to make that easier except for trying a 10 in file so that it would be wider.

 

[HighUintas]

I've never built a MLer w/ 5/8" long threaded plug. ....always made them 1/2" long. To ensure the end of the plug contacted the shoulder, I bought 2 taps for both of the tap sizes I used and made a flat bottom tap out of them to ensure that the threaded plug contacted the shoulder w/o a big chamfer on the end of the plug. This was common when the bore dia and threaded dia resulted in a very narrow shoulder. .....Fred

That is also a good idea. I was just in the hardware store and they did have a 3/4 16 bottoming tap but even that had a slight taper on the end that would probably cut about the same as the threads that are currently in my barrel.

I was deciding between a rice and a colerain, and the rice had a 5/8 18 breach.. wishing I would have went without one to get that larger with counter step.

Anyway, I'll get her done. Hopefully this evening!

 

[dave_person]

Hi,
Your method of filing the front of the plug is fine. It does not have to be perfect. Alternating the direction of filing 90 degrees is exactly correct for hand filing a flat surface. I also hand file a chamfer around the edges of the face to accommodate those shallow or lost threads. I just do it carefully and as evenly as I can, and then use Prussian blue, magic marker, or inletting black to transfer color where it touches the shoulder and file away those corresponding spots on the plug until it fits evenly. However, it is a bit of an art because you want the target flat to line up so go slow and if you don't have perfect contact when the flat lines up but you are close, call it good. If anyone questions you on that, tell them to look at a plug from an original long rifle. It will scare the hell out of them.

dave

 

[The Crisco Kid]

Any thoughts on using blue locktite on the very end of the plug to seal junction at the shoulder?

 

[HighUintas]

Hi,
Your method of filing the front of the plug is fine. It does not have to be perfect. Alternating the direction of filing 90 degrees is exactly correct for hand filing a flat surface. I also hand file a chamfer around the edges of the face to accommodate those shallow or lost threads. I just do it carefully and as evenly as I can, and then use Prussian blue, magic marker, or inletting black to transfer color where it touches the shoulder and file away those corresponding spots on the plug until it fits evenly. However, it is a bit of an art because you want the target flat to line up so go slow and if you don't have perfect contact when the flat lines up but you are close, call it good. If anyone questions you on that, tell them to look at a plug from an original long rifle. It will scare the hell out of them.

dave

Thanks, Dave. Your expertise is appreciated!

And based on your statement of calling it good if contact is really close to perfect when the flats line up, I could have called it good last night but then continued on a little way to hit the next flat in pursuit of perfect contact

I'm learning and it's fun, so doing it again doesn't bother me one bit!

 

[HighUintas]

Here's where I'm at now. This is tightened fairly snug with an 8-in adjustable wrench, but I didn't put all my weight into it. I have contact on the breech plug bolster surface and contact all the way around the face of the plug but it looks like fairly light contact on the face. It sounds like nobody really agrees on how much torque to put on a breach plug. Do you think I'd be able to turn it the last little bit with a bigger wrench to get the flats lined up?

 

[deerstalkert]

take 1 -2 more licks on the upper tang face, it looks like no contact on the heel yet. light contact on the plug face.
you da man! wish my file work looked that good. of course it does to my old eyes without my glasses

 

[HighUintas]

take 1 -2 more licks on the upper tang face, it looks like no contact on the heel yet. light contact on the plug face.
you da man! wish my file work looked that good. of course it does to my old eyes without my glasses

Thanks! By licks do you mean file a bit more off the upper tang mating surface? I was actually going to just not worry about the lower tang mating surface since that portion won't be visible and I couldn't think of a mechanical reason why the lower surface needs to be in contact with the barrel breech. Am I missing something there?

I was thinking I might use 400 grit wet/dry paper on the upper portion of the barrel breech to get that last tiny bit off for better plug face contact and timing the flats so that I don't take too much off with a file. The file removes so much so quickly it scares me haha

 

[The Crisco Kid]

If you tighten and loosen it a few times the metal should compress enough to gain the little that you need to line up. It all looks good from here.

 

[HighUintas]

An interesting thing I have found in filing these surfaces alternating 90 degrees is that the side that I am pushing towards ends up having more taken off than the side closer to me, I guess due to my green file skills. I found that if after change direction by 90 degrees I then rotate the plug by 180 and do the same thing, I can make the surface more even due to have the opposite side of the plug away from me.

 

[deerstalkert]

yes licks are meant as strokes. only reason for full contact is if there is some flex between the barrel and the tang, it could lead to tang breaking. totally outside chance but you have done such a marvelous job with achieving full timing on the plug i thought it might get it solid .
like the crisco kid says. a few torques and you probably have it aligned.
going back to bed now. typing tired me out.

 

[deerstalkert]

stroke only half way with your file and concentrate on lifting at the end of the stroke. i have made many an egg in my life.

 

[Kansas Kid]

It’s hard to tell from here but polish the breech face to a mirror finish and you will never need a bore light and it will clean easy. Just shine a small light down the bore and it will reflect very well. Probably tightening and loosening a few times and it will be there. Looks good for now.