location of vent liner

[fho]

Where do you put the vent liner ahead of the breech plug? On the seam of the breech plug and the barrel or ahead, how much?

I am going to try to build a flint lock rifle. I shot precussion but do have my big 25 caliber flint.
thank you
Olie

 

[LRB]

Ideally, in front of the plug, but as close as you can get it without thread interference. Mark it, but do not drill it until you have the lock in place so that you can be sure of horizonal alinement of the vent hole, which should be at dead level with the top of the pan, or some like the bottom of the vent hole at dead level with the pan. If you go with the higher position, be sure that the frizzen will cover the vent hole.

 

[AZ-Robert]

Where do you put the vent liner ahead of the breech plug? On the seam of the breech plug and the barrel or ahead, how much?

Olie, if I understand your question right, the answer is "ahead, by an amount equal to the depth of the plug plus at least half the width of your liner."

That seam you are referring to is (I think) way aft of where you want to put that hole. Check this pic...
[url] http://www.trackofthewolf.com...bId=134&styleId=486&partNum=PLUG-ST-12-9[/url]

 

[fho]

The seam that I referred to is the line where the breech plug touches the barrel.On the width of the barrel, I was going to put the vent in the middle, so the center line of the vent is at the top of the pan or in-line with the top of the forarm. Is this right? I was going to put the vent 1/8 inch ahead of the breech plug or is this to close?

 

[fho]

The vent liner that I was going to use is a 5/16x32 liner from Track of the Wolf.

 

[crossstick1948]

There is some contreversy about this. I believe you should put the vent liner ahead of the breach plug, far enough ahead that you can put all the vent liner threads in the barrel and not in the breach threads. Many rifles have the vent hole at or behind the breach plug. After a few shots the build up of fouling on the face of the breach plug starts pluging up the vent hole. The problem with putting the vent liner ahead of the breach is the lock screw doesn't fit unless the back of the barrel is notched. Willy Bonot the gunsmith at Friendship breached a barrel for me and he shortened the breach threads by about 1/4 inch before fitting the breach plug. This allowed the vent liner to be placed properly. The effect of this system is to create a sump area behind the vent liner to catch fowling crums and buildup of fowling. I can shoot 50 to 60 shots without the fouling buildup causing problems.
Pete

 

[Zonie]

Unless I'm building a percussion gun and installing a drum with a 5/16 inch thread, I locate the touch hole about .140-.170 ahead of the face of the breech plug.
This allows me to use a liner with a 1/4-28 thread without the possibility of the tap hitting the face of the liner as it passes thru the barrel wall. The clearance between the outside of the tap and the breech plug face is .015-.045.
If I had a nice milling machine like some of the guys here do, I would shoot for .135 +/-.005.
That would give .005-.015 clearance.

I would suggest caution in reducing the length of the breech plug threads by as much as 1/4 inch.
Although the threads on an existing plug are more than strong enough for the stresses envolved, removing them (for whatever reason) does weaken them and these threads must resist not only the forces resulting from tightening the plug into the barrel, but the force of the powder gas as well.

For example, using the greatest pressure I see in the Lyman Black Powder Handbook for a .50 cal projectile, the chamber pressure can be as much as 26,400 PSI.
The threads for a .50 cal barrel are often 3/4-16. That much pressure exerted against that thread will create a force of 11,663 pounds so the threads must be capable of resisting that much plus perhaps another 7 or 8 thousand more pounds due to tightening the breech plug so that the flats line up nicely.
If the threads are reduced in length it may effect the threads ability to resist this total load of perhaps 19,000 pounds.
If that happens, the breech plug may blow out and speaking for myself, I know my head isn't capable of stopping it's rearward flight. :hmm:

 

[Vaino]

Most breechplugs have excellent thread engagement and number of threads and to "blow out" the plug, a pressure far beyond that generated by black powder is req'd. Pressure takes the path of least resistance and the least resistive path is pushing the ball down the barrel, not "blowing" the steel plug out. In many cases I "violate" the breech plug threads when installing the TH liner because of lock placement and shape the end of the plug to suit. Have put some "huge" loads thru such an arrangement and have never experienced any leakage or ill effects what-so-ever.......Fred

 

[paulvallandigham]

also remember that that touch hole also relieves a lot of the chamber pressure in a Flintlock. I owuld be more concerned with the condition of the threads of the TH liner, and whether high pressure might blow the TH liner out of the gun, than the breechplug. However, I am not going to reduce the number of threads on the plug to on or two turns, either. Considering the coarse size of threads found on plugs, I think you can rely on the steel to withstand considerably more pressure than any BP load can generate, assuming the breechplug is properly fitted to the barrel.

 

[coldfoot]

I do the same thing as Willy as I cut off the end of the bbl about 1/4". The problem is that many locks like the Siler have about only 7/16" between the "fence" (the vertical piece of steel behind the pan) and the center of the lock's pan. Since the fence is typically aligned with the breech end of the bbl, you are limited to less than 7/16" of breech plug depth for the vent hole to be positioned forward of the plug face. Of course, you can position the lock with the fence forward of the end of the bbl but but this is a "low rent" solution, in my opinion. The old rifles were not constructed in this manner.

Once I have the bbl cut so the thread depth for the breech plug is correct to match the fence to center of pan measurement of my lock, I run a proper sized machine screw into the bbl so it fetches up tightly with the end of the threaded mortise. I cut off the end of the machine screw and file the two vertical sides flat of the part of the plug that protrudes from the end of the bbl. I then tack weld a tang to the plug so it fetches up tight to the top flat of the bbl. Then pull the plug, finish welding up the tang, and file out the tang/plug so everything is proper. You now have a breech plug that matches your lock's fence to center of pan dimension.

I have an old long rifle that has been in my family for many generations. The plug depth is less than 3/8" and the threads are course. I shot that rifle for at least 40 years now and never had a bit of trouble. In my opinion today's bbls that are prethreaded for the breech plug are threaded too deep and store bought plugs are too long to properly fit a Siler type lock. The only locks that I've been able to use without modifying the plug's thread depth are Chamber's Colonial Virgina or the Ketland locks as the fence/pan dimensions are more generous. I just measured a Chamber's Colonial Virginia lock and the fence to center of pan distance is 11/16". Consequently, a deeper plug will work OK with this lock.

 

[fho]

The gun that I want to build is a flintlock Lehigh style. The barrel is a 13/16 x 36-45 caliber. To me this is a thin barel, so I want to make it into a flint,as with the vent it releases pressure through the vent.

I shortened the breech plug from 9/16 in. to 1/2 in. I was told to do this so the lock will be inletted in the right place. I was also told that the vent hole should be 1/8 in. ahead of the breech plug.

I want to use the biggest vent that I can use, so I bought a 5/16 x 32 (lighting vent) from Track of the Wolf.

I think that I will take the works off of the flintlock and then lay it on the stock to see just where I can place the pan in relation to the vent hole. I an going to put the vent in the barrel after I inlet the lock. The flintlock that I am using is a Siler put togather by Locks & Stuff.

 

[Zonie]

I was also told that the vent hole should be 1/8 in. ahead of the breech plug.

I want to use the biggest vent that I can use, so I bought a 5/16 x 32 (lighting vent) from Track of the Wolf.
_________________________________________

Well, if you put the center of the 5/16 diameter vent 1/8 in front of the breech plug face, you will end up in cutting into the breech plug face 1/32 of an inch. Not good.

Either you have to install the vent 5/32 ahead of the breech plug face, or buy yourself a 1/4 inch thread vent liner.

Also, IMO, the 5/16 inch vent liner is too large for the 13/16 barrel you have.
The width of the flats on a 13/16 barrel calculates to be .336. The 5/16 dia vent liner is .312 in size. That only leaves .0245 of flat remaining and you have to divide this in half to find out how much material a perfectly centered vent would leave on the barrel flat. That would be .0123.
If you need to position the plug over .012 up or down from dead center the threads will end up breaking out into the adjacent barrel flat.

I would strongly suggest that you order a 1/4 diameter vent liner. The White Lightning is available in that thread size from Suzie at the MBS.

Zonie

 

[fho]

I put a line on the barrel 3/16 ahead of the breech plug. The back part of the pan is 1/4 ahead of the back end of the barrel. Is this O.K.?

I also have to make a drum for a 3/4 wide, 30 caliber barrel. I am thinking of making it out of 304 stainless or 4150. Which is best? I know that 304 stainless is hard to work (mean stuff). The thread that goes in the barrel, I was going the a 7mm. thread, but don't know if I should use a .75mm or a 1mm. pitch thread. On a drum there is very little wall thickness between the hole and the bottom of the threads. The .75mm pitch is a shallower thread than the 1mm. pitch and I would have more wall thickness. What do you think?

Thank you
Olie

 

[Zonie]

Seems a bit strange that your using metric threads, but if given a choice, I would go with the fine pitch threads. Not only is the root or minor diameter larger, but there is more material surface area interfacing between the male and female therads. This tends to reduce the leakage thru the threads.

I would make the drum out of the 4150 material for several reasons.
First, being steel, it will blue or brown while the 300 series stainless will not.
Second, even in its annealed state, the 4150 has higher tensile and yield strengths than the 304 stainless. If you heat treat the 4150, tensile strengths of as much as 301,000 psi can be reached as compared with the 304's 84,000 psi. As a side note, either material is better than the low carbon steel used for muzzleloading percussion barrels and drums.

The machinability index for both materials are the same, but IMO, because the 4150 has the potential for a much higher tensile/yield strength than the 304 it is very important not to let a cutter dwell in one spot. Dwelling of course will work harden either material.

 

[fho]

The reason I use metric threads sometimes is that they are about halfway between 1/16's. 7 mm = .276 in. which is about halfway between 1/4 and 5/16.

What about the fence of a flintlock being 1/4 in. ahead of the breech end of the barrel?

Thank you
Olie

 

[Zonie]

Olie: The fence being 1/4 inch ahead of the rear of the barrel is an issue that only you can decide on. It's your gun.

As some have said, "Since the fence is typically aligned with the breech end of the bbl..." that would indicate your gun might be in error.

Let me say though, I am looking at ROC and I find a number of guns shown which have the fence located from flush with the rear of the barrel to being located (by eyeball reckoning) up to 5/16 ahead of the end of the barrel.
As your building a Lehigh, here is my eyeball measurement of some of the ROC Lehighs:
83j: flush
84h: 3/16
85i: 1/8
86j: 1/8
87i: 1/8
88d: 1/8
89f: 1/8

Do these eyeball estimates mean 1/4 inch is wrong? I personally do not think so. It means your gun is not the same as the ones in the pictures.
Is 1/8 inch more than most of the pictures show bad? To a very few, yes. To the majority (IMO) it is acceptable. To the majority of the people who look at it it would make no difference at all.
I believe that 99.8+ percent of the people who look at your gun will have absolutly no idea as to whether it is "right" or "wrong".

Perhaps they were just being kind, but the fences on all of the Pennsylvania Rifles I've built are around 1/4 inch ahead of the back of the barrel and I have yet to have anyone point that out to me.

Zonie