breech plugs

[Col. Batguano]

With so much steel (relative to the barrel wall thickness, and so many threads engaging, are there instances of breech plugs actually failing? That's a lot of bearing surface to provide reinforcement.

That said, I recently needed to weld a tang back on to a plug that snapped off. the other day I noticed that the tang was now so soft that I could bend it with just relatively slight hand pressure. Do I need to heat treat, quench, and then temper the steel in the plug/tang area to make it safe for shooting? Or, sad as it is, do I just need to get a whole new plug for it, re'shape and start over? That will be a bit of a lift, because it's a 38 caliber plug. Not an every day caliber.

 

[Zonie]

Unless you used a carbon steel with at least 45 points of carbon like 1045, don't bother trying to heat treat it. It won't harden enough to be worth the bother.

In fact, a steel with 18 to 20 points of carbon like 1018 or 1020 won't harden at all.
Neither will 12L14.

As for safety, breech threads on modern muzzleloading rifles are very overdesigned.

If the threads are in good condition and there is 5/8" or more of thread engagement all should be well.

 

[Col. Batguano]

That was my thought too. Lots of steel there, plus, it's also held in place by the inlet in the stock, and tang bolt, as is the barrel by the lugs. Neither piece is going to go anywhere in the event of a "fail". I mean, what really CAN fail?

How to keep the tang from being extra flexible and bendy then? I haven't even started profiling it and the breech, so it's still its' full and original .200" (or so) thickness. My only thought there was to harden it and then treat it, just like we do with frizzens. Get it soft to engrave, and then harden and temper to actually use.

 

[Zonie]

A short talk about "bendy or flexibility qualities of materials:

I'll start by saying, if the tang thickness is.200", it is going to take a LOT of force to bend it far enough so that it won't return to its original shape.

That said, the only things that determine the amount a part will bend under a given load on a piece of bar with a cross section of a rectangle is, the width, the thickness, the length from the support to the place where the load is being applied and the "modulus of elasticity" of the material.

This "modulus of elasticity" is basically the ability of a material to resist bending.

The modulus of elasticity for soft steel is roughly 30 million psi.
The modulus of elasticity of hardened steel is roughly 30 million psi.

In other words, the amount a rectangular cross section piece of steel will bend depends on its thickness, its width and its length.
Hardness of the steel has nothing to do with it.

Don't get me wrong. The ability of the steel part to return to its original shape after the load is removed changes a lot with the parts hardness.
That's why a soft untempered piece of steel won't work as a spring but the same piece of steel that is hardened and tempered will make an excellent spring.

Speaking of the tangs width, thickness and length, the width and length do not have the same effect as the thickness does.

Thickness works as a "cube" of the value so making it thinner just a little will let it bend MUCH easier.

If your interested, regular stainless steel (austenitic types) has a modulus of elasticity of 29 million psi so a given size will bend more than the same size piece of carbon steel.
(The smaller the value, the less resistance to bending.)

Nickle alloys MOE = 34 X 10^6
Copper = 18.7 X 10^6
Lead = 2 X 10^6

 

[eggwelder]

tap for the barrel- what type do you use?

 

[Elnathan]

Eggwelder,

Do you by any chance have a copy of this book? https://www.amazon.com/Gunsmiths-M...=1486594280&sr=8-1&keywords=gunsmith's+manual

 

[Elnathan]

If the threads are in good condition and there is 5/8" or more of thread engagement all should be well.

Rice Barrels is now using 1/2"

 

[eggwelder]

i do not but will in about 2 weeks. there is no rush for this project so i am researching it as much as i can. it is intended to be a learning project that pokes holes in stuff....

 

[Walks with fire]

On a 15/16" .54 barrel that uses a 5/8 x 18 breech plug there is not much of a shoulder to butt the plug face into. Going to the 3/4 may be a better way to go. I don't know what steel is used to make allen wrenches but it would simplify things I would think. One could be made on a vertical mill pretty easy.

 

[eggwelder]

Eggwelder,

Do you by any chance have a copy of this book? https://www.amazon.com/Gunsmiths-M...280&sr=8-1&keywords=gunsmith's+manual[/quote]

The book arrived today, and i am very glad you recommended it. looks like i may be modifying some taps.
lots of valuable info that relates to this hobby for those interested in that aspect.