First Gun Build Questions

[jdkerstetter]

Great article. Print it and stick it in your new copy of The Gunsmith of Greenville County.

As far as the measurements are concerned, as I said before, you need a dial or digital caliper.

Notched plugs? What this refers to is a notch in the face of the plug to allow the vent hole to be drilled farther back on the barrel....a channel cut to allow a path to the powder.

Example; Take for instance the Sharon barrel I have with the 3/4" breech plug. Allowing 3/16" to the center of a vent liner, the pan on my lock would have to be 15/16" from the back of the barrel. This would look horrible once the gun was assembled as I would never get proper wrist architecture...there would be long hump behind the lock fence.

The alternatives are to shorten the plug and the end of the barrel to match (which I will do) or notch the face so the vent could be drilled back farther on the barrel to move the lock back.

The notch on the face of the plug would be in the threaded protion of the barrel....that and the channel itself would create a fouling trap and eventual gas checking of the plug/breech area.

Some will argue it was done on originals so it must be OK. Some still do it. Many do not. There's more information on it here and on other sites if you are inclined to look.

Enjoy, J.D.

 

Already added to my book.

Couldn't you also just [strike]notch[/strike] extend the barrel channel back a fraction to make it all line up (or is that what you mean when you say notch the face)?

I wish there was a good video that showed all this stuff. I bought the Video by James Turpin, but he skips over a lot of the details such as this. Was there one made that is better or are there some online? I've struck out on YouTube, but there is just tons of stuff there and trying to find the right search parameter is sometimes mind boggling.

 

[jdkerstetter]

Here is a link to a tutorial by a 'smith who notches his breech plugs: http://hootalrifleshop.org/install_flashliner.htm

He claims no ill effects. I choose not to do it unless there is no other way around it.

You may find some other useful information on his site by clicking on the tabs at the top.

As far as videos on gun building go, I don't own any so can't recommend any. Books a plenty but no videos.

Enjoy, J.D.

 

Okay, so this is strange. The breech plug length is 0.611", and the barrel inlet for the plug is 0.625", but when I thread the plug into the barrel, it bottoms out before the shoulder mates with the barrel.

I should have the permatex tomorrow, so I'm not going to start filling it just yet, but it seems strange that the plug is shorter than the barrel and yet bottoms out.

Should I be looking in the barre to see if something funny is going on that is preventing it from seating all the way? If the breech is truly just a hair shorter than the barrel inlet, then I would presume I need to file the barrel just slightly.

 

[Zonie]

Do NOT shorten the plug at this stage.

The reason it bottoms out is the threads are not cut to the full depth of the hole.

This is fairly typical and it is easy to deal with.

Screw in the breech plug intil it stops.
Measure the gap between the rear faces of the breech plug and the rear of the barrel.

It will probably be about 1/8 inch.

Remove the breech plug and eyeball the threads on the plug. You will need to file off about 1/8" of them.

When you file them, try not to damage the threads further from the face than your measurement.

File off the sharp crest of the first one or two threads just a little bit. Then, rotate the plug and repeat.

Keep on doing this filing and rotating until you have removed the threads down to the bottom of the V's. Do not remove any material below this thread bottom (root diameter).

You should end up with a plug which has threads starting where the barrel threads end but it doesn't hurt to remove maybe 1/2 or 3/4 of the next threads V to get a little clearance down there.

When your finished getting the plug to screw in all the way without the threads interfereing, then you can start finding out what material needs to be removed to get the plug fully installed.

 

WTH.... which threads are not cut to the full depth? The threads on the plug or the ones in the barrel?

 

[Zonie]

The threads in the rear of the barrel are seldom cut all the way to the shoulder where the breech plug will seal.

To fully cut them to full depth takes a bottom tap and these often have to be run in by hand.

This is not practical for the barrel maker so they thread the hole almost, but not fully to the shoulder.

The threads on the outer end of the breech plug are the ones you will need to remove.

 

It's way less than 1/8". It's more like 1mm which is 0.0393701" I can hardly measure that.

Also, on the Green Mountain barrel, is the flat that has the caliber and makers mark the flat that I want either up or down in the barrel channel due to runout?

I'm not messing with anything until tomorrow. Kind of scared I'm gonna mess it up, and not 100% sure what you are instructing Zonie. I think you are saying to keep the diameter of the plug the same, but remove the threads for 1mm of it. Hell, I don't even think that is even one thread.

 

[jdkerstetter]

Also, on the Green Mountain barrel, is the flat that has the caliber and makers mark the flat that I want either up or down in the barrel channel due to runout?

There should be no runout in GM barrel...or any barrel manufactured today that I know of for that matter...unless somebody really screwed up.

The runout you are reading about (In The Gunsmith of Greenville County, I assume) was fairly common in the old Douglas barrels. Those barrels where drilled in octagon blanks and sometimes the drill bit wandered causing the hole in one end to not be centered...runout. Barrels today are bored and then the external shape is machined with the bore set on centers to avoid this. So...it doesn't matter where the GM logo ends up for functionality but most perfer it on one of the bottom 3 flats to hide it in the stock after assembly.

I think you are saying to keep the diameter of the plug the same, but remove the threads for 1mm of it.

Perhaps somebody has a picture that they can post for you. I looked and don't. Don't know that I can explain it any better than Zonie.

Good idea waiting. J.D.

 

[Zonie]

When you screw your new breech plug into the rear of the barrel, it will usually stop before the two rear surfaces on either side of the threaded plug reach the rear of the barrel.

There can be two reasons for this.

Either the face of the breech plug is hitting the shoulder in the barrel where the bore stops and the threads start, or, the threads on the end of the breech plug have bottomed on the last full thread inside the breech of the barrel.

Every gun I've built had the threads on the breech plug, which extended all the way forward to the face of the breech plug bottoming out on the deepest of the barrels threads.

By removing the thread at the nose (or face) of the breech plug the threads would no longer interfere and the plug could be screwed in until the face of the breech plug stopped on the shoulder at the bottom of the barrels hole.

In order to determine which condition exists, lightly cover the end face of the breech plug with inletting black or your wife's lipstick.

Screw the plug in until it stops on something.

Remove the plug and look at the end face of the breech plug.

If the inletting black or lipstick is undamaged and shows no marks, the threads are bottoming out.

If the inletting black or lipstick shows circular rub marks, the threads are OK but the plug is too long.

If there is only a 1mm gap between the end of the barrel and the shoulders of the breech plug then you don't have too much work to do.

Just remember, when the plug is fully installed, three things have to happen at the same time.

1. The face of the breech plug must be tight against the shoulder where the bore ends.

2. The top surface of the tang must be in line with one of the flats on the barrel so it looks like a continuation of the barrel flat.

3. The two shoulders adjacent to the threads on the breech plug should be tight against the outer end of the barrel.
The lower (concealed) shoulder might have a small gap but the top shoulder should be tight against the rear of the barrel.
If it is not, it will look like the breech plug is not fully installed and this joint is always visible to anyone who looks at the gun.

 

Thanks guys... I think I understand what is being said, and I apreciate all the help. I think I just convinced myself of why I should buy a premium membership here as the advice I have received is awesome.

Let me ask this though.

1) When I file off a bit of the threads to get in to go in all the way, and since the plug is a hair shorter than the depth of the breech of the barrel, will I need to still mill down the barrel to ensure there is no gap between the shoulder and the breech, or is the amount of difference (0.014") insignificant enough that the gap will be safe?

2) Since I am only talking 1mm, I assume we are not talking using a bastard file to file this little amount of thread off, but more of a needle file? I have both, but just want to make sure I'm using the right too for the job. I'd hate to have to drive all the way back to Lodi for a new breech plug.

 

[jdkerstetter]

(1) When I file off a bit of the threads to get in to go in all the way, and since the plug is a hair shorter than the depth of the breech of the barrel, will I need to still mill down the barrel to ensure there is no gap between the shoulder and the breech, or is the amount of difference (0.014") insignificant enough that the gap will be safe?

No such thing as an insignificant gap in this case. You want a tight seal/crush fit between the face of the plug and the shoulder in the breech (where the threads stop and the rifled area begins). This is what seals the breech, not the threads. If there is no seal you could get gas checking of the threads and eventual leakage. Furthermore, if there is a gap there you will form a fowling trap where water and burnt residue can sit and...you get the picture.

(2) Since I am only talking 1mm, I assume we are not talking using a bastard file to file this little amount of thread off, but more of a needle file? I have both, but just want to make sure I'm using the right too for the job. I'd hate to have to drive all the way back to Lodi for a new breech plug.

Since you are taking that 1mm down across the entire face of the plug & back of the barrel a wide, flat file is the right tool as it will help keep everything flat and square. Your files should fit the surface. Needle files are best left to small parts and detail work.

Don't forget to periodically check those areas you are filing for square also...or you will have a gap on one side or the other.

Enjoy, J.D.

 

JD, I thought I was filing off part (1mm) of the threads, not the face of the plug. If that is the case, I don't see how a large flat file would work since I am working on the side of the plug.

 

[jdkerstetter]

You'll be filing all three surfaces so if you don't specify I can't keep up.

Regardless, I wouldn't use a needle file for the job. It's easier to control a standard file as you can get a full grip on the handle and used both hands...one fore and one aft.

Enjoy, J.D.

 

[don hepler]

I was a machinist for 40+ years. Listen to what Zonie is telling you. Keep reading his posts and the reference from TOTW. Read the part about retapping the threads in the breech of the barrel with a bottom tap.

Do you know any machinist? They would be very helpful. It's very difficult to explain without pictures.

You have a smooth surface on the breech plug in front of the threads, and you have a smooth surface at the back of the threads, where the hex is. Inside the barrel is a smooth surface at the bottom of the threads. As Zonie has said you want the front suface of the breech plug to hit the bottom surface (in the barrel) at the same time lining up and touching the back surface of the barrel. In machinist terms these smooth surfaces are refered to as "faces". And of course the breech plug flat needs to match up with the barrel flats.Don't worry just keep asking and we'll try to help. Just solve this one issue, then we'll move on.

You have 18 threads for every inch of threads, If you divide 18 into 1.00 it comes out to .05555 per thread,(rounded to .056).Take .056 divided by 8(number of flats on barrel)you will get .007. If the gap is .035(for example)it would take 5 indexes of the flats to close the gap. Just keep reading the TOTW and what Zonie is saying, and it will jump out and you'll be saying, sounds simple.

Try It, and good luck.

 

[crockett]

Zonie- these are problems I've never thought much about. What about getting a bottoming tap and threading the barrel all the way to the shoulder? What do you do if you thread in the breech plug and it bottoms against the shoulder but the flats are lined up?

 

Thanks Hadden, JD and Zonie... I appreciate all the help. I feel like a complete PITA with all these questions. I'm glad you are not bothered with them.

Unfortunately, I don't know a machinist, but I think I understand what you all are tell me. Worst off, if i mess it up, I'm only looking at another $20 or so for a new breech plug, not $100+ for a new barrel.

As far as how many turns I need to align with the next flat, I'm almost there, so hopefully the little bit I need to take off will bring it home, but then I have to deal with the difference between the plug face and the shoulder. I'll just take it one step at a time and I'll appreciate the whole learning process.

 

[jdkerstetter]

...I feel like a complete PITA with all these questions. I'm glad you are not bothered with them.....

Who says we're not bothered with them?!?! :haha: It's pay back for all the folks who put up with us "learning".... :wink: ....

...and we're all still learning. You're welcome :thumbsup: , J.D.

 

Wahoo!!! I think I got it. It's seated on the flat, and nice and tight. The inner shoulder seats nice all the way around on the plug too. The only issue is, there is just a tiny hair gap between the barrel and the breech shoulder. If it's purely cosmetics, I don't think anyone would see it. If it's a safety issue, I can do some more filing, but I will have to go to the next flat since it is dead on with this flat.

 

[jdkerstetter]

Your gap there is at the breech plug tang and on the bottom the breech plug bolster will also have a gap.

That's the nature of the game. Keep going and close up that gap. That's what we've been talkin' about all these post:

(1) Tight seal/crush fit between the breech plug face and the shoulder in the breech itself.

(2) Alignment of tang with one of the top 5 flats and...

(3) Breech plug tang and bolster tight up against the end of the barrel.

You're almost there! J.D.