Pipe/taper thread on rifle barrel?

[dakota.potts]

The other day at work, while running and deburring some 200 valve coupling adapter parts and running thread gages through them, I had some time to think. The parts were threaded NPT (National Pipe Thread). I noticed that properly fitting pipe threads will get tight not just when they hit the shoulder as standard threads do, but as the thread size tapers. Properly sized pipe threads seem like they would add additional security to a muzzle attachment, especially in combination with something like a ratcheting nut system.

I'm not aware of any ever being tried on a firearm. Have they been? Is there a reason they haven't been, or something I'm missing that would make them unsuitable?

Just a dull point of curiosity I had during my shift the other night.

 

[fourbore]

First, EXTREMELY, difficult to headspace without a shoulder to stop on and without a shoulder very hard to get the right torque with a taper thread. A skill machinst can do anything, but this would be a colossal waste of time for anything but perhaps a muzzle loader or some other odd application that only the internet could conjure up.

Second and the first is enough, you would never get the barrel back on the same depth if you had to removed it.

Ah, you refer to flash supressor, yea - that could work a little. Brakes might work also, but would have to get that extra 1/4 to 3/4 turn for alignment. In that case though, there would be a tendancy to compress the bore. All these 'cool' rambo like attachments are already an accuracy liability if not very concentric. And each time the attachment was swapped the threads get squeezed down more and possible constriction of the bore worsen.

Probably not a good idea. You ever take old iron steam fittings apart? Lots of heat or a big hammer!

Interesting to hear other opinions.

Edit: I just remember the muzzle attachments need the shoulder for a square reference, so anther problem to over come with taper muzzle thread.

 

[Gunplummer]

Your "average" pipe thread does not seal the whole length equally. You can taper the bore to match the taper on the thread, but most small internal pipe threads are made with a straight drill. Even when you taper the hole to be threaded, some where the thread is not holding with the same force. Pipe threads rattle down until they hit a tight spot. If the threads fit perfectly, they would never bottom out.
Who knows. If all they had to deal with was pipe threads when guns started out, maybe. I have often thought that threads were a problem when machining started out. You can see on guns how threads progressed as the guns got newer. Older guns have screws so course they look like wood screws.

 

[James K]

Tapered pipe threads need not be very precise, since they are simply screwed in until they stop. Rifle design demands more precision. Further, rifle barrels are often made and threaded before ever being put on a gun, with other features, like gas cylinder attachments being put on based on the thread start. That kind of precision is not usable with NPT.

Jim

 

[tobnpr]

In addition to the points made above, most brakes need to be timed to the barrel- which means you need a shoulder for that. But I've never cut NPT threads, so perhaps there's a practical way to cut them so that the brake indexes precisely when torqued into place...which is what's required.

Crush washers, or lock nuts wouldn't be applicable here either- and outside of a factory threaded barrel usually aren't used.

I have no idea what you're referring to as a "ratcheting nut system"- perhaps I know it by different terminology.

 

[Mobuck]

There was type of foreign made military rifle that used a sort of tapered thread but had a big shoulder that pulled up against the front action ring helping alignment. Not popular or long lived design.
I think if you really get into design. strength, and stress, you will find the tapered pipe type thread isn't as strong as parallel cut threads. Plus, the fine parallel threads provide much more mechanical advantage for tightening than course taper threads.

 

[Scorch]

S&W used tapered threads on revolver barrels for a few years, now they have gone back to straight threads. Seems everybody thinks being sloppy is a good idea until after they get into it and see the unintended results.