Breech plug fitting?

[alaskasmoker]

So Im having a hard time understanding breech plug fitting. What do you remove material from to make the plug line up with the flats?

Do you file the breech end of the barrel, or do you measure depth of threads and hack off threads on plug pretty close then file away?

 

[paulvallandigham]

When the back of the barrel is drilled and threaded for your breechplug, the drill is not Square to the side of the bore, but angled, like most drill bits. You therefore have a slight bevel in front of the threads before you get to the back of the rifling.

Threading is also done with standard, tapered dies, so you also have threads that are not cut all the way to the front of the threaded area to the same depth. You will need to make or use a " bottoming tap", to clean up those threads all the way to the front of that threaded portion.

Now, because of the bevel, you need to file a bevel around the front of the plug, that will remove the first two threads of the plug. Then angle will be about 22 degrees I believe, but you can check the angle by checking a drill bit that is about as large as the hole in your barrel.

You may also have to shorten the back of the barrel, and the front of the plug, to fit the barrel to your specific action.

Inlet the barrel, without the breechplug in it, into the stock, completely, and then mark out the position of your lockplate, before determining where and how long the threaded portion of the plug needs to be. Most barrel makers make the back end longer than needed so you can fit the barrel to your needs. The same is done by the makers of breechplugs- they are also longer than you need, so you can fit them to your specific barrel and needs.

The shortening work can be done with a draw file, or end mill, or a lathe, if you have them. Measure twice and cut one. Use marking dye( Prussion Blue) on the piece to help you check your progress, and to show up the lines you marks to guide your work.

 

[alaskasmoker]

Thanks! Alot of that makes sense now, Except for this... "Inlet the barrel, without the breechplug in it, into the stock, completely, and then mark out the position of your lockplate, before determining where and how long the threaded portion of the plug needs to be. "

What does it matter where the threads of the breech plug are or how long they need to be?


And if it matters in your tips, Im using a pre inletted stock, lock and channel.

Thanks again!

 

[paulvallandigham]

If you are building a flintlock, and some percussion lock guns, you need to place the hole for the drum or vent in the barrel to center on your lockplate. You don't want that vent hole or drum drilling into the threads of a too long breechplugs. So, figure out the position of the lockplate to the back of the barrel, then the position of the hole for the vent or drum, and use that to determine how much of the back of the barrel, if any, needs to be shortened with a file, or power tool. Its typical for modern barrels to have between 1/16- 1/4" more length than is necessary, so that the barrel can be adjusted by shortening the rear of the barrel, to fit given plugs, and locks.

That will also tell you how long the threaded portion of the plug needs to be, to give you clearance for the vent liner, or from the drum for your nipple. So, if your plug and barrel will put the vent hole too far forward of where the center of the flashpan on your lock would be, you can shorten the barrel, and then the front of the breechplug, to move that vent hole back to the center of your flashpan.

I like to have 1/8"( .125") of clearance between the face of the breechplug, and the rear EDGE of the vent hole in a flintlock. that means, if you use the CENTER of the VENT HOLE, that you have to add 1/2 the diameter of that vent hole to that 1/8" allowance. to get your inside bore distance for the vent's location.

On percussion guns, I don't want the drum drilling into the threads. That weakens both the thread of the plug, and the thread of the drum. I also don't like having to file or cut a groove into the face of the plug to provide a channel for flame from the percussion cap to reach the powder charge. That makes cleaning off that face more difficult, and requires that the channel be cleaned by using a pipe clean through the cleanout screw in the drum. I don't want to have to remove a clean-out screw in the field to get the gun firing again! The best way I know to NOT have to fiddle with my clean-out screw is to mount the drum so that its threads are in front of the breechplug.

YOu only need 1/2" of threaded plug to provide all the strength needed to resist the pressures in the powder chamber when the gun is fired. Most of the plugs made today are as long as 3/4" and that makes fitting that lock to the barrel difficult, if the gunbuilder doesn't know to adjust both the plug and the back of the barrel to his lockplate's dimensions.

Your Lock controls everything else about the gun- the position of the barrel, the trigger, even the buttstock. The lock is where the Action IS! :hatsoff: :hatsoff:

 

[Birddog6]

Inlet the barrel, without the breechplug in it, into the stock, completely, and then mark out the position of your lockplate, before determining where and how long the threaded portion of the plug needs to be.

IMHO you breech the barrel how you want it & so you KNOW where the end of the breechplug is exactly before you inlet the barrel. You do the barrel first & shorten the breechplug & etc. first. Then you inlet the lock about 75-90% of the way on a precarve, as the lock is where they set it up to be. THEN you remove the breechplug (that you have all cut, fitted) & inlet the barrel to the proper place to align the vent hole you will make with the flashpan.

:thumbsup:

 

[chuck c.]

When you get ready to do your final fitting darken all contact surfaces (on the breech plug and barrel)with a black permanent marker. This will do two things. It will show you where contact is being made and allow you to only remove what metal is necessary. The other thing is that it helps you keep the file flat an square to the surface because the black surface allows you to see exactly how the metal is being removed by the file.Inlet black works pretty well when applied to the shoulder of the threads in the breech as an aid to let you know when you are making a complete seal. Just apply it to the shoulder with a small paint brush. You want the barrel's stampings on the bottom flat and a depth of about 1/2" or a little less. This combination is what will force you to remove metal from both the breech plug and the barrel. Proceed very slowly and expect to spend a lot of time on your first attempt, perhaps a day or more. You can have this done by a machinist for around $15 but you will learn a lot by doing it yourself. If you don't have a 15" cresent wrench, get one. Be careful not to mar any part of the breech plug or barrel with the wrench, thin brass shims in the jaws will help prevent that. When you get real close to a final fit stop! You will find that after a couple of times of removing and tightening that it will seat just a little deeper! There is a lot of people who know more about these things than I do, but if I can be of any further help please feel free to contact me. Also the thickness of the shoulder can make the job easier or harder. It's easier to do with a wide shoulder. If you have a narrow shoulder caused by a large bore in a small barrel you can continue one after the breech plug is properly seated because you are just crushing the narrow shoulder. Don't ask how I know that!

 

[BLAHMAN]

What does it matter where the threads of the breech plug are or how long they need to be?


And if it matters in your tips, Im using a pre inletted stock, lock and channel.

That's the hard way!

Here's a tip: tin the face of your breechplug with a dollop of solder....makes a "gasket" so to speak....good luck

 

[mikee51848]

If you're dealing with a pre-cut kit, you can fit the lock and barrel. Then put your rammer down the barrel and mark it where it meets the muzzle. Then lay the rammer on the top of the barrel and you'll know if the plug is in the right place. I personally, would hesitate on shortening the plug. Dixon's book has full explanations of where the touch hole should be placed, and what to do if the plug is too long.

 

[paulvallandigham]

"What does it matter where the threads of the breech plug are or how long they need to be?"
______________________________________________

If the plug is short of the rifling, there is a gap at the back of the barrel, and in front of the breechplug face, where crud builds, and corrodes the barrel.

That is a very dangerous situation over a number of years. Think where that barrel will rupture and how close it is to your face and hands.

The guy who built my .50 caliber rifle screwed this up, leaving a gap about 1/8" wide in front of the plug.

Thankfully, I decided to convert the rifle from percussion to Flint about a year later, and the gunmaker who did that work removed the breechplug, and discovered the mess! The corrosion was there, but not deep enough to be a danger, yet.

I had some idea that the barrel was not right, because no matter how much soaking and pumping, and cleaning and drying the barrel after shooting it, A dry patch run down to the breechplug face would always come back with a "ring " of black powder "stain" on the patch, as if there still was crud in the "corners" of the bore that I was not getting. Of course, I used a scraper to try to get this, too, but that didn't work, either. When we put a light down the bore, the plug looked bright and clean, as did the barrel and grooves. So, where was that crud coming from?

We ordered a new Breechplug, and its threaded portion was actually shorter than the threads on my older one! That is when I found out that there is no consistency in plug length in the industry. And that is when a phone call to the barrel maker- to see if he had a plug the correct length-- alerted me to the fact that extra length was routinely left at the back of the barrel, with the expectation that the gunbuilder would file it down to get the correct fit.

IT IS TRADITIONAL that barrel makers stamp their marks on the flat that represents the side of the run-out, so that the run-out is going down. Then, the builder can correct the problem with a higher front sight!


Today, most barrel run-out is either very small- much better boring equipment-- or non-existent, as the barrelstock is first bored and rifled, and then the flats are cut with the barrel held on centers in the bore, eliminating any run-out that existed at the end of the boring process.Its not uncommon for barrels made this way to have NO stamp or mark on a flat, other than the company's name, and it doesn't matter which flat is placed down. Out of tradition, most builders continue to orient the barrel, so the manufacturer's name is on the bottom flat of the gun.

When barrels were forged, the flats were forged first, and then filed on the barrel, BEFORE the bore was drilled. If the drill bit hit anything in the steel blank, the bit could turn and would then drill off-center, leaving "run-out". Run out is simply the difference from "square " of the bore to the outside diameter of the barrel. If the bore is drilled straight, it will be parallel and " Square to the outside diameter and dimensions of the barrel.