replacing an antique drum with worn threads?

[DavidC]

I just picked up an antique percussion rifle and was disappointed to find the drum extremely loose. It looks like the drum threads are crushed and the threads in the barrel are worn. This is my first percussion gun so I'm not familiar with my repair options. You can see the drum was positioned right up against the breech plug so it may be troublesome to drill out and replace the drum with either a larger thread or with a bushing to downside the thread.

I could use some guidance. I'm intending to shoot this old girl and get her back on the range. Aside from gunk the rest of the gun looks very good. I suspect some jackass tried to bubba his way through a repair or over torqued the drum. How can I best fix their error?

Thank you!
Dave

[Bob Roller]

  It looks like a bad job from what I can see. WHAT is the diameter of the threads on the drum? The nipple looks to be angled as well.
  You might try a 3/8x24 tap and see if it will clean up the hole and get a NEW 3/8x24 drum and see if it will tighten firmly
  and if the nipple will line up with the hammer.Getting a rusted old gun back to use can be a job and can be more work than is obvious here.
  Bob Roller

[rich pierce]

Bob is on track as usual. It’s very common on old percussion rifles for the drum to be partway into the breechplug. On most the drum must be removed to unbreech the barrel. In a case like this it’s going to be hard to retain any patina on the side of the barrel and do a good job, as the barrel side flat should be leveled before proceeding so you have a good surface to tighten against.

[kutter]

I would use whatever Tap Drill size would just clean up the old drum threads.
Doesn't matter if it's a Metric or US thread. Just trying to leave the max amt of metal and take away the least amt.
Then Tap the hole with the appropriate Tap.

While it's set up for the above drilling & tapping,  lightly face the hole with an end mill cutter to give it a bearing surface for the new drum.



Since the orig drum apprears to have needed some adjustment in the placement of the nipple,
a new drum being made just for this rifle can easily be fashioned and at the same time the nipple seat cut in at the right location and angle.

An already threaded fastener can sometimes serve as the starting point for making a drum but turning and threading a piece of stock will get you much better thread fit.

Of course a commercial replacement drum could also fit. They are made in many sizes and threads.
Make sure the OD of the drum fits the cut out on the lock plate as well.

[Bob Roller]

A 7/16x20 would probably work.The cut in the lock plate for the drum might allow a 9/16 diameter drum with the 7/16x20 thread.
The nearest metric size is 11MM and unless you have metric taps and dies and drills the US standard is the best choice.
7/16 is .4375 and 11MM is .4334.
Bob Roller

[bulljg]

You could measure the thread and get a "oversized" tap. I believe they are made +1 and +2 oversized. Try searching McMaster Carr. I think they also recommend the tap drill size to match.

[Goo]

I had this problem on a repair job for someone In my case the breech plug was missing so I shortened the barrel by 1 inch.  Another problem is with the many of the new replacement drums. Who ever is manufacturing them cuts  a relief at the thread base and the threads end up being missing so you end up making a drum too.   

[kutter]

You should be able to see if the face of the plug is backed off from the hole now or right even with it.
A simple bent wire pick can also reveal alot.

If the new tap drill size clears it all the better.
If the new tap drill size is going to end up hitting the face of the plug,,then stop the depth of that tap drill as it just clears the bbl wall.

That will avoid the drill being pushed towards the muzzle and enlarging the dia of the hole.
Then tap it in the same set up (drill press/mill) using a starter tap w/a shotened nose. Then finish with an end tap to carefully cut the thread  to the bottom of the hole.

I'd go ahead and make a drum so you can cut the threads for a better fit than the usual Off the Shelf stuff

[Gaeckle]

You should be able to see if the face of the plug is backed off from the hole now or right even with it.
A simple bent wire pick can also reveal alot.

If the new tap drill size clears it all the better.
If the new tap drill size is going to end up hitting the face of the plug,,then stop the depth of that tap drill as it just clears the bbl wall.

That will avoid the drill being pushed towards the muzzle and enlarging the dia of the hole.
Then tap it in the same set up (drill press/mill) using a starter tap w/a shotened nose. Then finish with an end tap to carefully cut the thread  to the bottom of the hole.

I'd go ahead and make a drum so you can cut the threads for a better fit than the usual Off the Shelf stuff

I think this is the best way to fix this. If you remove the breech plug it will re-index in a different position, a new problem opens up and then more fun begins.

[DavidC]

I've cleaned the inside of the hole up a bit with emery cloth and it's measuring around .370-.375 . Right now I'm leaning toward a 7/16 - 14 tap since the tap drill size for a letter U drill is .368. But, since I'm not a big percussion guy, will that thread work? This is a .36 cal target gun and the barrel wall thickness is about .312. I figure I should be able to get 3.5-4 full threads of engagement which would be, I'm hoping, sufficient for use.

Any thoughts on that? I'm hesitant to move up into the finer thread (7/16-20) because the tap drill size moves up about .4mm and the .2mm shift of the hole would move me beyond the barrel flat. At least the steel(?) is somewhat soft but not coarse like A36. Remington steel this barrel ain't

[rich pierce]

DGB, what do you say?

[DavidC]

DGB?

[rich pierce]

DGB?

DGB is a machinist friend who has done dozens of jobs like this.

It seems like the proposed threading will be fine if the side flat is wide enough.

[DavidC]

Ok. Could you tell me what information or resource you guys use when contemplating threads for drum size of different caliber guns? I'm assuming there's some concern about the load and pressure being too much for a tiny thread. I'm betting 1/4-28 is not the best thread for a drum on a .74 cal military conversion, for example.

[rich pierce]

Several factors come into play. All drums should be well supported by a lockplate or the continued striking of the nipple stresses the threads. The smaller the threaded portion, the weaker the resistance to these sideways blows.

It’s important to have a decent bearing surface of the shoulder on the side flat.

It’s important to have a flash channel that is not tiny.

It’s important to have at least 3 full threads, preferably 5.

I think pressures are always less on big bore guns; partially because few folks load them to 1800 fps or higher velocities.

As long as you work within these parameters there’s a lot of freedom.

Thoughts of others?

[DGB]

The advice from Kutter is good. Keeping the original patina/old look is going to be the deciding factor on how serious you get with the rework. I have saved several barrels in about this condition by cutting barrel off just ahead of the drum threads. This involves a lot of planning and careful measuring.
Then make a new section similar to a store bought patent breech. Install the new breech in the newly threaded barrel and proceed as you would in building a new barrel assembly.
Yes, a lot of exacting math and planning. When doing this, you new to have a good reference point to work from. I have used  the last barrel lug as a point to measure back from.
Done properly, your barrel pins or wedges should still fall back in to the original location.
Good luck,
DGB

[Daryl]

DGB's suggestion sounds good to me. I cannot "see", from a safety standpoint, re-cutting those drum threads already there & ending up with anything I'd want to be around when fired, let alone shooting it myself.

[DGB]

Oops, meant to say "need a good starting point"
DGB

[Dphariss]

Did not read all the posts. If you insist in changing history make sure you make the drum of a good quality HOT ROLLED STEEL. Not cold rolled.  I would leave it alone.
But thats just me.

[shortbarrel]

DGB said it all. Only safe way to do it. Have made this kind of fix on many old guns. Have also made them longer by the same process. If you have the tools, equipment and skill to do this have at it. All the barrels that I did this to were bolted down to a proof shed and fired with many times with large powder charges. Some of the above fixes might work, I only have two eyes and I want to keep them. Am just a 87 year old man that takes safety first when working these old rifles.

[Clark Badgett]

I'm in the leave it alone and shoot a new rifle camp.

[Taylorz1]

Well I feel like an unwashed heathen now but if Ive got a gun with buggered drum threads I just drill out the old threads to the next tap size larger and retap the hole then make a new drum out of tool steel. Half the rifles I have are probably on their third or fourth drums...but I have a lot of junky guns ha. I wouldnt do this on a highly collectable rare gun but on the average shooter grade old percussion gun I dont personally think its a great sin. Most people cant tell its a new drum after I beat on it and rust it up some. If the breech plug is in the way I just square it off with an end mill while Im doing the redrill. I think some of the old dead guys notched the plug with a cold chisel and a strong arm by the looks of some of them.

[rich pierce]

Cutting the barrel off and making the setup DGB outlined also gets rid of a burned out powder chamber, which is common.

[Taylorz1]

If I have a burned out powder chamber or a big rust ring in the barrel at the breech end as often happens if the gun was left loaded I unbreech the gun and use a boring bar on the lathe to clean the breech end up. Then I make a steel sleeve to slide in to create a new powder chamber. You can leave the original breech threads untouched most of the time and can also make the powder chamber whatever volume or shape you want. I just loctite the sleeve in once I refit the breech plug and then re drill and tap for the drum and you have fresh threads cut into a new modern steel sleeve. Everything is done internally this way so the patina on the gun is untouched. If turning the new plug against the flash burned side of the barrel give you heartburn because it doesnt sit perfectly flush you can use an end mill exactly the size of your new drum and the work will be very hard to spot. Just another way to skin a cat.

[rich pierce]

If I have a burned out powder chamber or a big rust ring in the barrel at the breech end as often happens if the gun was left loaded I unbreech the gun and use a boring bar on the lathe to clean the breech end up. Then I make a steel sleeve to slide in to create a new powder chamber. You can leave the original breech threads untouched most of the time and can also make the powder chamber whatever volume or shape you want. I just loctite the sleeve in once I refit the breech plug and then re drill and tap for the drum and you have fresh threads cut into a new modern steel sleeve. Everything is done internally this way so the patina on the gun is untouched. If turning the new plug against the flash burned side of the barrel give you heartburn because it doesnt sit perfectly flush you can use an end mill exactly the size of your new drum and the work will be very hard to spot. Just another way to skin a cat.

Clever approach!