So my son is working as a muzzle loader instructor at a scout camp this summer.

They have a bunch of old muzzle loaders, some .50 cal Hawkens' style that he is using in his mountain man program and a bunch of .58 cal rifles they use in their civil war program.

The rifles have been used for quit a few years and many of them are in sad shape.  The biggest problem seems to be knot heads cross threading the nipples after cleaning or using the wrong nipples and stripping out the threads.  Now on most of the .58's if you get get a nipple to fit in the hole it gets blow away when you try to fire a shot.

I was looking around at Track of the Wolf and they have some over size nipples that I think will work for the Hawken's rifles.  But no such thing for the .58 musket cap rifles.

Has anyone ever tried putting a helicoil in a muzzle loader to hold the nipple in place?

Any idea if it would hold up to the pressures?

I tried to tell the camp director he needs to buy new rifles, but they don't really have $5,000-$6,000 to spend on half a dozen rifles.

I dunno if HeliCoil will take the pressure.  These weapons operate on WAY more pressure, than sparkplugs in an aluminum engine block.

Why don't you email them?  The mfg will be more than happy to entertain this oddball question!

You may be in the market for having the nipple holes:

1.  Refreshed with the correct size tap and try to re-insert the old nipples and hope they stay ( maybe OK for simply cross threaded situations)

OR

2. drilled and tapped  to a larger size, and either finding new nipples to fit the weird new threaded hole (sounds unlikely)

OR

3. silver soldering (brazing?) a plug into the hole, and re-drilling and threading it to take the old, traditional sized nipples.

EDIT:  The pressure ceiling you are probably dealing with is on the order of 20ksi, roundly speaking.

http://s.hswstatic.com/gif/flintlock13.jpg

You know, that drum shaped thing the nipple screws into is just probably a threaded cylinder screwed into the barrel wall.

A machine shop w/ a lathe could crank out replacement, uh, "drums" for your rifles, if they don't sell this part online.

#1 on replacing the drums.
It's like refurbishing the riles!

I'm not sure how hard it is to remove a drum, never done it.
I am sure a competent gunsmith could replace them.
Hawkens are common guns so they likely use a common drum.

It's not a drum that the nipple screws into on the civil war rifles.  Looks like it is integral to the barrel.

I don't think a helicoil will stand up to the pressure. A few years ago I was searching for an 1816 conversion musket and during my search, and research, I found where people had in the past repaired damaged muskets with helicoils, and they don't hold. I would check with someone who repairs or manufactures BP barrels.

A helicoil will hold up perfectly fine and are a pretty common method for repairing them (I've fixed dozens of BP rifles damaged the same way).
Helicoils are also made of hardened stainless steel, which is much more
durable than the metal used to make your BP gun. So once you replace the
damaged threads with a helicoil, the coil will usually last longer than
the normal threads would have (and resist cross threading better).
Black
powder and it's substitutes also generate significantly less pressure than smokeless powders (as
it is an explosive, not a propellant), this is why using smokeless in
BP firearms end up blowing them apart with ease. In addition to this,
the available volume for the gasses inside the drum or pathway to the nipple are much smaller than the bore, as well as being vented (the nipple does not seal completely, otherwise there wouldn't be a puff of smoke at the lock), which further reduces pressures experienced by the threads.



Also once you have the helicoil in place, make it a practice to put anti-seize compound (one with graphite and molybdenum, avoid using ones containing lithium as the lithium will burn off and is toxic) on the nipple threads when replacing them after cleaning/repairs.





 

Pressure is probably nearly the same everywhere in the combustion chamber, shortly after ignition.  But the forces involved which the nipple/helicoil system must withstand can be kept small, I suppose, since you are doing it.    I would be surprised if a helicoiled breechplug could survive the pressure cycling long term.  Small fittings seem to stand elevated pressure more easily than large fittings, due to the way pressure acts over larger surface areas to increase the forces involved .

It would be extremely nice if this easy trick can be made to work.   I take you at your word that it does.