Powder drum shim

[RSVP2RIP]

Can someone please tell me why it is not advised to shim a powder drum to get the nipple to line up. If there is enough extra thread to get full engagement into the barrel, is this a saftey issue? I have to go about 5 degrees back or 355 degrees foward.

 

[Preposterous!]

I'm guessing it's simply to ensure that the thread is fully engaged and the nipple is fully seated. Having said that, I use plumber's PTFE tape on mine to guard against erosion/seizure and have no issues.

Maybe worth trying?

 

[RSVP2RIP]

I use nickel or copper grade anti sieze compound for that. Being a pipefitter makes me cringe when people use teflon tape for anything other than a tapered pipe thread (NPT in the USA) lubricant, but if it works for you then thats OK. If the drum makes full contact against the barrel flat with the washer I don't think it will break off under the blow of the hammer, but I'm just guessing as to why not.

 

[mykeal]

The issue is bending moment load on the drum. The further the drum is away from the barrel the larger the bending moment that's exerted at the junction, and the smaller cross section that's available to take that moment. Adding the shim doesn't change any of that, including dissipating the stress resulting from the hammer blow. It will relieve some strain by not allowing bending motion, but it won't relieve any of the load the joint has to withstand.

The most likely failure will be low cycle fatigue at the bottom of the first thread groove in the drum's male threads. Catastrophic failure from one hammer blow is highly unlikely, but premature failure of the drum stem is virtually guaranteed due to repeated blows.

 

[whosyrdaddy]

Just to give this some perspective, I threw some figures together. I don't know the thread pitch of your particular drum but I see that 24 and 28 seem common enough. So lets say it's 24. That means every 360 degree turn moves the drum .04166 inches farther/closer to the breech.

To stop the nipple 5 degrees back, you would need a shim with a thickness of .000578 inches, or about one thicknesses of standard Reynolds Wrap foil.

Whatever material you choose would need to be able to resist the compression forces exerted on the bottom side of the joint ( directly opposite of the nipple ).


The math:
1" divided by 24 threads per inch = .04166" lateral travel per revolution.
one revolution is 360 degrees or 72 5 degree increments.
one revolution lateral travel .04166" divided by 72 = .000578"

 

[rivraton]

Have you considered reworking the hammer instead?

 

[mykeal]

Reworking the hammer by heating and bending is one good solution; it's not difficult and will not materially damage the hammer. Another solution is to rework the lock inletting with wood filler to tilt the top of the lock outward. Very little filler is needed to obtain a significant relocation of the end of the hammer.

 

[sundance44s]

Nipple drums can be bought as blanks ( not pre threaded for the nipple )just threaded for screwing into the barrel , you have to locate the right place to drill and tap the nipple threads , this way the drum will be tight flush with the barrel and the nipple in the right place .
This is how gun builders always get it right .

 

[rusty from italy]

I have put a shim in a drum that goes too forward, i made it from a thin brass foil, it's work good enogh for me
ciao
Rusty

 

[Chawbaccer]

Is it that hard to fit the drum? File evenly around the base and take of a little bit, whosyrdaddy said the shim would just be the thickness of foil. That would be the amoung to take off too. I fit a Colt arbor pin like that so the wedge slot lines up

 

[arcticap]

Doing it that way, I believe that the drum would need to be rotated 355 degrees forward, which would require taking considerably more metal off of the drum base as opposed to doing it the other way with an ultra thin shim.
And the amount that the drum stem imposes into the breech could also be affected which would beg for further study to evaluate any side effects resulting from employing that method.
The precision required to file away the "exact" proper amount off of the drum base and around the stem could also be problematic and risky.
Maybe a shim isn't even needed if the drum only needs to be backed out by 5 degrees? If the friction of the threads will hold it in place and keep it from turning, then why loosen up the threads by taking it all of the way out and then turning it back it in just to install a possibly "unnecessary" shim?
As long the cap goes off, I personally would not turn the drum. I would either leave it alone or possibly try to level off either: 1) the nipple to better engage the face of the hammer or 2) or dremel the flat face of the hammer to match the angle of the nipple.
Since a nipple is very inexpensive, I would try altering the nipple first.
And it's possible that doing anything is taking an unnecessary risk because it works as it is and sometimes tinkering can lead to damaging parts.

 

[Chawbaccer]

Gotcha Arcticap, I wasn't thinking.
Just pull the drum off and use a center punch to make a few dimples around the base. Go easy and you should be able to tighten it right up to where you want.

 

[RSVP2RIP]

Well the reason behind all this is the fact that the nipples get really beat up after a few firings. The leading edge of the cone gets flattened and it becomes hard to seat a cap on it. The hammer spring is real strong and all the caps go off. Bending moment load? Who's a civil engineer here? I don't think the forces involved are that great that a fairly mild steel 5/16x24 thread is going to suffer that much. I should notice plastic deformation before I reach any kind of fatuige failure on the powder drum, ie. there will be a little angle-in-the-dangle before it breaks off.

 

[mykeal]

You're welcome.

 

[arcticap]

The leading edge of the cone gets flattened and it becomes hard to seat a cap on it.

Does the nipple appear to be a hard stainless steel or just blued?
If it's not, maybe a stainless one will stand up to more abuse.
The Ampco alloy nipples may be even tougher than stainless steel!

 

[RSVP2RIP]

Ampco, stainless and blued all have the same thing happen to them.