Breech plug questions

[ihunts2much]

I bought a H&A action and am starting to build my underhammer. I have a Green mountain .50 cal barrel and started working on installing the breechplug. My first question is the plug that came with the action screws right into the breech with only finger pressure and no resistance, just like a nut and bolt. Is this normal or should I be concerned about loose fit? My next question is about fitting the plug. I filed off the first couple threads to get past the part of the breech that is not bottom tapped. I worked the plug face flat with a file and checked frequently by marking with a sharpie and bottoming it. Once I had a pretty complete circle I honed the face with a fine stone. Now on last check I have a circle with a couple small, less than 1/16" breaks. The face is very flat and I have been tightening with an offset 4" screwdriver. Should I crush fit with more pressure now? which brings up the next question... How tight is tight? any fraction of a turn past making contact? or amount of force on a certain size wrench. This is my first time installing a breech plug, so I just want to make sure I get it right. :idunno:

 

[ihunts2much]

to the top please

 

[David W.]

I bought a H&A action and am starting to build my underhammer. I have a Green mountain .50 cal barrel and started working on installing the breechplug. My first question is the plug that came with the action screws right into the breech with only finger pressure and no resistance, just like a nut and bolt. Is this normal or should I be concerned about loose fit? My next question is about fitting the plug. I filed off the first couple threads to get past the part of the breech that is not bottom tapped. I worked the plug face flat with a file and checked frequently by marking with a sharpie and bottoming it. Once I had a pretty complete circle I honed the face with a fine stone. Now on last check I have a circle with a couple small, less than 1/16" breaks. The face is very flat and I have been tightening with an offset 4" screwdriver. Should I crush fit with more pressure now? which brings up the next question... How tight is tight? any fraction of a turn past making contact? or amount of force on a certain size wrench. This is my first time installing a breech plug, so I just want to make sure I get it right. :idunno:

The only answer I can give, you probably do not have the right tools. Not many people have a breech plug wrench on hand. You need somehwere around 80 ft. lb torque, I think. It is kind of like setting lug nuts on a car tire.

 

[Capt. Fred]

There are guys here with way more experience than myself but I'll chime in with how I do it. The GM breech plugs I've done do screw in pretty easily so that is the way the threads fit.

Regarding how tight? I use a 12 inch adjustable wrench and I torque them in as tight as I can with that tool and my 225 lbs of pure fire breathing muscle (LOL). In other words I torque it pretty dang tight.

Are you bottomed out evenly on the back end of the barrel too?

 

[necchi]

That's a good way too explain it to a feller without tools. And I'd say about right,
A 10-12" cresent would allow enough leverage, then using that tool get it as tight as you can without spinning the barrel out of the vise or lifting the table.
In other words, pretty darn tight.

 

[fitter]

I don't have a breech plug wrench either. Like cap. fred end necci have said i've been using either a 12" adjustable wrench or a stilson wrench fo 40 years

 

[fitter]

Sounds like you are doing fine. Put the GM logo on the bottom and you should be ok.

 

[John Taylor]

I install more than a few breach plugs. The 80 pound torque will work but you can get by with less. The main thing is to have a good seal of the breach and it sounds like you have that. A crush fit only makes the seal better. Some lube on the threads will help and make it easier to remove if you need to. Most of the time on under hammers I use a pipe wrench and tighten and loosen a few times to make sure there is a good seat for the seal. Then the rear portion of the plug is turned to fit the frame, which removes the pipe wrench marks. Any where from 40 to 80 pounds of torque is fine, Don't need the 200 +.

 

[David W.]

I install more than a few breach plugs. The 80 pound torque will work but you can get by with less. The main thing is to have a good seal of the breach and it sounds like you have that. A crush fit only makes the seal better. Some lube on the threads will help and make it easier to remove if you need to. Most of the time on under hammers I use a pipe wrench and tighten and loosen a few times to make sure there is a good seat for the seal. Then the rear portion of the plug is turned to fit the frame, which removes the pipe wrench marks. Any where from 40 to 80 pounds of torque is fine, Don't need the 200 +.

The 80 ft. lb was more of a guess. 40 maybe, I would think it should be at least 60, but I have only installed one in my life. I forgot to mention anti-seize for the threads.

 

[ihunts2much]

Thanks for the replies. Here is what i did, I put the barrel in good stout vise, marked the breech plug with a sharpie and tightened lightly with a 12" pipe wrench, which took it a good bit tighter than the offset scredriver I was using before. I backed the plug out and was happy to see a good complete circle of contact. I lubed the threads with graphited ant-seize, threaded in the plug and drove it home with the 12" pipe wrench. As a 6'4" 260lb oaf I have stripped, broke and over-tightened enough in my day to gain a bit of finesse and "know when to stop". I would guess I put around 60 ft lbs on it, it went about 1/16 of a turn past where it previously made contact. I ran a test shot this morning with 60gr and a PRB. It held up with no evidence of leakage. Success!

 

[Capt. Fred]

That sounds good.

By the way, when I stated I used my 225 lbs to tighten it, I didn't mean 225 lbs of torque!! :shocked2: I figured the LOL would make that clear to everybody. Apparently not. :thumbsup:

 

[ohio ramrod]

Long before starting working on guns I worked as an auto mechanic's helper. He impressed on me the importance of the use of a torque wrench. I torgue all of my breech plugs to between 75 and 80 lbs. Lubed with either antisieze or permatex gasget coumpound. :hmm:

 

[Zonie]

The following values are based on a SAE J429 Grade 2 bolt which is made from the mild steel that is very similar to the steels used in muzzleloading guns barrels and breech plugs.

Before I get to the torque values I need to point out that the values given are for a bolt who's only job is to hold things together.

This is not the case with a breech plug.

A breech plug needs to save much its strength for the pressures from firing the gun. It cannot use up all of its strength just holding the plug in the barrel due to torque because it won't have any reserve strength left to withstand the blast pressures.

9/16-18: Fastener torque=53 ft/lb. Breech plug torque = 28 ft/lb (based on 21 KPSI breech pressure)

5/8-18: Fastener torque = 82 ft/lb. Breech plug torque = 56 ft/lb (Based on 15 KPSI breech pressure)

3/4-16: Fastener torque = 144 ft/lb. Breech plug torque = 98 ft/lb (based on 15 KPSI breech pressure)

I must stress that the Breech Plug torques should be considered as Maximum values. If the breech plug is torqued to a lower value so much the better as long as the flat lines up with the barrel flat.

 

Since you are doing an underhammer, I presume with no tang, just a post or stub, it's much easier to get a good seal of the breach to the barrel, providing it's square. Since you have almost nothing to grab unto if you wish to remove it other than the stub, you may not want to torque it much beyond 30 pounds. For the others out there, how does 80 pounds ensure proper fit between breach face and barrel shoulder, while getting the tang to properly align with a barrel flat. I have a number of originals that are just hand tight, maybe 5 to 10 pounds, and they have withstood around two hundred years of shooting. What they have in common is proper fit. Using marker dye I get the plug face to just fit flush at between 1/2 and one full flat short of the flat I want, then use a wrench to tighten from there. Hasn't failed me in 40 years so far. Remember you have a tang bolt, and channel to hold the tang, and a barrel channel, and tenons to hold the barrel. Some of my original plugs were as short as 3/8" with very course threads, but have held for almost 200 years or more, because of proper fit. With an underhammer you have a stub on the breach that has a tapered pin that locks it to the frame adding more load to the plug as it pulls the barrel tight to the frame. Good luck with your project.

Bill

PS, Like sex, and good Bourbon, there's no such thing as too much