Tuesday, February 23, 2021

Random curiosity


I believe that the gun-haters will never stop chipping away at our right to bear arms. I also accept that they will have occasional victories that are hopefully temporary. 

For whatever illogical reasons, they fixate on semi-auto arms.

Since I like options and technical challenges, I wonder what the venerable top-break revolver would look like if chambered in 9mm Luger (a short cartridge) and the design was tweaked to take advantage of modern materials and metal cutting/forming technologies. The benefit of a short cartridge is that the heaviest part of a revolver along its length is the portion that includes the top-strap, cylinder and bottom.

I would be inclined to enlarge and square-off the front of the trigger guard.

What the guts of a revolver look like after removing grips and side panel.

I would maximize net-form and near-net form technologies like precision blanking, powered metallurgy and investment casting. I would avoid some of the precision, mating surfaces by inserting polymer "wipers" to keep grit and grime out of the action.

With Computer Aided Design, it might be possible to use one of the exotic copper alloys like C87900 or C87500 to investment cast the frame. These materials melt at a low enough of a temperature that they can be melted in a kiln used to bake ceramics. 

CAE can guide the designer into where to locally add more beef to minimize stresses and maximize stiffness. It also provides information about where material can be pared out or eliminated and replaced with thin sheet-metal.

I would use the S&W J-Frame guts as the basis of the action. The patents on the J-Frame expired long ago and it is a proven design. Unlike the image shown above, the J-Frame uses a coil spring for the hammer spring.

I wonder what a 2" or 3" model would weigh, how it would feel and what a reasonable MSRP would be.

Of course, if somebody were casting and assembling it in their private workshop then the question of an MSRP is nonsensical.


  1. At what point does it pass the 80% part? And is it possible to do an 80% firearm the same as an AR lower? Captive parts? Or use as much J frame parts as possible? Are such parts still available?
    And the big question is
    FFL requirements for any of it?
    Is a DIY revolver kit something that could go viral?

    1. Many questions I cannot answer. It is conceivable they could lower the 80% number to something lower.

      Just some background information, investment casting is also known as lost-wax process. The desired form is carved of wax or something that disappears with heat (like polystyrene foam).

      For precision work it is dipped in a clay-slurry. The clay has additives to minimize shrinkage, cracking and peeling. After the clay skin is dry, it is buried in a bed of sand with a touch of corn flour and the wax piece (with sprues for molten metal feed and risers to help vent gasses). First dried, then the wax is melted out. Finally, the molten metal is poured in.

      The process is precise enough that fingerprints on the wax pattern can be discerned on the metal casting.

      So, what percentage would you assign the "wax" pattern? Precisely 0% of it ends up in the finished firearm.

      I am just trying to think outside the box and maybe one or two steps ahead of the control freaks.

    2. The trick for making a viable 80% kit is a way to attach and headspace the barrel that is doable for someone with no specialty tools. The AR or glock kits have the precision machining done by the barrel manufacturer. The top break revolver does lend itself to this, where lower part of the frame is the serialized part with the trigger, hammer, and grip. The upper section with the barrel and top strap would be 'not a gun' and could be made and shipped with out getting ffl's involved.

    3. So according to US Code, and the ATF, there is no such item known as "80% receivers." There is only "firearm" or "not firearm." The Firearms Technology Division of the ATF will evaluate individual samples and either say it is or it isn't. The sticky point with kits is they have flip flopped recently, deciding that buying an unfinished receiver in the same kit as the items needed to complete it constituted intent (Polymer 80 BBS kit), thereby making it a firearm by default. Ridiculous, I know, since it isn't illegal to manufacture your own firearm, nor does it require a serial number.

  2. 9MM tends to walk the bullets out of the cases in a revolver if the frame is light enough. I know several folks who have had issues with 9mm revolvers.


    1. Thanks for the heads-up.

      I was thinking a target weight of 20 ounces would be a reasonable first-guess. I don't see this competing with a scandium or alloy framed snubbie for weight.

  3. If squaring the front of the trigger guard is to make a finger rest, I wouldn't do it. You don't want fingers near the cylinder gap. Jerry Miculek demonstrates the proper two-hand revolver grip on the googtube, worth watching.

    1. Thanks for the info. I was thinking of finger-rest but like large trigger guards for gloves.

  4. I am curious about the caliber choice of 9 mm. I would think that .38 special/.357 magnum chambering would be easier for production with a minimum amount of equipment. Head spacing on the rim is simpler to machine vs the case mouth, and designing the ejector for rimmed cases would be easier too. 9 mm is more common now, but if everyone has to switch to revolvers I expect .38 special production to take off.

  5. While the barrel would be the same for a .38 or 9mm, the chambering is different enough that you'd want to make dedicated cylinders for the two different calibers, like the Taurus 692 or Ruger's "Blackhawk Convertible".

    Moon clips solve the 9mm backout problem and provide speedloading.


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