what is the smallest diameter drum i can use?

[MDL]

I am building a kentucky style caplock pistol. I have a precut stock with the barrel channel already cut in it, the barrel is 13/16 40cal. and an L&R Manton caplock. The side panel is a little small to get the lock in along the bottom. I need to move the lock up a little I have a 5/16-24 threaded drum that I turned down to 0.3800. I was wondering if I can turn that down anymore and still be safe to shoot?

[smylee grouch]

A picture of the stock/.lock might help>

[D. Taylor Sapergia]

Something wrong with your math Sir. 
A 5/16" drum is .3125" in diameter.  You cannot turn it down to .380" - that's over 3/8" in diameter.  I submit that your drum was 7/16" or .4375".  Is there a circular cut-out in the percussion plate for the drum?  What size is it?
The devil is in the details, as they say.

[MDL]

The drum was 7/16 in diameter with a 5/16-24 thread that I turned down to 0.380. I was wondering if I can go smaller and still be safe. Can I make a 5/16 drum with 1/4-28 threads and have that still be safe to shoot with 20gr. of powder?

Here are some pictures. Thank you for your help.









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[okieboy]

 You could make a 5/16--5/16-32 thread drum and just bottom it on the thread runout. I personally believe that a problem with 1/4" threads for a drum is how thin the wall of the drum becomes under the threads(minor thread diameter minus internal hole diameter divided by two). Minor thread diameter on an external thread is the distance between the bottoms of threads on the opposite sides. The thin walls leave little material for apsorbing the impact of the hammer and the material stress it causes.

[MDL]

Thanks for that reply I hadn't considered the issue of the hammer strikes over time on the threads, I was more concerned with the pressures the powder would create.

[Ted Kramer]

MDL-
You haven’t started to inlet the  Manton yet, ever consider a different lock that’d fit better on the lock panel?
Ted K

[MDL]

I tried small siler the back end fit better but the front was about the same unless I set it crooked in the panel and i didn't like the look of it.  Being left handed I don't have as many locks to choose from. I tried to find a Becky lock but couldn't find one of those either.

[Clowdis]

Can't you modify the lock plate to fit the 7/16 diameter drum?

[MDL]

The main spring sits right beneath the drum in the lock plate, I filed some of that away but I am afraid to take to much material away because of the spring

[D. Taylor Sapergia]

Why do you want a drum of smaller diameter?