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Breech Plug
- Thread starter crockett
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Crockett,
It is probably better to have the breechplug installed. Most barrel makers do this as a matter of fact and it is included in the price of the barrel.
If you want to try installing your own it is not that hard, just time consuming. Tanstaafl who writes in on this board wrote a tutorial on installing your own breechplug. Maybe he will be able to tell you where to find the tutorial and I won't need to write a big long message on how to do it.
Randy Hedden
It is probably better to have the breechplug installed. Most barrel makers do this as a matter of fact and it is included in the price of the barrel.
If you want to try installing your own it is not that hard, just time consuming. Tanstaafl who writes in on this board wrote a tutorial on installing your own breechplug. Maybe he will be able to tell you where to find the tutorial and I won't need to write a big long message on how to do it.
Randy Hedden
CrackStock
69 Cal.
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It is important to get the plug to seal inside at the same time as it nests along the top flat. You should not have a gap in there to keep fouling in this area. It takes careful work to achieve this. I would check any gun that I paid for this to be done since I would suspect that they might have simply cut it short for easy money.
CS
CS
Going a little further with the description of what is needed; you just have to get four different things to happen at the same time.
The face of the plug must stop on the shoulder where the bore stops and the threads start.
The front of the tang must be tight against the rear of the barrel.
The tang flat must align with the barrel flat.
All of these things must happen at the same time the threads start to strongly resist further tightening of the plug.
This, for me, is a time consuming task when my only metal working tool is a file.
I vote for paying the $20 and having the job done for you. The only catch here is there are some places who do a half ass job of it and consider their job done while the plug is still standing clear of the bore shoulder.
zonie
The face of the plug must stop on the shoulder where the bore stops and the threads start.
The front of the tang must be tight against the rear of the barrel.
The tang flat must align with the barrel flat.
All of these things must happen at the same time the threads start to strongly resist further tightening of the plug.
This, for me, is a time consuming task when my only metal working tool is a file.
I vote for paying the $20 and having the job done for you. The only catch here is there are some places who do a half ass job of it and consider their job done while the plug is still standing clear of the bore shoulder.
zonie
FWIW, I will post it here Hardog.
A Method for Fitting Breech Plugs
By Roland Chambers
This is the way I file fit breech plugs , and offer it only as that, nothing more.
I would like to preface the following by saying files are nothing less than hand operated lathe and milling tools. If anyone thinks that filing is just put it to the metal and start stroking hard, I advise you to re-think that concept carefully before starting to fit breech plugs, or any filed metal work requiring a degree of precision. To file, and file correctly, takes practice, practice and more practice until skill approaches art. I have not reached the latter proficiency after several decades, and have been proven wrong more than once so far as having skill.
If your unmarked barrel is from round stock where the flats were machined on center after drilling, reaming and rifling, you can almost always go to the nearest flat when fitting bolster. If octagon stock was drilled, reamed and rifled, there is a good chance you will have to check carefully for any run out, that to be indexed in the vertical when fitting tang bolster. This may require filing the rear face of barrel. Otherwise, you may have some rather extreme looking front and rear sights drifted to the left & right to get on target.
When fitting, I always hope for the threaded length of breech plug to be more (.750") than depth barrel is threaded to the shoulder, (.625") I know then it will be a quick and easy job. I start by checking rear barrel face for square, check internal shoulder (sometimes a knife edge needs to be removed) and clean up milled tang bolster face edges. Then with a depth gauge or veneer caliper check the depth of internal shoulder from rear of barrel face, and length of breech plug from bolster to face. This tells one quickly which to reduce, the breech plug, or the rear of the barrel. If the breech plug is longer, I run it in by hand until I feel it start to bottom out solid against the shoulder, I then use a inside veneer caliper measurement to obtain a more accurate reading of how much material to initially remove.
I then use masking tape to mark off material I want to initially remove, making sure circumference of threads is taped evenly so at least .025" less material will be removed than desired, this will allow for final fitting. I then plumb breech plug true vertical in a vise and with a coarse bastard file I file level as possible across breech plug face until it is scored evenly and completely, stop, that, and no more. I then again level as possible, file breech plug face 90 degrees to first cut, this will initially produce a cross hatch effect, I only file until cross hatch is eliminated and return 90 degrees to first cut position. By repeating this filing process correctly, I find I can quickly and evenly reduce that material decided upon.
I then remove masking tape and use a small machinist's square to check face of breech plug for true. If uneven, remove high spots until it is true. I then take a small mill file and ever so lightly chamfer breech plug face circumference to remove any jagged knife edges sticking out. (not fun to run those steel slivers into a pinky and then break one off deep below the skin surface, I am not a fan of Exacto blade self surgery)
I then again run breech plug in by hand and obtain a reading. If considerable material remains to remove, I repeat the cross hatch filing, but checking all steps more frequently until close. If close, I will then use a mill file on breech plug face and start using Prussian blue transfer paste on internal shoulder, I use a wrench to tighten breech plug lightly to obtain a true impression. All the while closely monitoring bolster faces for barrel contact, so as to bring breech plug, and bolster to barrel final fits simultaneously.
When it was the threaded length of breech plug I had to reduce, I have seldom ever, had to remove material from rear of a unmarked center machined flats barrel face, when I did, it was almost always operator error, for I goofed up and had to go for another flat. ( this mistake can be a real bummer on those barrels with run out, after just getting it so close to right)
On final tightening of breech plug, it is well to remember we are dealing with soft steel here, there is tight, and then there is "TIGHT". If one gets western and over torques, a considerable pre-load can be imparted to those threads. Now I don't know about others, but I prefer that powder charges alone imparts those big loads to the breech plug threads, not have every shot become a proof load.
( I will throw this tid bit in here about hack saws. A quantum leap in hack saw control for precision cuts can be as simple as reversing the blade for pull, rather than push strokes. More than one has been pleasantly surprised when they go from herding cats to leading that blade exactly where they want it.)
This article is Copyright 2003 by Roland Chambers
A Method for Fitting Breech Plugs
By Roland Chambers
This is the way I file fit breech plugs , and offer it only as that, nothing more.
I would like to preface the following by saying files are nothing less than hand operated lathe and milling tools. If anyone thinks that filing is just put it to the metal and start stroking hard, I advise you to re-think that concept carefully before starting to fit breech plugs, or any filed metal work requiring a degree of precision. To file, and file correctly, takes practice, practice and more practice until skill approaches art. I have not reached the latter proficiency after several decades, and have been proven wrong more than once so far as having skill.
If your unmarked barrel is from round stock where the flats were machined on center after drilling, reaming and rifling, you can almost always go to the nearest flat when fitting bolster. If octagon stock was drilled, reamed and rifled, there is a good chance you will have to check carefully for any run out, that to be indexed in the vertical when fitting tang bolster. This may require filing the rear face of barrel. Otherwise, you may have some rather extreme looking front and rear sights drifted to the left & right to get on target.
When fitting, I always hope for the threaded length of breech plug to be more (.750") than depth barrel is threaded to the shoulder, (.625") I know then it will be a quick and easy job. I start by checking rear barrel face for square, check internal shoulder (sometimes a knife edge needs to be removed) and clean up milled tang bolster face edges. Then with a depth gauge or veneer caliper check the depth of internal shoulder from rear of barrel face, and length of breech plug from bolster to face. This tells one quickly which to reduce, the breech plug, or the rear of the barrel. If the breech plug is longer, I run it in by hand until I feel it start to bottom out solid against the shoulder, I then use a inside veneer caliper measurement to obtain a more accurate reading of how much material to initially remove.
I then use masking tape to mark off material I want to initially remove, making sure circumference of threads is taped evenly so at least .025" less material will be removed than desired, this will allow for final fitting. I then plumb breech plug true vertical in a vise and with a coarse bastard file I file level as possible across breech plug face until it is scored evenly and completely, stop, that, and no more. I then again level as possible, file breech plug face 90 degrees to first cut, this will initially produce a cross hatch effect, I only file until cross hatch is eliminated and return 90 degrees to first cut position. By repeating this filing process correctly, I find I can quickly and evenly reduce that material decided upon.
I then remove masking tape and use a small machinist's square to check face of breech plug for true. If uneven, remove high spots until it is true. I then take a small mill file and ever so lightly chamfer breech plug face circumference to remove any jagged knife edges sticking out. (not fun to run those steel slivers into a pinky and then break one off deep below the skin surface, I am not a fan of Exacto blade self surgery)
I then again run breech plug in by hand and obtain a reading. If considerable material remains to remove, I repeat the cross hatch filing, but checking all steps more frequently until close. If close, I will then use a mill file on breech plug face and start using Prussian blue transfer paste on internal shoulder, I use a wrench to tighten breech plug lightly to obtain a true impression. All the while closely monitoring bolster faces for barrel contact, so as to bring breech plug, and bolster to barrel final fits simultaneously.
When it was the threaded length of breech plug I had to reduce, I have seldom ever, had to remove material from rear of a unmarked center machined flats barrel face, when I did, it was almost always operator error, for I goofed up and had to go for another flat. ( this mistake can be a real bummer on those barrels with run out, after just getting it so close to right)
On final tightening of breech plug, it is well to remember we are dealing with soft steel here, there is tight, and then there is "TIGHT". If one gets western and over torques, a considerable pre-load can be imparted to those threads. Now I don't know about others, but I prefer that powder charges alone imparts those big loads to the breech plug threads, not have every shot become a proof load.
( I will throw this tid bit in here about hack saws. A quantum leap in hack saw control for precision cuts can be as simple as reversing the blade for pull, rather than push strokes. More than one has been pleasantly surprised when they go from herding cats to leading that blade exactly where they want it.)
This article is Copyright 2003 by Roland Chambers
TANSTAAFL makes many a very valid point.
Threads only have so much load that they can impart or resist. If the threads strength is used up in tightening the plug then what is left to take the pressure when the gun is fired?
zonie
Threads only have so much load that they can impart or resist. If the threads strength is used up in tightening the plug then what is left to take the pressure when the gun is fired?
zonie
k.jacobfrost
40 Cal.
I'm slowly working on making a few pistols in .50 cal. The barels I am going to use are plain round smoothbore and are 1" od, I am concidering using one of the plugs from this site, I'm liking the flared tang plug. BreachPlugs
Now for the questions. What size should I use. And seing that I will be drilling the threds myself, do I just cut the threds into the breach or does the plug need to be bigger then the bore?
Also scence you mentioned it, how tight should the breach plug be?
Now for the questions. What size should I use. And seing that I will be drilling the threds myself, do I just cut the threds into the breach or does the plug need to be bigger then the bore?
Also scence you mentioned it, how tight should the breach plug be?
If me, I would go for a 5/8" (.625") BP for .50 cal in a 1' O.D. round bbl. This would still give one 3/16" (.1875") of bbl wall thickness in threaded area.
One could use a 9/16" (.5625") BP, but in a .50 caliber, would only give a 1/32" (.03125") shoulder for the BP to mate up.
As to how tight is tight? I have never torque tested, I just try to make sure I don't over/under torque. After decades of pulling wrenches for a living, I have seen more problems arise from over torquing fasteners, than from under.
One could use a 9/16" (.5625") BP, but in a .50 caliber, would only give a 1/32" (.03125") shoulder for the BP to mate up.
As to how tight is tight? I have never torque tested, I just try to make sure I don't over/under torque. After decades of pulling wrenches for a living, I have seen more problems arise from over torquing fasteners, than from under.
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Zonie and tanstaafl are right- additionally, i'd figure it out for myself because (a) that's the way my head works, (b) i've had barrels that came with the breechplug already installed and when i went to remove the plug and replace it with a different shaped one, i couldn't get it out, which means (imo) that it was overtorqued.
good luck- go slow.
msw
good luck- go slow.
msw
k.jacobfrost
40 Cal.
Thanks. But what does "bbl" translate to?
The only experience (if can call it that) with bp has been what I have learned or read on this forum. So I can guarantee that I will be asking a lot of questions during my upcoming project. I will post pictures of what I am planning on making just as soon as I can get my computer to start talking to my camera again. :cursing:
The only experience (if can call it that) with bp has been what I have learned or read on this forum. So I can guarantee that I will be asking a lot of questions during my upcoming project. I will post pictures of what I am planning on making just as soon as I can get my computer to start talking to my camera again. :cursing:
CrackStock said:
Crackstock and Zonie,
Unfortunately TANSTAAFL and I have both learned that two of the well known and praised barrel companies do not even worry about getting that internal seal that you both are talking about. I would suggest to anyone that is purchasing a barrel that has the breech plug installed should pull the breech plug and check for the internal seal. I know TANSTAAFL and I have both reworked the breeching on these barrels because they have no internal seal what-so-ever.
Randy Hedden
Maybe one reason the hooked breech came into use is that the hook part can be left in the round until the plug is fitted, then just cut the hook where it needs to be. No multiple fitting to do. Just run the end of the breech into the shoulder and cut the part that's sticking out.
That would almost make up for the extra work of making the false breech that it hooks into, besides making the barrel easier to get out.
That would almost make up for the extra work of making the false breech that it hooks into, besides making the barrel easier to get out.
CrackStock
69 Cal.
- Joined
- Dec 23, 2004
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I have been percolating on this for years. I wonder how much the threads are actually accomplishing. It is not as if this were a pipe bomb where the threads were containing the full force of a powder charge without string support. Rather, the breach is butted up to the stock -- in many cases bedded to perfect the support.
I would be interested in comments from you all on this.
CS
Without giving the formulas I used to calculate it, for a barrel and breech plug made out of material with a tensile strength of 64,000 pounds and threaded with a 5/8-18 thread it should withstand a force of 16637.3 pounds.
If a .50 caliber gun shooting a conical with a hot powder charge is fired in our psudo gun, it may generate a breech pressure over 27,000 PSI, but lets use 23,000 PSI.
This pressure is acting on not only the bullet, but also on the breech plug.
With a 5/8-18 threaded plug it has a face area of .307 square inches. That times 23,000 says it is being subjected to a pressure load of 7056.3 pounds.
Subtracting the 7056.3 pounds from the 16637.3 pounds leaves 9581 pounds.
I don't have my torque/load charts any more but I have no doubts that less than 100 ft/lbs of torque on that thread will create over 9000 pounds of load. (in case you didn't know it, a 5 foot pound torque load on a 1/4 inch bolt will generate more than 1000 pounds of load).
So, if we torqued the breech plug to create 9000 pounds of load, and the powder charge created 7056 pounds of load we are at 16056 pounds of force acting on the threads.
If they are only good for 16637 pounds, that leaves a safety margin of 581 pounds which is 3.5 percent.
Normally, the desired safety factor when dealing with life/death conditions is at least 200 percent, usually 400 percent. In other words, the thing is unsafe for the load used in this case.
As for the support the wood would give the plug, it doesn't work that way.
When the threads fail, the next thing in line must resist the total force and IMO, no small piece of wood is going to withstand these kinds of loads.
Hope this helps. :grin:
zonie
If a .50 caliber gun shooting a conical with a hot powder charge is fired in our psudo gun, it may generate a breech pressure over 27,000 PSI, but lets use 23,000 PSI.
This pressure is acting on not only the bullet, but also on the breech plug.
With a 5/8-18 threaded plug it has a face area of .307 square inches. That times 23,000 says it is being subjected to a pressure load of 7056.3 pounds.
Subtracting the 7056.3 pounds from the 16637.3 pounds leaves 9581 pounds.
I don't have my torque/load charts any more but I have no doubts that less than 100 ft/lbs of torque on that thread will create over 9000 pounds of load. (in case you didn't know it, a 5 foot pound torque load on a 1/4 inch bolt will generate more than 1000 pounds of load).
So, if we torqued the breech plug to create 9000 pounds of load, and the powder charge created 7056 pounds of load we are at 16056 pounds of force acting on the threads.
If they are only good for 16637 pounds, that leaves a safety margin of 581 pounds which is 3.5 percent.
Normally, the desired safety factor when dealing with life/death conditions is at least 200 percent, usually 400 percent. In other words, the thing is unsafe for the load used in this case.
As for the support the wood would give the plug, it doesn't work that way.
When the threads fail, the next thing in line must resist the total force and IMO, no small piece of wood is going to withstand these kinds of loads.
Hope this helps. :grin:
zonie
I don't have my torque/load charts any more but I have no doubts that less than 100 ft/lbs of torque on that thread will create over 9000 pounds of load. (in case you didn't know it, a 5 foot pound torque load on a 1/4 inch bolt will generate more than 1000 pounds of load).
Good point Zonie. Some may not realize it, but using say, a 12" (one foot) crescent wrench, an average guy who puts his body weight into it, can readily impart 100 foot lbs of torque onto a fastener.
Good point Zonie. Some may not realize it, but using say, a 12" (one foot) crescent wrench, an average guy who puts his body weight into it, can readily impart 100 foot lbs of torque onto a fastener.
