How are pistol barrels made?


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Brass Fetcher
May 19, 2006, 07:02 PM
I am looking to fabricate my own .32NAA barrel for a Kel-Tec P3AT, as I cannot find a company so far who is willing to take the job.

Here is what I have:

A full machineshop w/machinists
I'm a mechanical engineer
.32 cal barrel blank
.32NAA reamer
Kel-Tec P3AT

Here's what we don't know:

Are pistol barrels generally heat-treated in any areas?
Are jigs typically required and if so, what is a good time estimate for a one-off semi-auto barrel?

Thank you very much.

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Vern Humphrey
May 19, 2006, 07:53 PM
Are pistol barrels generally heat-treated in any areas?

Most modern pistol barrels are heat treated.

Are jigs typically required and if so, what is a good time estimate for a one-off semi-auto barrel?

A semi-auto barrel consists of three prime elements:


The barrel proper

The locking lugs

The lug or cam which locks and unlocks the gun.


Probably most barrels are forged, to leave the steel for machining the lugs and cam. It is possible to make lugs and cam separately, and slip on and silver solder this assembly to the barrel.

The barrel has:


The chamber (and you'll need a chamber reamer for this -- and a headspace gauge)

The rifling. You can make a rifling cutter and rifling lathe -- but now you're into real work
.

Wilson 17&26
May 19, 2006, 08:47 PM
One of the few .32NAA barrels (only fit the First-Generation P-3AT) manufactured by Kel-Tec was sold earlier this month for $206. Two other Kel-Tec .32 NAA conversions were sold last year at lesser amounts. Itís sad that only 10 of these conversions were put into public hands.

brickeyee
May 19, 2006, 09:32 PM
The rifling is actually the hardest part.
Most pistol barrels have been broach or button rifled for a while.
A few are EDM.
Elechtrochemical rifling has been making inroads recently also.

Jim Watson
May 19, 2006, 09:40 PM
Barrels are not generally heat treated after manufacture. If you are making one out of a blank of decent quality it has been drilled, reamed, rifled, and stress relieved from a bar of the desired hardness to start with.

I am not a mechanical engineer nor a machinist. That said, you don't necessarily have to have purpose made jigs, but you have to fixture the blank in the machine tools somehow.
Time required is longer than you think to reverse engineer and one-off something like an autopistol barrel. Maybe you could monobloc the chamber end of a factory barrel with a tube from your blank; if there is enough meat there to allow chambering for the bottleneck.

Brass Fetcher
May 19, 2006, 11:27 PM
Thanks for the responses ...

Jim Watson, what do you mean by monobloc? I thought about having the barrel sleeved and welding a .380ACP dimensionsed protrusion to the chamber end of the sleeve - and then going in and reaming with the .32NAA reamer.

Wilson 17&26, can you advise where these barrels were/are sold and a price figure?

Thanks all.

Jim Watson
May 19, 2006, 11:57 PM
By monobloc, I mean to take the factory barrel, and cut the tube off in front of the locking surfaces, ream out the chamber section as big as you could. Then turn the .32 barrel blank to fit into the breech section at the rear and to the standard diameter at the front. Then screw, glue, or solder it into the breech section. That is the way Springfield Armory .45 barrels, Browning High Power 9mm barrels, and a whole host of shotgun barrels are made.

Chamber for .32 NAA. If, if, IF there is enough metal thickness there to make the joint and hold the chamber pressure. But you are the mechanical engineer and I am sure I don't have to explain that to you.

There is not much welding done on gun barrels, it distorts things. Most of the two-piece jobs are furnace brazed, as I understand it.

RyanM
May 20, 2006, 01:47 AM
Here's a small bit about how Kahr makes barrels. http://www.kahr.com/vg_barrel.html

It seems very odd that they drill a hole through the middle of a giant round piece of steel, rather than starting with a small, flat bar that's closer to the final dimensions. I guess they must have some reason.

Sylvan-Forge
May 20, 2006, 03:03 AM
Neat pic on the kahr site ..

Maybe the big ole round blank shown only comes in a few basic sizes from the foundry ...

I've been looking a little bit into doing a .32naa for the sig p232. Of course it's blowback, hopefully easier than a locking.

From what I gather (which isn't much), the overall heat-treating has already taken place on the blank, as Jim has mentioned.
Any info on the blank maker?

Locking and contact areas/surfaces ... Not really sure ... a good finish probably most important ...

chamber and barrel structure ... ?
For a common barrel, I'd think the overall treatment for hardness, especially if from a good blank, would allow you to just (heh) measure and cut/ream/machine.

I know I'll be looking for cracks and stress obsessively, since I'm neither a machinist nor an engineer.

Best of luck JE223!

Powderman
May 20, 2006, 03:14 AM
Assuming a barrel I.D. of .311, you can order a barrel blank from most major barrel makers. Douglas and Shilen come to mind for pistol barrel blanks with the proper twist and rifling.

Once acquired, it should be relatively easy to turn down to the proper diameter, and to cut locking and/or barrel lugs, hood and outer chamber.

You should be able to chamber the barrel easily; contact Brownell's for the proper chambering and finish reamers. If they don't have them, you can special order them, or contact Clymer's for reamers. Some gunsmith machine supply shops will actually allow you to rent the reamers for a small fee, rather than purchasing them outright. Good luck!

ugaarguy
May 20, 2006, 04:39 AM
JE223, Let us know how this works out. I supect that many folks here at THR and over at www.ktog.org would be interested in 32 NAA Bbls for their P-3ATs, myself included.

Third_Rail
May 20, 2006, 10:45 AM
After machining the outside to the correct profile (to include lugs and soforth), chamber it in a lathe. Ta-da.

Barrels aren't too complicated, thankfully. Only the rifling part is. :)

brickeyee
May 20, 2006, 10:51 AM
"It seems very odd that they drill a hole through the middle of a giant round piece of steel, rather than starting with a small, flat bar that's closer to the final dimensions. I guess they must have some reason."

Ever tried to drill a perfetly straight deep hole in metal?
It is actaully a relatively tough thing to do. It takes a spceialy designed bit that does not tend to wander. Any variation in the hardness of the metal from grain changes tends to pull the bit off center.
A perfectly uniform blank is required of there is any hope of getting a stright hole.
Look up 'gun drilling' and you can see the bits used and maybe some ofthe equipment.
The large manufacturers have often switched to hammer forging since it does not require nearly as deep a hole. A short squat blank is stretched to the final barrel length while being hammered uniformly on the outside over a mandrel that is a mirror image of the rifling desired.

numbertwentynine
May 22, 2006, 04:39 PM
you start with a round blank instead of a bar so that you can put it in a lathe witch is far more capable of making concentric holes than a milling machine is. Also the metal hardness in the center of a piece of round bar is unform around the ceter axis whereas in a bar it would not be.

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