Questions / thoughts on original breech plugs versus current day breech plugs

[bedbugbilly]

Mostly curiousity on my part as I sometimes "ponder" on little details . . . 

I read in one of the threads here a comment by a poster that he would prefer a shorter breech plug of 1/2" over the usual 5/8" (length of threaded portion of plug.  When I read it, my thoughts were that if a person had a mill, this would be a simple operation to perform - mill an 1/8" off the breech portion of the barrel and the same off the plug until it fits.  Anyways, it got me to thinking . . .

Over the years, I've worked on a lot of antique front loaders.  It's obvious  that most of the military muskets - .54, .58, .69, etc. had breech plugs that were substantial and utilized fine threads which provided for, what I'll call, "substantial thread catch" (as opposed to coarse threads . . .

I've worked on percussion era long rifles and a number of what I'll call "Ohio" style half stocks and half stocks of the 1850 to 1870 or 1880 era .  . .

Some had patent breeches which had fine threads . . . but many, which utilized drums and nipples, had breech plugs that had extremely course threads and a number of them, the threaded portion were possibly only 1/2" with only 5 or 6 coarse threads to screw in - possibly hand cut threads?

So . . . my question is this.  How common were coarsly threaded breech plugs in the old long rifles?  I'm sure it varied from maker to maker  . . . but were they "common" or when did the practice of utilizing fine threads (more TPI) come in to common use?

I'm not advocating coarse threads . . . obviously more TPI provide for a better mate of the breech plug and barrel . . . . but from my experience in examining some of the rifles with very coarse threaded breech plugs they must have worked O.K. as there were no indications of problems or weakness.  Personally, I feel much safer with the type we use today but am wondering if anyone has ever taken much of a look at the threads used and your thoughts on why some makers used such coarse threads?

Thanks!

[Don Getz]

I have looked at a lot of old barrels and it is rare to see one with fine threads.  The early barrels had very coarse threads and
many times do not match up with the coarse threads that we can now make on a lathe.   When we purchased the Paris barrel
making equipment, we found that they used coarse threads....5/8x11, 3/4x10, and we had to chase plugs on a  lathe.  They
used those early coarse threads since they closely matchd what was found on most old barrels.  We succombed to pressure
from the public who liked the fine threads better, and, to be very honest, were easier to fit to a barrel........Don

[James Wilson Everett]

Guys,

Here is a photo of an original set of breech plug taps with the starting, plug and bottom taps.  They are not standard size as we use today and are closer to the UNF fine threads than the UNC coarse threads.  I actually use similar 18th century type tools to breech my barrels and can say from experience that the fine threads have the great advantage of being easier to form in the breech end of a barrel.  We need to know that in the 18th century, threads were swaged or formed, not cut.  The threading, both male & female does not produce the large cutting chips that we see today.  The process results in a little very fine metal "dust" as the threads are swaged into the soft wrought iron.  Needless to say, this older process would be ever more difficult if coarse threads were to be used.  Even today, it sure is a lot easier to turn a 3/4 inch fine thread tap than a coarse thread tap.

Another note to the strength of threads - a standard nut can be tightened until the bolt shank breaks in tension, assuming both the bolt and nut are of the same tensile strength.  And yet a standard coarse thread nut has only about 2.8 threads!

Jim

[Dphariss]

This is an original breech plug. From a derelict barrel of about 44 cal, best guess with the rust etc.


Drum from the same.


Dan

[Birdhunter]

I don't think that a random equal amount can be removed from the barrel & plug & have it come out on the witness marks on the same flat. It must be in multiples of what distance is taken up by 1 turn according to thread pitch. I think that distance is for example .060" for 18 tpi. per 1 turn. I am not a machinist but there are people on this forum that are so they would be the ones to verify if what I think is correct or not.
Curt

[James Wilson Everett]

Guys,

To really understand the answer to the breech plug thread question, we must also understand how very different the tooling of the period was in comparison with the tooling of today.  Before the advent of what we know as standard UNC/UNF/Metric taps & dies - the gunsmiths used adjustable size thread swage tools to make larger threads.  Threads generally smaller than 1/4" diameter used screw plates with fixed, but non-standard thread forms.  Threads generally larger than 1/4" used thread swage tools with adjustable jaws.  Check this out.  Here is a picture from the set of 18th c gunsmith tools for making the breech plug female threads that has the identical thread pitch as the larger set above.



Both sets were made using the same adjustable thread swage tool which yielded not only the tapered thread forms, but also the two different size tap sets with the identical thread pitch.  Here is a picture of a 19th c adjustable thread swage tool.  I am sure that you can imagine how this tool could give both tapered threads and different size threads with the same pitch.  Functionally, this tool is no different than an earlier, 18th c, thread swage tool.



When making the breech plug male threads, the gunsmith would use the adjustable thread swage on the breech plug pin to gradually decrease the size of the thread outside diameter until it fit into the finished breech plug threads in the barrel.  Often this process resulted in a thread fit in the breech plug that is a good bit tighter than the standard threads we use today.

Jim

[bedbugbilly]

Birdhunter - I think what yo are saying is in response to my remark about shortening the threaded portion of the breech plug and removing some material from the threaded breech of a barrel? 

I should have been a little more clear in what I was talking about.  I was referring to a thread I had read where a gentleman stated he would rather have a thread length of 1/2" instead of 5/8" . . . . and I am talking about breeching a new barrel  All things taken in to consideration - if a person desires only 1/2" in length of breech plug threads on the breech plug - you should be able to remove material from the breech end of the barrel to correspond.  It would of course have to be "fitted" as any breech plug would normally be fitted.  I was referring to a barrel blank.  I was speaking in "general terms" . . . if you shorten the breech plug by a 1/8" then you should be able to shorten the breech of the barrel by a "similar" dimension . . . then fit it as you normally would.  I apoligize for not being real clear on that.

When I have fitted breech plugs to barrels in the past - I don't put a witness mark on the plug and barrel until after the plug is fitted. . .  the the bottom flat of the barrel and bottom of tang for "line up" purposes if the breech plug is removed after build.

Thanks to all for your comments and information - great explanations as to why the threads on originals "were as they were".  The pictures of the original breech plug and drum are very typical of what I hae run across over the years.