Need drum thread help!

I pretty much have my Vincent riffle done, so I took it out yesterday and shot a few rounds through it and it did alright. When I started to clean it, I had water squirting out from between the barrel and the drum. I removed the drum and it is real loose in the barrel. Everything came from TOTW including the new taps. I took the drum and screwed it into a 5/16-24 nut and it fit fine, however when I tried running the tap into the nut the tap was to big to screw into the nut. The tap measures .317 on the outside of the threads and the drum measures .306, so the barrel threads are .011 bigger than the drum threads. I never thought about measuring everything before drilling and taping, since everything was new. Do you guys know of any way to save this, or is it a lost cause? I would hate to have to buy a new barrel and start over!

You may find someone to make a new drum for you.. That would be easier. I imagine that you could get any machine shop to make one.

It sounds to me like the wrong tap was shipped, maybe even a metric size? My suggestion would be to get a 3/8" 24tpi drum and tap. Should be an easy fix, other than the positioning of the nipple. Try the tap in a 3/8-24 nut, that may be the tap that was sent.

It should say on the tap what the size & thread is.

The taps have 5/16-24 stamped right on them. Is there any custom builders on here that make their own drums? I have a split dye, I could cut oversized 5/16-24 threads but I haven't been able to find a drum that didn't already have the threads cut.

I'm not so sure that there's anything wrong with your tap, at least diameter wise. I just measured a couple of mine, and one was .316", and the other was .317". If you were to measure a bolt, it would be somewhat undersized. That's the way they are.
What size drill did you use? Did you use lots of oil? How does a bolt fit in the tapped hole? Are you sure it's not a metric drum?
Just throwing out some things to think about.

The drill bit was 17/64, it measured .269. I have a 5/16-24 bolt and it is the same size as the drum threads and fits the same in the barrel. Both the bolt and the drum fit real well in a 5/16-24 nut, but the tap is just a little to big to go through the same nut.

It sure is sounding like you have an M8 x 1.0 tap, which would have 25.4 TPI. A 5/16 x 24 bolt will screw in about 5/8 to 3/4 inch before the threads bind, drumb threads aren't that long. My new M8 x 1.0 tap in the garage measures .318. Double check the markings on the tap.

Don't panic. Easy fix. Locate a half inch ball bearing and set over top of the drum hole on the barrel, give it a rap with a ballpeen and try screwing in the drum again. You have now compressed the treads enough to make it work. In the future always mic the drum and the drill bit prior to drilling. Oh and invest in a thread gauge.

Although swaging the threads at the mouth of the hole might reduce the threads I don't think that would be recommended seeing as these threads must resist internal pressures of up to 18,000 PSI to be safe.

It does sound like a M8 X1.0mm tap was used in making the threads.
The safest way to fix this would be to have a local machine shop reproduce your drum with M8 X 1.0mm threads.

As this may cost a bit at the current high prices of a machine shop I recommend that a new M8 X 1.0 bolt be purchased at the local auto parts or hardware store and try it in the barrel.
If it screws in fairly snuggly, your on the right track to getting your gun fixed.
It sure beats having to buy a new barrel.

Take a thread gauge & check the tap. It could be marked wrong & be a metric tap even to it is stamped otherwise. :hmm:

No way would I try to compress the threads on the outside to try to tighten it up. :shake: We are talking about WAY to much pressure to let 1 compressed thread hold it. The drum threads need to fit the hole threads cut, even if you have to have a new drum made. If that is what you need done, you can buy blank drums & take it to a machine shop & have them cut a metric thread on it, should it turn out to be metric. Or if it is slightly oversize, they can possibly do that as well.

Safty first. I agree.

I bought a 8m x 1.0mm bolt today and tried it. It is tighter than the 5/16-24 bolt, but it will only screw in 1/4 inch before it binds up, however a 1/4 inch is all the further it needs to go in. Would cutting the metric thread on a drum be better than trying to cut a slightly oversized 5/16-24 with a split die?

I just checked the tap that I used and it is 24 thread. Would the metric die still be better to use?

The threads on the drum are undersize. The tap is ok. The tap should not go thru a common nut (unless the nut is oversize). The threaded portion of the drum should mic around .308/.311 if it is good. As others have said, do not swage the threads, this is dangerous. There are probably several gunsmiths near you that could help (I know of one in SW Ohio).

LGK