Percussion Lock - how much metal needed at bolster

[galamb]

I am working with a Chambers Golden Age percussion lock which will receive a 1/2" drum.

The (cast) cut-out for the drum does need to be cleaned up a bit with a file, but would like to know how much metal I should leave - so how deep can I go reasonably without jeopardizing the integrity since the main spring is supported there.

As it is right now there is about .14" of metal left at the lowest point on the drum cut-out - could I take it down to .125 or .100" safely?

[T*O*F]

The question I would ask is what diameter is the lock cut out for?  If it's also 1/2" then chances are you won't have to deepen it, only clean up the sides for it to fit.

[Mark Elliott]

If you have the right size drum,  you shouldn't have to take any significant metal off.    The drum needs to fit tight up against the lock plate for support.   Otherwise,  the hammer will eventually break the drum off.   

[Acer Saccharum]

Well, you can deepen it, but make sure you can still get the hammer to center on the nipple. Or you might have to bend the hammer for best orientation later on. Watch your front lock bolt location. If you raise the lock, you might not be able to use a front lock bolt. Many perc guns didn't.

As far as 'why' lowering the drum, this would help make a thinner gun, I can see that.

As Mark sez, you do want to make sure the drum is supported by the plate. This will help in the long term stability of the drum. The plate will add considerable mass behind the drum, so the threads don't take all the stress of the impact. Without support, the drum will loosen, and mis-alignment occurs, shimming, teflon tape, loc-tite, and a litany of ills that plague the percussion system.

A well made drum and nipple arrangement will cause no problems in itself. Make sure: 1) the drum is a good fit to the plate, and 2) DON'T take the drum out for cleaning the rifle. That only wears and stretches the threads, and causes the nipple to go out of alignment with the hammer.

[galamb]

Thank you for the responses.

The lock is cut for a 1/2" drum.

I'm having a bit of a geometry issue during my layout due to using an Allen drum style patent breech. So I have no worries about snapping the drum off - it's cast right into the breech plug with an additional shoulder on the top of the drum which is tapped for the nipple - figure I would more likely break a hammer before snapping the drum off.

And that in itself is part of the issue - the nipple is sitting a little higher than it would with a standard 1/2" drum screwed into the barrel due to the casting.

I can trim down the shoulder on the casting itself and gain a little without having the nipple threads extend into the flash channel, but if I can also take down the cut-out in the plate by .02-.03" that can mean the difference between using a short pistol nipple and a more standard rifle nipple.

My other alternative is to replace the hammer to one with a bit more throw, but before going that route I would like to try and trim a bit here/there where I can if possible.

[Acer Saccharum]

I'd cut the plate down as low as I could. You can also file some off the bottom of the breech snail. Just don't break into the flash channel.

[galamb]

Ok thanks,

my biggest concern was leaving enough in the bolster to support the mainspring.

There is so much "meat" around the cast drum/breech, that I could take that down a tad without jeopardizing any of it's strength for sure.

This is significantly more challenging than simply placing the lock, drilling the hole for the drum or touch hole and going to it - it gives you zero "wiggle room", but it has been a great learning experience so far.

Would not recommend this style of breech for a first build - could cause all but the most stubborn to abandon the project 

[Acer Saccharum]

Galamb, just work at it slowly and thoughtfully. Don't get yourself in a rush, or try to force it. You'll do fine.

Tom

[Pete G.]

Most of these things fall into the category of "a little here; a little there", maybe with a couple of sleeps in between. Study the problem and think about it before you just dive right in. You will probably like the end result better.

[galamb]

Yes, thanks Pete (and Tom).

I have been horsing around with this for a month or so off and on.

I asked a while back about using shorter profile nipples with the combo I selected.

So I have been taking this one very slowly (have something on the bench right now, but it's almost finished and have been "visiting" the lock/breech off and on in between).

This is one of those cases where I simply want to make a specific lock work with a specific breech system that was not exactly designed to work together.

The breech would work fine with a 1.75" throw hammer with a bit of fine tuning. The lock "I" want to use has a 1.65" throw so I could make it work by using "snake eye" pistol nipples by taking down the shoulder on the drum a touch.

If I take the shoulder down a touch more (and there is lot's of meat there so the nipple threads will not interfere with the flash channel) I can "almost" get a (standard) pistol length/short rifle nipple to fit (which are easier to acquire for me).

When I got pidding with it the other day I noticed that if I could drop the drum cutout in the lock plate by another couple hundred's of an inch a standard rifle nipple would probably fit or at the very least, if using the standard pistol nipple the geometry with the hammer would be almost bang on without having to bend it much if any.

If I wasn't so stubborn (trying to see if I can get it to fit), I would have simply replaced the hammer or gone with a Hawken style flint breech and installed the drum where it wanted to go (I only build with patent style breeches - just a personal quirk).

But when I saw the two separate parts, I just "wanted" both and am determined to get them to work together without compromising the integrity of either (just probably never again)  

[Acer Saccharum]

Graham, once you get everything fit just so, you need to fit the hammer face to the nipple.  Put some Prussian blue on the nipple, and lower the hammer to pick up the blue. Grind that away, and repeat until you have a nice even contact all the way around.

A Dremel running a carbide burr with a teeth cut on the end will suffice very nice.

Tom

[galamb]

Thanks Tom,

I have that part down. Have built two with snail breeches which I had always read were the most difficult to get the geometry correct - my opinion has changed 

I have been working on the breech today, taken down a fair bit of the shoulder on the drum (and still could go more without the nipple threads even coming flush with the outer edge of the flash channel).

I am almost happy with it now, mostly just want to blend all the edges so it looks nice and pretty, and the geometry is good with a short nipple from Thompson Center - debating whether to go further and see if I can get a regular rifle nipple to fit - it looks like it might (but perhaps leave well enough alone).

The hammer will need a little tweaking and a slight bend inboard, but I am now confident that it's going to work out nicely without having to replace the hammer.

Perhaps I will reconsider never using this style of breech again 

Do really appreciate all the advice/assistance, I'm still a little leery about removing metal from the breech area but am gaining confidence (and nothing has gone boom the wrong way on me yet).