Percussion drum boo-boo

[mongrel]

This is going to be locked as soon as I post it. I'm posting it only for information/educational purposes.

A customer sent me a disassembled CVA Kentucky Rifle kit that had been put together not-too-well by a third party -- I have no idea who. Most of the work done ranged from not-so-good to okay, but at first look everything appeared that the gun would be not only shootable but safe. However....

The customer wants the metal re-stocked in walnut. I gather the gun is a gift for someone. A kid, maybe? Dunno. Doesn't matter. I took on the job and the other evening got the barrel fully-inletted, and prepared to inlet the breechplug tang. The easiest way for me to do this is to first remove the percussion drum, so it's not in the way, and afterwards I will thread the drum back in and notch the stock for it.

It was when I went to unscrew the drum that I had my first "Eh?" moment. I hadn't studied the individual parts of the rifle all that closely, so it was only now that I noticed that the drum is of 7/16" outside diameter. Every last CVA, Traditions, Jukar, or other Spanish-made drum I've ever dealt with has been 1/2" OD. So, I unscrewed it, and the mystery of the odd size was solved. A bigger problem was also revealed, and I am waiting for the customer to reply to my e-mail of explanation before I proceed any further with this project.

This is what happens when someone, missing an original part off a gun, ASSUMES. The assumption, here, was that the hole for the drum was a fine-threaded 3/8", so the assembler of the kit rifle acquired/provided a drum threaded 3/8-24.

The hole in the barrel isn't 3/8", nor are the threads 24 TPI. It's 10x1.25mm, meaning it's both smaller than 3/8" and of a completely different thread pitch than 24-per-inch. Not to be defeated by mere mechanical realities (or, more likely, ASSUMING that the difficulty he had threading the drum in was just due to gunk or burrs in the threads), the would-be gunsmith simply got a larger wrench. Amazingly, the whole shank of the drum threaded in -- these things are made of mild, unhardened steel and most generally they just twist apart when subjected to too much torque.

As you can see, some of the threads of the shank are just plain gone. The others have been sort-of forced to metric configuration, at the same time that the threads in the barrel and breechplug were sort-of-forced to American Fine configuration. The result is that what threads are left are badly-galled, half-stripped, and dangerously compromised.

I know lately it's seemed like a bit of overkill on the don't-fool-with-mechanical-stuff sermons, but this drum was just waiting to become a steel projectile exploding sideways from the rifle. Unfortunately, it wouldn't have been the idiot with the wrench standing alongside it when things let go.

AGAIN. If you don't have the experience to know both that there are a number of similar-sized but very different thread types, and how to determine which it is you're dealing with -- in other words, if you lack the experience to have a good idea what you're doing -- LEAVE IT ALONE. This is the sort of mistake that can very easily kill someone.