Breech plugs - why do they have to be screwed in so tight?

[bones92]

It seems that many breech plugs are screwed in really tight, if my reading of posts in this and other forums is any indication.

Why is this the case?  Isn't the most important thing to have a sufficient number of properly-fitted threads on the plug and breech?   Or is it a matter of who does the threading/machining... meaning, some may tap the breech in a manner that makes it inherently difficult to screw the plug all the way in, with a bit of a taper to thread walls?

Please forgive me for such a basic question.  I truly want to understand this.  It would seem to me that a breech plug screwed all the way in and tightened with a wrench in one hand while holding the barrel in the other should suffice, as long as the plug is indexed accurately.

Okay, fire away at the greenhorn... I can take it. 

[rich pierce]

I bet the barrel makers who supply barrels breeched want zero chance that a customer will tighten the breechplug past index. Plus lawsuits plus reputation. Nothing would ruin a barrel maker like "Hey I got one with a loose breech plug!"  They are probably following normal machining standards developed for center fire barrels and actions.

[D. Taylor Sapergia]

It would seem to me that a breech plug screwed all the way in and tightened with a wrench in one hand while holding the barrel in the other should suffice, as long as the plug is indexed accurately.

That in my mind, is a little on the light side.  But having secured the barrel solidly in a bench vise, a 12" wrench bumping the plug into place, is reasonable.  One should be able to remove the plug at any time without marking either the barrel or the plug.

[D. Taylor Sapergia]

Valid point Rich.

[kutter]

The plug needs to do a few things when it's installed.
It's face needs to form a gas tight seal against the opposing machined surface in the bbl threaded seat. Probably the most important point.
That's the primary point of contact betw the plug and the bbl.
Tight is tight, but strong arm tightening to make up for a poor fit here doesn't usually work.

The plug tang must index with the top of the bbl, but the bolster itself need not actually fit the back of the bbl flat as tightly as the above. In fact if it didn't touch at all and the above fit was perfect, it would do it's job nicely. It just wouldn't pass most gunmakers visual test.
I like them to seat inside perfectly as I can get them for the gas tight seal. Then tighten down with the bbl in a vise and a 10 or 12" plug wrench to pull it into place is fine IMO.
The back of the bbl and the tang bolsters should make contact but just barely. Again JMO.

I ask people who insist on extra gorilla power to tighten up the breech plug,,how much of that do you put into the installation of a vent insert? Usually done w/a screwdriver and it feels the same breech psi as the plug.

Standing on extra long cheater bar extensions slid over plug wrench handles to install or remove plugs is as foolish as it is in barreling or rebarreling a cartridge firearm. It usually shows that something was done wrong in the fit-up to begin with and the difference is being made up with brute strength.

[rfd]

who's breech plug and what type?

the commercial production guns that employ patent breech plugs that are practically welded on so they can't be removed.  this includes traditions, cva, pedersoli and others.  investarms plugs can usually be removed with the right tools but they're on *tight* and never lubed.  worse yet, for the near dozen i've seen and worked on, they're never cleaned after proofing.

as long as an anti-seize lube is used, custom barrels with flat faced breech plugs are spun on tight enuf to be removed with a rice barrel wrench and hit the witness mark every time.  i think the thread tpi and pitch that allows the right amount of tight thread fit is a good thing, to mitigate gas blow back, along with the use of a good thread lube.

a brand new investarms patent breech, only proofed.  look at that crud ...





since it's a patent breech, can't use a rice wrench, i use an 18" reed corp ...

[Bob Roller]

who's breech plug and what type?

the commercial production guns that employ patent breech plugs that are practically welded on so they can't be removed.  this includes traditions, cva, pedersoli and others.  investarms plugs can usually be removed with the right tools but they're on *tight* and never lubed.  worse yet, for the near dozen i've seen and worked on, they're never cleaned after proofing.

as long as an anti-seize lube is used, custom barrels with flat faced breech plugs are spun on tight enuf to be removed with a rice barrel wrench and hit the witness mark every time.  i think the thread tpi and pitch that allows the right amount of tight thread fit is a good thing, and ditto's for the use of the thread lube.

a brand new investarms patent breech, only proofed.  look at that crud ...





since it's a patent breech, can't use a rice wrench, i use an 18" reed corp ...

I'd be skeptical of that Adjustable wrench.A 6 point socket either decimal or metric and
along handle would be a better choice IMHO.
WHAT did they proof that gun with? Looks like bad news whatever it was.

Bob Roller

[flehto]

Nothing is perfect.....so bbl makers err on the tight side.....Fred

[bob in the woods]

Long Hammock, Rice, Rayl , Getz, Burton, Colerain, etc ..never had a problem with breech plugs. 

[rfd]

.....

I'd be skeptical of that Adjustable wrench.A 6 point socket either decimal or metric and
along handle would be a better choice IMHO.
WHAT did they proof that gun with? Looks like bad news whatever it was.

Bob Roller

the rcorp massive and flat jawed and locks in tight.  it's nice that one wrench fits many barrels.

i will add - the rcorp is only used for those offshore patent breech plugs.  for classic flat faced plugs i use a rice wrench.

who knows what it was proofed with, but this is typical of those offshore barrels/chambers/breeches.

[Cory Joe Stewart]

The tightness does seem to be different with the manufacturer.  I did have an issue recently with a well known barrel company, where the breech was not touching the face, there was nearly a 1/16 gap.  I will not name names because it was my fault for not double checking before inletting the barrel. 

Coryjoe

[bones92]

Are we talking about the breech plug shoulder touching the face of the barrel (visible externally), or the front surface of the plug resting up against a back-facing shoulder inside the barrel?   My apologies, I'm not familiar with the various breech designs.

[Bob Roller]

Are we talking about the breech plug shoulder touching the face of the barrel (visible externally), or the front surface of the plug resting up against a back-facing shoulder inside the barrel?   My apologies, I'm not familiar with the various breech designs.

BOTH if possible.If not then the plug snugged against the inner surface in the barrel.

Bob Roller

[frogwalking]

I think the proper installation of the plug face fitting tight against the shoulder in the bore and simultaneously having the front of the tang fit tight against the top barrel flat can only be done, one at a time by a skilled and patient workman.  This is expensive.  It is cheaper to get the thing close and put the gorilla on the wrench to accomplish the same type of thing, only with less finesse.
(Someone like me, with less skill and more patience can also get a correct installation, only it will take even longer.)

I suspect the manufacturer also does not want someone knowing little about these rifles removing the plug.  Who knows, he might try to leave the plug a full turn loose rather than making it fit correctly.  Then he will be mad because inexplicably, now nothing fits right.

[Bob Roller]

I think the proper installation of the plug face fitting tight against the shoulder in the bore and simultaneously having the front of the tang fit tight against the top barrel flat can only be done, one at a time by a skilled and patient workman.  This is expensive.  It is cheaper to get the thing close and put the gorilla on the wrench to accomplish the same type of thing, only with less finesse.
(Someone like me, with less skill and more patience can also get a correct installation, only it will take even longer.)

I suspect the manufacturer also does not want someone knowing little about these rifles removing the plug.  Who knows, he might try to leave the plug a full turn loose rather than making it fit correctly.  Then he will be mad because inexplicably, now nothing fits right.

Simultaneous contact IS the BEST and I can do it like I did when helping Bill Large years ago.I turned a blank slightly larger than the OD of the barrel and then turn the shank to threaded to within .002 or closer to the depth of the threaded barrel.Tighten with a pipe wrench then mill it to shape in the Bridgeport milling machine. I have never tried to fit a commercial plug as is common to flint lock guns and cap locks with a drum and nipple and wouldn't want the job.

Bob Roller

[Mike Brooks]

I remember hearing stories about Kit Ravenshere fitting his brown bess breech plugs so you could take them in and out by hand, no vise or tools needed. 

[Ky-Flinter]

I did have an issue recently with a well known barrel company, where the breech was not touching the face, there was nearly a 1/16 gap.  I will not name names because it was my fault for not double checking before inletting the barrel.  

Coryjoe

Breech plugs not properly fitted happens more that one would think, even from the well known suppliers.  I too have seen plugs that were extremely tight, but the plug face wasn't even touching the inner shoulder in the barrel, as CoryJoe described.  I usually end up refitting all my breech plugs because I want to remove the rough machining marks left on the breech plug face, then polish it.  When I'm finished the plug snugs up with a standard wrench, barrel in vise as Taylor described.

-Ron

[bob in the woods]

An older barrel from "Paris" barrels was machined with course threads, not the fine threads we see today. After breaking the plug loose, [ not difficult ], it was a snap to unscrew with your fingers.

[Bob Roller]

I remember hearing stories about Kit Ravenshere fitting his brown bess breech plugs so you could take them in and out by hand, no vise or tools needed. 

I think this comes from the idea that the ball will hopefully MOVE before the plug backs out.
A CW Springfield I had years ago was like that Brown Bess and it never leaked a bit of gas.

Bob Roller

[jerrywh]

Builders often worry too much about breech plugs. On a 50 cal, barrel the pressure is 8 times as much on the barrel as it is on the face of the plug.  So worry about the barrel and keep em clean. I have taken plugs out of 200 year old guns that never even had a face fit or a shoulder fit and the threads were in very good condition. Those plugs often have a tapered type plug and are a force fit almost like a pipe thread but the thread is rounded. Not a V type thread.