Breechplugs

[northmn]

I have been using 3 different types of breech plugs lately and will share some of my experiences.  The first is a sort of nock type breech I used when I used a modern shotgun barrel for a fowler.  To maintain length I inserted a long breech plug of over 1 inch to maintain barrel length.  I counter drilled about a 1/2 inch hole to get a normal length.  It needs a minimum of about 50 grains of powder to fill the breech.  As it is a 12 bore that is not much of an issue.  It is also a real PITA to clean.  I have also cupped a couple of 3/4 inch breeches about 1/4 inch to get more of a fit which at one time I thought would permit more of an original lock placement (seen some pictures that differ).  No real problem except that you again have different cleaning issues.  They do permit a lock to be seated further back, especially if you use a vent insert.  Pletcher mentioned that they may have slightly slower ignition.  For my 25 I just cut the breech back a little bit and used a square fit.  Easier to clean.  Probably will go with that if I want a shorter breechplug system.  Older guns I have thought only used breeches about 1/2 inch deep and Coleraine had .55 plugs.  I really question if "square" plugs are needed.

DP

[Acer Saccharum]

I tried this style breech, and could not tell if it was any faster firing. It did run clean, never had any issues with plugging. It is definitely harder to clean after shooting, requiring a patch wrapped around a brush to get down in the recess.



This is how I like to breech and install a liner. Most barrels as they come need a bit of fitting to get the plug sealed on the bore. When the bore is near tap size, there isn't much fitting that can be done. This isn't required for safety, but for easier cleaning. No undercuts or exposed threads to retain $#@*.

[dave m.1]

    after building my first rifle with a 50 cal rice barrel I have a small undercut around the breech plug.when cleaning I can never seem to get the gunk out of that space,never thought to use a patch over the brush.I will try that.I do love the barrel it shoots great at fifty yards from a bench most shots will be touching,except when my tired old eyes act up.(which is often)

[Acer Saccharum]

Get some Tow. Wad it up and shove it down the bore, skoodge it all around, pull it out with a worm. The tow pulls a lot of stuff out of the nooks and crannies.

Can be gotten from the "Silver Shuttle" by the pound. Get the coarse stuff, with bits of stalk, scrubs real good. A lot cheaper, since it's too coarse to make linen from.

[FG1]

Dont really know how this applies to barrel breaching but I remember back when an apprentice in industrial pipefitting we were taught to have the same amount of threaded shank for thread engagement as the diameter of bolt . Now I know that some nuts are shallower than that but still pretty close . Would the same hold true to breech threads? I have always trimmed just what was needed to get a good breech seal . But if trimming barrel and plug to get the fence parallel with breech of barrel is a non issue that would be more eye appealing.   

[D. Taylor Sapergia]

Very few original rifles have the fence line up with the end of the barrel.  It is not important.  One half inch of thread journal is all you need for any of the plugs that go into muzzle loader barrels.
I unbreeched my double 14 gauge Staudenmayer barrels, and the journals were only 3/8" long, and just slightly larger than the bore.  There was no shoulder in the barrel for the plugs to come up hard against. 
After at least two hundred years, the threads on the plugs and those in the barrels were bright and shiny with absolutely no oxidation.

[Joe Stein]

I don't have anything to add that hasn't already been said, but here is a link to everything you probably would want to know about bolts, nuts, threads and their properties

http://www.boltscience.com/pages/screw1.htm

-Joe

[Dave Dolliver]

The old rule for having thread length equal to the diameter of the bolt was to come close to developing the strength of the bolt in the theaded connection.

In a breech blug we are not using the plug as a bolt under tension load but as a PLUG to resist a black powder chamber pressure that is less than half the tension allowable of the bolt so 1/2" of thread length should be plenty.

Green Mtn barrels come with a threaded breech length about the length of the thread diameter-- modern criteria for thread length.  So do most of the breech plugs you can buy.  I feel the gun looks
better if I shorten the barrel and plug to have about 1/2" of thread but that's just my opinion not something that's absolutely neccessary or correct.

Dave Dolliver

[FG1]

Very few original rifles have the fence line up with the end of the barrel.  It is not important.  One half inch of thread journal is all you need for any of the plugs that go into muzzle loader barrels.
I unbreeched my double 14 gauge Staudenmayer barrels, and the journals were only 3/8" long, and just slightly larger than the bore.  There was no shoulder in the barrel for the plugs to come up hard against. 
After at least two hundred years, the threads on the plugs and those in the barrels were bright and shiny with absolutely no oxidation.

Daryl, I have a set of Belgian 11 ga. ? (18.4) that are threaded 3/4-16 and looks like no shoulder abuttment either . The threads just run out at bore . Ive been contemplating iether going with a special 13/16" tap or going up to 7/8 x14 in order to get a seal .

[Dphariss]

In large bores with thin walls there is little choice but to tap the bore and Taylor is correct in his assessment.
But old technology and modern technology are often somewhat different so then we must ask.
How tight is the thread fit on these originals? Close thread tolerance and/or are the threads in the barrel being filled completely by the plug is different than how some moderns are breeched.
This is an original breech from a kentucky with a well rusted bore (I can no longer check the thread fit but I still have the plug). But the threads are largely rust free.


I have pulled a number of moderns that had fouling back 2 or more threads due to the threads being open to the powder gases from having a notched breech face. Did not corrode but it as powder fouling just the same. Had it been one of the corrosive substitutes the plug probably would not had come out or worse teh rust could have done major damage at the point of greatest strain when firing.
I just rebreeched a barrel that was threaded 4 threads deeper than the plug in a a modern 56 caliber smooth bore with a 5/8 plug. It not only trapped fouling it would catch a patch on a jag. Breeched by the barrel maker I am sure. I rebored deeper and fitted a 11/16 plug to a shoulder. The wall thickness was too thin for a 3/4 plug.

This is a fouling trap that is the result of someone, the barrel maker since they sell breeched barrels, who really should know better but was apparently too lazy to do it right. This was "good enough" it would seem. It would never blow out true but this is not the only test of proper breeching.

This is the bore scope view you can see down into the threads in the rifling grooves.


This is when it was first pulled from the barrel.




The rifle was not properly cleaned but even a thorough cleaning would have left fouling in the "trap".
When this becomes contaminated with oil or water it can cause contamination of the powder charge since its very difficult to "dry the oil" since its in a hidden area.
This is the plug after cleaning the fouling off it. This makes the trap pretty obvious.

The vent installation was done by the gunstocker and was not well done either.


So while the breeching of old guns may not be shouldered its also not like this breech. Which was very similar to the 56 smooth barrel previously mentioned except this is a 5/8 plug in a 50 cal rifle barrel.

This barrel is a 54 breeched to a shoulder with a 3/4 plug, the vent is right at the face of the breech but there is no exposed threads in either the liner or the plug and no oil/solvent/fouling trap.




This is a 58 caliber I cut 8" at the breech for a rebarrel  then bored and tapped for 3/4 16. Plug was fit to the shoulder.


Dan

[Blacksmoke]

Gentlemen:  The topic of breech plugs is one that deserves as much attention as possible because of it's nature of safety!   If you have ever had a barrel fail on the firing line or have been standing next to the person who has, you will know what I mean.  In my opinion "more is better" threads that is.  And yes there should NOT be a "trap" where fouling can collect.  Those of you who are trusting the barrel makers to breech a barrel for need to unscrew the breech plug and check the inside shoulder to make sure that the plug is seated properly!  Hats off to Dan who obviously does this!  The following pictures will illustrate how I do my breeching.  This is not a new system - and it's one of the strongest breeching systems ever used!    Also the way I do it will provide you with a simple way to install the lock with it's fence against the breech shoulder where it belongs.  Now I know some old originals have their lock somewhat forward but from an as thetic point of view it looks better when the lock is back against the breech.    Just because an "old timer" did it doesn't make it correct or safe!                                                            

[flehto]

There really seems to be 3 issues asre the various types of breech plugs and their threaded lengths. Safety, sealing off the gases and ease of cleaning.  Judging from the short threaded lengths on the "old guns" using coarse threads and having survived many years w/o incident, are we "moderns"  over doing the safety factor? When a modern bbl bursts due to whatever cause and from the  pics I've seen,  the breechplug is still in the bbl and really was unaffected. The bbl manufacturers due to liability concerns in this "age of lawsuits" make the bbls and breechplugs according to  accepted"engineering standards"  seeing there are no other guidelines that would stand up in court. The force exerted on the threads of a properly seated breechplug is determined by the area of the bore times the pressure and  this force doesn't come anywhere close to the yield point of the threads even when overloaded and the bbl bursts. It seems the "old timers" knew this but due to an "over-engineering" mindset and  lawsuits, we've ended up w/ a minimum of 1/2" of fine threads.  The other 2 issues I'll leave to the more expeienced shooters....Fred

[Roger Fisher]

Get some Tow. Wad it up and shove it down the bore, skoodge it all around, pull it out with a worm. The tow pulls a lot of stuff out of the nooks and crannies.

Can be gotten from the "Silver Shuttle" by the pound. Get the coarse stuff, with bits of stalk, scrubs real good. A lot cheaper, since it's too coarse to make linen from.

This has been gone over several times before. I run a sloppy wet patch down to the breech or plug off the vent or nipple and pour a tablespoon or so water down and leave her sit while I mess around with my other chores or 10 min or such.  I then go in with a seperate range rod with a worm attached and patch doubled up on it. And then wipe the plug face.  By that time the fouling is soft as sn--! 

I polish the face of the plug when abuilding the beasty and do not counterbore the thingee. 

Whatever you do be sure you get the fouling out since it turns into concrete with all the headaches that it creates. 

btw - I file a cross across the cupped jag face and go in bare at times during a shoot, press her against the polished plug face give it a minor twist and the jag comes out packed full of fouling.  Good way to stop it from building up and causing more problems be they ignition or cleaning...

[Dphariss]

Gentlemen:  The topic of breech plugs is one that deserves as much attention as possible because of it's nature of safety!   If you have ever had a barrel fail on the firing line or have been standing next to the person who has, you will know what I mean.  In my opinion "more is better" threads that is.  And yes there should NOT be a "trap" where fouling can collect.  Those of you who are trusting the barrel makers to breech a barrel for need to unscrew the breech plug and check the inside shoulder to make sure that the plug is seated properly!  Hats off to Dan who obviously does this!  The following pictures will illustrate how I do my breeching.  This is not a new system - and it's one of the strongest breeching systems ever used!    Also the way I do it will provide you with a simple way to install the lock with it's fence against the breech shoulder where it belongs.  Now I know some old originals have their lock somewhat forward but from an as thetic point of view it looks better when the lock is back against the breech.    Just because an "old timer" did it doesn't make it correct or safe! 

Thanks Hugh.

To expand somewhat...
I have used virtually the same system at times with minor variations and it works very well and I like it. It solves many problems and is stronger than a vent drilled into the barrel in front of the breech


A similar breech is illustrated in WW Greener's "The Gun and its Development" IIRC.
The cup or cavity in the plug should, as Hugh's drawing shows, be slightly under bore or even smaller depending on the diameter of the plug. I have patent breeches in the swivel breech with a cavity just under 3/8".
Making it the same size as the bore may allow a ball with no powder to be seated deep enough to block the vent and make pulling the ball necessary.
I greatly prefer buying unbreeched barrels. I also prefer the locks fence at the breech end of the barrel. Makes for a cleaner look with no little sliver of wood to break off behind the fence.
This is the exterior of the barrel that has the liner right at the breech face. Its possible to see the powder in the vent liner as well.


This is a plug from a ML made by a big name in firearms since the 1800s. Not the rust at the face since it has a fouling trap at the face of the breech. Shooting these with BP just makes them hard to clean. Shooting them with one of the corossive substitutes can result in crawdad holes being eaten into the breech at the thinnest point. I have some photos of this from Mad Monk some place. The corrosive elements seemingly get a good start then eat their way out forming a tunnel.


Back in the day there were a lot of poorly breeched barrels, bad iron barrels etc and people got hurt and killed. While the original breech shown survived in service I don't like it and posted the photo just to show that the threads were not subjected to fouling as it was fit properly and/or had low tolerance between the plug threads and the tapped barrel. Modern taps and dies usually have .005"-.008 combined tolerance (if not a little more).
Even with supposedly superior modern metals nipples blow out, drums break off, vents can blow out or gas cut the threads in flint guns. Often its POOR WORKMANSHIP,  either from apathy, ignorance or economics. One of the major makers used to leave a gap at the end of the threads then installed the breeches by machine at high torque, whatever was needed to index to the top flat. So tight that attempting to remove the breech would sometimes BREAK THEM OFF.  But it required no labor to fit the plug. Just lube it and screw it in. That it greatly stretched the thinnest part of the patent breech was of no concern and I don't know of any failing at that point in service I.E. the breech blowing off when it was fired.
This is the face of the breech that was installed in the 58 caliber barrel pictured previously. It is possible to see the lands and grooves imprinted on the blue Magic Marker applied to the face. Perfect seal. I then machine the tang. This plug is made from GB quality chrome-moly barrel steel the barrel is a Green Mountain.

In this case I had a lot of thread length so I rebated the threads. But in this case since the bore is sealed there is no fouling trap.

This is the face of a GM 50 caliber SB barrel with a 5/8 plug its too is sealed.


Yes I do this with a lathe and a mill when making the plug from stock.
BUT its not that difficult for anyone to do it that has a file, a vise, a magic marker and the knowledge of how its supposed to look. I used to do it this way. Some wet or dry paper to polish the breech face is nice too. Its not THAT difficult to do it right but it takes time and most barrel makers cannot take this much time and still sell to the mass market since they can put $100+ in shop time just in the breeching.

Dan

[northmn]

For strength you cannot beat systems like Blacksmoke and Dan suggest.  As stated I used one to breech a modern shotgun barrel.  I have to clean the thing with a modern shotgun slotted jag as the normal 12 jag does not fit in the counter bore.  I still have to be watchful as that counter bore is something of a rust trap.  But I also consider bore diameter vs breech diameter as a factor.  Consider that a 50 cal only has a 50 cal area of pressure against say a 5/8 or 3/4 inch breech face.  Consider a 58 against the same breech plug.  Due to the factors of area being increased by the square of the radius the 58 has a area of about .26 square inches as compared to the 50 at about .2 square inches.  A little more thread depth may make more sense on a large bore, but then again if well seated enough is enough.

DP

[FL-Flintlock]

If one looks at the mechanics of fastener loading of a 7/8"-9 capscrew, the first thread on the compression side takes approximately 34% of the total load, subsequent threads #2-23%, #3-16%, #4-11%, #5-9% and #6-7%.  I don't recall the loading percentages per-thread on UNF fasteners but the loading is similarly disproportional with the first 3-4 threads taking about 75% of the total load as with the previous example.  Any disruption of the threads completely changes loading characteristics resulting in a considerable strength reduction as has been a major problem with application of nylock capscrews where the nylon plug disrupting the threads results in approximately 50% reduction in the yield strength of the threaded connection.  The accepted rule of thumb is for the thread engagement length to be equal to one diameter plus 12% for tolerance, any additional thread engagement has negligible effects on connection strength. 

I have seen a statement made counterboring the breech to the effect of, "The counterbore allows the pressure generated by the powder to make the threads engage harder."  All one need do is apply some basic logic to understand that even a stiff load under a heavy projectile is only going to produce about 30 ksi which roughly half the strength of the steel in a solid plug.  Furthermore, as a counterbored plug expands from the pressure generated by the propulsion charge, this effectively changes the profile of the thread engagement surface area which increases the amount of stress on the threads and therefore reduces the nominal strength of the connection.

Pressure is equal at all points within a containment, the plug sees no higher/lower pressure than the barrel walls or the vent/nipple.  If the plug is properly faced to the bore as Dan shows, the surface area is equal to the bore area plus the groove area if the bore is rifled, the diameter of the plug is thus irrelevant to the applied pressure surface area.  Whereas if one uses either a 5/8" or 3/4 or 7/8" plug in a 0.50" bore, the pressure applied to the plug face will remain the same provided the plug is properly installed - the only change one would see is the actual pounds per square inch of loading applied to the individual threads as the larger the mean diameter of the plug, the more bearing surface each thread has, however, the percentage of loading per thread remains the same.

[Robby]

I'm installing a plug for a hooked breech on a 1-1/8, .69 cal bbl. Acer's illustration on the top show's it pretty clear, except the hook. I will be using a white lightning liner. The bore of the plug is 5/16" diameter, and I was thinking of opening that bore to 3/8" to have more powder closer to the point of ignition. It seems like a good idea to me, but, I guess I'd like to know if I am missing something, or creating a problem.
Robby

[Dphariss]

I'm installing a plug for a hooked breech on a 1-1/8, .69 cal bbl. Acer's illustration on the top show's it pretty clear, except the hook. I will be using a white lightning liner. The bore of the plug is 5/16" diameter, and I was thinking of opening that bore to 3/8" to have more powder closer to the point of ignition. It seems like a good idea to me, but, I guess I'd like to know if I am missing something, or creating a problem.
Robby

5/16 is too small.
I would open it to 3/8 or maybe 7/16 if a 3/4 plug with NO rebate at the breech end of the threads.
You will still need a 410 or 20 ga shogun mop to wipe/oil the cavity in the breech.
Or make a stepped jag.
The breech is made for the smallest possible bore size.
These were made for 50 caliber barrels. 3/8 cavity.


This is as thin as the cavity could be really and the material is GB quality 4140.
Dan

[Dphariss]

PS

Be careful not to bore too deep and make the breech end too thin.
Measure and think.


Dan

[Acer Saccharum]

I feel like I made my powder chamber way too deep, first one of my illustrations. But it did put the liner in the breechplug, completely independent of the barrel.

[Blacksmoke]

Robby - I concur with Dan - 5/16" is too narrow!  The counter bore in the plug should also be tapered or cupped as illustrated in my drawing.  This is done by employing the use of a "rotary file" from Nicholson or a milling bit of a similar description.  Try to stay away from parallel sides and sharp corners as these provide weak points for possible breech failure - these are also places where fouling can accumulate. When the counter bore is finally milled out I will polish the inside surface with a piece of fine Emory paper wrapped on a small mandrel.  This will aid in the cleaning process.    Hope this helps.  Hugh

[Robby]

Thanks Dan. I plan to go no deeper than the existing chamber. Hugh, This makes real sense to me, that all the break over points would be either coped or rounded over Depending on inside or outside, I believe this would help facilitate the flow of stresses.
Robby