Ferguson rifle question- breeching wall thickness

[ddoyle]

trying to sort out how to attach a ferguson breech to a barrel. I originally thought the magic of a Ferguson was in the multi start thread- turns out that is the easy part, making a rifle out of it seems to be what seperates the hacks (me) from the gunbuilders (someone else),  I spent alot of time over the past couple years building up a machine to cut/index 10, 11 and 12 start threads with 1 and .75 leads- the joy of success was short lived and  used up all my creative energy so lest the project stall and mothball I am hoping for some ideas- guesses or spitballs anything to try and get over the hump.

My quandry is thus: Once we add up the generous tapered chamber diameter- the wall of the chamber- the wall of the barrel and the thread to attach the two it is dang near impossible keep a .62 cal rifle (especially one with deep grooves) from having a breech way in excess of what Durs pulled off.  Does'nt seem to make a difference wether the chamber is in the barrel or in the breech and it does not seem to matter if we thread the barrel male or female. bought every book, old magazine,  journal,  that even mentions Ferguson and the #513 TRS plan but no joy

I can make a .50 work and maybe even a .58 and come in at the breech diameter of an OEM Ferguson but not a proper calibre rifle.

For present math I am using 28 tpi or > for a breech/barrel thread and have drawn things out with a tapered attachement that matches the taper of the chamber to try and preserve wall thickness.

The question that keeps surfacing for me but which I cannot even guess about is  how to determine minimum wall thickness for a "supported" chamber/barrel. i.e the wall of the chamber that is screwed into the barrel or the wall of the barrel that is screwed into the breech? Currently I am using what I consider the minimum wall thickness and applying it to both parts.  

i.e if I think I need .xxx wall thickness at the breech do I need that in both parts or can the thickness be reduced on the parts that are threaded together/overlap offer some support?

By way of exchange I can offer the following (for me) hard won bit of learnin-  An easy way to cut the above mentioned range of threads useful for Ferguson type breeches  is to cut/aqquire a pinion for your lead screw that allows you to in one revolution of it to measure the lead you are trying to cut and then to make a dial that is divided to indicate the  pitches ). i.e a pinion and dial that is custom made for the lead and starts. I went thru about a half dozen other methods and for me and my machine they all had some drawbacks. The custom pinion method allows you to keep the mandrel and lead screw in phase no matter how creative you are in messing up or in loosing focus.  Caveate- my leadscrew is 16tpi and toy like so your milage may vary if you own a real lathe. 
 

[Bill Paton]

I am a bit confused. I am picturing you making your plug and chamber separate from the barrel and screwing them together like a patent breech, or like a Lindsay double musket did. My Ferguson ordnance rifle by Ernie Cowan (patterned meticulously after the Morristown rifle) has a barrel/chamber/female plug thread all as one forged unit with no joint. A short breech plug at the rear of the plug seals off the back of the barrel. Maybe you can clear my head if I am wrong.

Bill Paton

[ddoyle]

Hi Bill,

Ahhhhhh that clears it up. Yes you have interpretted my folly correctly. I am trying to screw a patent like breech into the end of barrel, wow I am kind of floored that I got this far and completely missed it.

 That said if I had been smart enough to call you when you generously offered..... trouble was I was too ignorant at the time to form the right questions and kept putting it off till I could talk more intelligently- mistake cause I still can't talk intelligently .  I really wish I had exploited the aid when it was offered! Your a good man for even humouring this latest request.

  Thinking out loud-  I am guessing Ernie holds the barrel on the saddle orientated perpendicular to the ways and line bores the female thread. (holds a bar with the tool between centers and drives it with a dog) some how counterbalances the overhung wieght or has a machine big enough to ignore it.

 Maybe I can live with a .5o cal ferguson sporting rifle with the lead adjusted to suit  or maybe this is the push for a larger lathe.

------ I am gonna  brew a fresh thermos and head off to my thinking stump.  Huge thanks Bill.

[jerrywh]

 The guy who can answer these questions for you is Davc2.  He is an engineer and a expert on ordinance. He has also built a Ferguson

[ddoyle]

Jerry,

Thanks for the lead,  I am an admirer (obvioulsy) of Dave's work but missed his TRS Ferguson. Those photos he took are simply priceless. Once I fully digest the reality that Bill provided I'll consider consulting a rocket engineer and pre-eminent artist but I am a bit leary of taking more then about 8 seconds from whatever he is working on!

I think at this point, in true UEL fashion,  I am going to adjust my expectations and carry on with a .50 or .54  with a breech screw lead to match. On the plus side a smaller cal with a slower lead gives more sealing pitches for a given breech size  so maybe that is for the best.  It has been  a couple centuries + since anyone in my family fired or saw a Carbine bore Ferguson rifle so we can probabley wait a bit more for my understanding/skill to catch up with the OEM technology.


Thanks again for the help over the hump.