should breech plug be water tight

[oldarcher]

I have been shooting and building BP rifles since 1974, and am constantly amazed that we do not have more shooters killed or seriously hurt. Remember you are putting a open ended pipe bomb next to your face and igniting it with the hope that the ball is in the bore more loosely than the plug or the drum or nipple is attached and it actually shoots out rather than exploding. As everyone who has responded has said, the plug must be tight.
Please do not misunderstand, I am not being a smart a$$, but if you actually question if the plug should be "water tight" you should question if you should be shooting BP Guns. I apologize in advance for offending you. Please find someone to teach you about the dangers of the guns you are shooting and listen to them.

[alacran]

Watertight really? How many of you put water in the barrel and leave it in there long enough to see if it is watertight? Who buys a Rice or Colerain beached barrel place water in it and leave it long enough to see if it is watertight?

[oldarcher]

I disassemble my rifles after shooting, or I use the flushing device that I purchased from TOW to clean my flint longrifles.
I clean my rifles with cool soapy water, and flush with clear water, blow the barrel out with high pressure air. I then wipe the bore with many clean patches, then with wd40 then clean patches, then light gun oil, then with clean patches.
I have never had a rust issue of any kind. Even a year later the patch is dirty but no rust. (my rifles rarely set longer than 2-3 months without being shot and cleaned). I am sure that I would notice water leaking through the breech plug, I really would not have to wait on water, the gas blow-by would certainly attract my attention.

[Turtle]

 Some people plug the touchhole and pour water in the barrel and let it sit a while to clean. Then they pour it out and repeat. This is where I have seen water leak past the breechplug. I don't do this unless I have been shooting blanks-which makes a nasty cleaning job.

[alacran]

I suppose that is the point I am trying to make Turtle.  If you don't have some sort of anti seize wether it  is teflon tape , locktite or some other such material, water will find its way through any imperfection of a metal mated surface.

[davec2]

I tried not to weigh in on this topic, but I just can't help making a couple of comments.

1.  First and foremost, Yes, a breech plug should be well fitted
2.  In my business (rocket engines) I routinely seal helium and hydrogen systems (MUCH more difficult to do than powder gasses) up to 10,000 psi and other types of gas systems up to 35,000 psi.  I think I am familiar with sealing high pressure, and often very hot, gasses (in excess of 5500 degrees F).  Anyone who thinks that even a well fitted, straight thread plug with an excellent interference fit on a well machined shoulder can seal hot gas at 10,000 psi is....well... not well informed.  No one worth his salt in my business would design a metallic seal like that with any hope of success. 
3.  The many breech plugs that don't appear to leak hot gas during shooting don't leak for a few very specific reasons.....

       a) The pressure pulse created in the bore during firing is very short...i.e. milliseconds....about 3.6 milliseconds for a 48 inch barrel ...and the pressure is dropping the
           whole time. 
       b) The threads themselves form what is often referred to as a "labyrinth seal"...i.e. every time the gas tries to go around a corner, or through a very restricted space, it
           drops in pressure.  The same as putting a restricting orifice in a gas line to choke down the flow rate.
       c) The first bit of powder fouling that gets driven into any leak path around the breech shoulder and first couple of threads forms a packing that enhances the "labyrinth"
           effectiveness.
       d) NO flintlock breech is water or gas tight....we all purposely drill a hole in the breech area that lets fire in and gas out.  Without a toothpick, they all leak water.
       e) Every time I fire my much admired Ferguson rifle, the gas leakage around the vertical screw breech blows my hat off.... ...no harm no foul.  It sure isn't water tight.
     
Now none of this is to say that a poorly fitted breech plug is a good idea or that one should not try ones best to fit a plug properly, but don't get too carried away with fear and superstition about the effectiveness of the seal between the plug and the bore.  Turtle's Blue Locktite option is an excellent way to enhance the seal between the plug and the female threads, prevent corrosion, and make sure that if you ever need to pull the breech plug, it will come out cleanly.  And for those who think this option is not HC or PC .....or whatever....don't pull the plug on most original rifles.  The course threads and short engagement will scare you to death.

Sorry.....this may be more like my 3 cents on this subject rather than just 2.....

[jerrywh]

Davec2
   I'm glad you enlightened some of the guys. I put plumbers dope on most of mine. I'm sure I will receive lots of criticism for that but it works good enough with a well fit plug.

[alacran]

Davec2
   I'm glad you enlightened some of the guys. I put plumbers dope on most of mine. I'm sure I will receive lots of criticism for that but it works good enough with a well fit plug.

I tried not to weigh in on this topic, but I just can't help making a couple of comments.

1.  First and foremost, Yes, a breech plug should be well fitted
2.  In my business (rocket engines) I routinely seal helium and hydrogen systems (MUCH more difficult to do than powder gasses) up to 10,000 psi and other types of gas systems up to 35,000 psi.  I think I am familiar with sealing high pressure, and often very hot, gasses (in excess of 5500 degrees F).  Anyone who thinks that even a well fitted, straight thread plug with an excellent interference fit on a well machined shoulder can seal hot gas at 10,000 psi is....well... not well informed.  No one worth his salt in my business would design a metallic seal like that with any hope of success. 
3.  The many breech plugs that don't appear to leak hot gas during shooting don't leak for a few very specific reasons.....

       a) The pressure pulse created in the bore during firing is very short...i.e. milliseconds....about 3.6 milliseconds for a 48 inch barrel ...and the pressure is dropping the
           whole time. 
       b) The threads themselves form what is often referred to as a "labyrinth seal"...i.e. every time the gas tries to go around a corner, or through a very restricted space, it
           drops in pressure.  The same as putting a restricting orifice in a gas line to choke down the flow rate.
       c) The first bit of powder fouling that gets driven into any leak path around the breech shoulder and first couple of threads forms a packing that enhances the "labyrinth"
           effectiveness.
       d) NO flintlock breech is water or gas tight....we all purposely drill a hole in the breech area that lets fire in and gas out.  Without a toothpick, they all leak water.
       e) Every time I fire my much admired Ferguson rifle, the gas leakage around the vertical screw breech blows my hat off.... ...no harm no foul.  It sure isn't water tight.
     
Now none of this is to say that a poorly fitted breech plug is a good idea or that one should not try ones best to fit a plug properly, but don't get too carried away with fear and superstition about the effectiveness of the seal between the plug and the bore.  Turtle's Blue Locktite option is an excellent way to enhance the seal between the plug and the female threads, prevent corrosion, and make sure that if you ever need to pull the breech plug, it will come out cleanly.  And for those who think this option is not HC or PC .....or whatever....don't pull the plug on most original rifles.  The course threads and short engagement will scare you to death.

Sorry.....this may be more like my 3 cents on this subject rather than just 2.....

Thank you.

[oldarcher]

I am not sure why this topic has received so many replies that all seem to agree: The plug should be as tight as possible and NOT leak water or gas. If you have any noticeable gas or water leakage, find a competent BP gunsmith and have him carefully check the breech. BP Gunsmithing is not rocket science, it requires a competent machinist to carefully fit a plug or determine if the rifle is safe. Dave2 is absolutely correct concerning the "labyrinth" of threads, however the percentage of contact of the threads is an important factor, most thread applications do not allow for 100% thread contact as the plug (bolt) could not be fitted, most applications are somewhere between 65-80% contact which will allow the fixture to fit the tapped hole. (the npt thread was developed to actually provide more contact and provide a better metal to metal seal, those npt threads still require a sealer of some appropriate kind). This allows a gap to exist and should be filled with some type of sealer. I use blue Loctite, however any suitable high pressure filler (sealer) is better than nothing.     
The breech loading Ferguson rifle is designed to be lowered then returned to battery before firing. The rifle will blow gasses by because metal to metal contact will not seal gasses. NOT AT ALL SIMILAR TO COMMON BP GUNS. The common BP gun is not to leak gasses as that is an indication of a loose  or improper fitted breech.  Just my 2 cents.

[davec2]

John,

Thanks so much for the pictures !

Dave C

[M. E. Pering]

Number 3 in that picture set must be the oldest.  Incredible how they relied on so little to do so much.  Notice also how thin the tang is on that plug.  Also notice the small notch in the upper part of the tang, a possible allowance for a thread plate to be turned just a bit further, since many of the threads were swaged, and not cut.  The deeper threads help with strength, but as far as creating a seal, that would be worthless.  And there are stories of breeches blowing... Probably more from the corrosion that occurred rather than the weakness of the original breech. 

JTR... Thanks for the pics... They really do add to the perspective of how we think today, and how men thought 150-200 years ago.  Do you have any dates for these plugs?

Matt

[alacran]

Helped a friend re breach his great, great grandfathers gun a couple of years back. The plug looked like # 3 in the pictures. The plug was not the issue, the drum had blown out due to all the cap flash corrosion.  The threads on the drum weren't very impressive either.
Cut of three inches of the breech to get past the corrosion.

[Daryl]

To give example to davec2 comment regarding original breech plugs and their fit, here's a picture of a few original plugs.
The first pic shows 5 plugs, the top two plugs with a piece of their original barrel.
The second pic shows the same plugs, except the top two have been screwed into the barrel threads, Only Finger Tight! The top one needs about 1/2 turn to seat it fully, and the 2nd one needs only a bit over 1/4 turn to fully seat it, with a wrench.

These plugs and their fit to the barrel are very consistent with what you will find with most original longrifles.

I'm not saying this is the way you should do it, just showing the way it was done, for those of you that haven't had the chance to see them first hand.
John
 

Today, you can get a fit, just like the 3rd one down, in an Indian Made Brown Bess, having 3 male threads with .003" to .022" engagement in female threads that are .060" to .070" deep.

[JTR]

Your welcome Dave.
Matt, I don't know the actual dates on most of these plugs. I do know the top one is from a 1800-ish Lancaster rifle.
Over the years I bought all sorts of old parts, barrels, locks, etc, to help me with my restoration work. Some were for possible future use, but most bought just so I could learn how the ol boys did it, to help me be more accurate when working on a gun.

Here's a couple pictures of a well worn breech, on an original percussion rifle! If you look close you'll notice that the barrel had at some point already been cut back. Percussion caps were bad news for the iron of the day!