5/16 NF drum threads

[Scota4570]

I look at the drum and the flame channel as get the impression it could be stronger and better. 

The flame channel is narrow which will cause misfires.  The threads are small which may cause the drum to eventually depart the barrel? 

This barrel could accommodate 3/8 NF threads.  A 3/8" drum can safely have a larger flame channel.  I like the powder under the nipple.  Reliability is super important to me, especially on a rifle I may hunt with. 

Am I over-analyzing again?

[D. Taylor Sapergia]

I don't think you're over-obsessing.  If I were making a drum for a percussion rifle, I'd make the thread journal 3/8" x 24, but the drum itself I'd turn to 1/2".  That way, the drum bottoms against the side of the barrel flat TIGHTLY!  This is important, as you don't want the drum to loosen and start to rotate.  The obvious problem is safety, and the less obvious is the alignment of the hammer and the nipple.  The 1/2" drum offers lots of material into which to drill and tap for the nipple seat too.  The flash channel can easily be #10 drill.  There are a few percussion locks that are cut for a drum, and I believe they are around 1/2" radius, but could be 7/16".  It has been about 40 years since I last built a rifle with a percussion lock and drum and nipple, so my "memory is like a bunny's tail...short and fuzzy".  Quote from my buddy Neil Hunter.
I'm in the process of acquiring a Bill Large barrel that I intend to build into a percussion Bedford Co. rifle, so these thoughts are also going through my melon too.

[Scota4570]

This build requires a 9/16" drum.  It is my Leman project. 

[okieboy]

 The flash channel on a commercial 3/8-24 drum is about .150". The minor diameter of a 3/8-24 is .323". .323-.150=.173". .173/2 = .086" wall thickness. Point being, you probably do not want to increase the diameter of the flash channel. You could bring the inside face of the drum flush with the inside diameter of the bore it is being screwed into and then do some judicious and thought out cone-ing to the flash channel similar to a touch hole liner.
 A real question about making the best drum is what material to start with. I have been comparing S7 tool steel and 1144 stressproof. My personal conclusion was that for me, the stressproof was my choice as I could get good physical properties without heat treating. I would not trust my blacksmith heat treating techniques for S7 tool steel. I just purchased some stressproof, but other projects are ahead of cutting into it.
 These are strictly my own thoughts and I am sure others may disagree. 

[Dale Halterman]

Taylor, if you are using an L&R Bedford lock they are cut for a 7/16" drum.

Dale H

[hudson]

I normally use grade 8 bolts already heat treated and machining has not been a problem. Remember a nipple has a shank ¼ “long and protrudes into the flash channel on those small drums.

[Scota4570]

The drum I got with the parts set is 5/16 NF with a 9/16 Drum OD.  The hole in the middle is 5/32" leaving 0.57" wall thickness.  To me that seems sketchy.

I will be installing it in a solid chambered breech plug with full sealing just like a properly done breech thread with an internal shoulder.  Sort of like CVA but not so deep. 

IF I make a drum with 3/8 NF threads the wall thickness is the following, 5/32 hole 0.088", 3/16 hole .071", and 7/32 hole 0.055".

It appears to me I can make the hole a bit larger, 3/16,  and still gain strength with a 3/8" NF threaded drum.

As an aside I wish I had made the chambered breech plug differently.  I made it like a flint plug, following the barrel contour.  I used square stock to machine it from.  If had left the chambered breech plug square on the drum side it could have more fully fully supported the drum against the hammer blows.  I could have machined the plug so it looked like the drum and plug were one piece.  Maybe next time?

[Elnathan]

 A real question about making the best drum is what material to start with. I have been comparing S7 tool steel and 1144 stressproof. My personal conclusion was that for me, the stressproof was my choice as I could get good physical properties without heat treating. I would not trust my blacksmith heat treating techniques for S7 tool steel. I just purchased some stressproof, but other projects are ahead of cutting into it.
 These are strictly my own thoughts and I am sure others may disagree.

Stressproof has poor ductility and accordingly poor strength under shock impact, I believe. Since a drum takes part of the force of the powder detonation, ability to take shock impact is an important consideration, I'd think.

[okieboy]

 Elnathan, since stressproof is specifically recommended for repetitive stress applications, could you offer some documentation to support your statement. Where are you seeing that stressproof has poor ductility?
 I am asking respectfully, I have been a metalworker most of my life, but for all I know you may be a metallurgist. I will be happy to improve my knowledge, but would appreciate some data sources. 

[Elnathan]

Okieboy,

PM sent.

[Bob Roller]

Another thing to look at is to be sure the drum is snug against the lock plate.
I have seen more than one botched job of fitting in this area and no apparent concern
about it.
Bob Roller