2015
10.22

It’s no secret that I have a penchant for oddball guns, be they paintball marker or firearm.  Seeing a design that’s off the beaten path is always enjoyable, be it for mechanical ingenuity or sheer impractical novelty (though usually a peculiar blend of both).  During a recent visit to my friendly local FFL (always good for a rousing discussion and perhaps lightening of my wallet) a friend and I perused a distributor’s sale flyer and immediately spotted an intriguing item – a 12ga shotgun upper for AR-10 lowers.

For those unfamiliar with the AR-10, it is the bigger, older brother to the AR-15 rifle.  In fact, much of what was considered new or novel at the time of the AR-15’s introduction is properly credited to the earlier AR-10 design.  Unfortunately, there is far less standardization on the AR-10 platform than there is on the AR-15.  Eugene Stoner actually updated his AR-10 design decades later to have much greater commonality with AR-15 parts (resulting in the KAC SR-25), while Armalite (not the original Armalite that actually developed the AR-10, just somebody who bought the name and rights) developed the AR-10B using an upper from an SR-25, and somehow DPMS came up with a mashup of these designs, and then…  …yeah, I don’t really understand it all either.  We’re left with saying ‘AR-10′ as a generic terminology for something that looks like an AR-15 but fires a .308 round – as someone once wryly observed, “there’s an XKCD for everything“.

The important part is that the modularity of the AR-15 and AR-10 allows different upper receivers to be mounted to a common lower receiver (which is, as I’ve noted in previous posts, the one part that is itself considered the ‘firearm’ under US law).  While the AR-15 is far more standardized than the various AR-10 incarnations, the magazine well of the AR-15 limits what ammunition can easily be fed through it.  In fact, this limitation has been the underlying factor in the development of various new cartridges such as the .50 Beowulf, 6.8 SPC, .458 SOCOM, etc.  Although a 12ga shotshell by itself will just barely slip through the magwell of an AR-15 lower receiver, designing a practical magazine to feed that ammunition through said magwell is out of the question.  So, the next best thing is to scale up to the larger AR-10 lower receiver.

The ever-popular Magpul .308 magazines will happily accept a standard 12 gauge shotgun shell (extracting said shell is another matter, though).  The rimmed base of the venerable shotshell does not lend itself well to use in a box style magazine (as opposed to the tubular magazine that most traditional shotguns use).  As an aside, this issue isn’t unique to shotshells.  The rimmed base of the famous .44 Magnum round (feel free to insert your favorite Dirty Harry quote here) has limited its use in semiautomatic handguns to only 2 models in history, as far as I am aware – the iconic Desert Eagle, and Emilio Ghisoni’s masterpiece, the Model 6 Unica.

The designers of Kalashnikov derived shotguns (such as the Saiga-12 and Vepr-12) use special magazines with a fairly severe feed angle to improve reliability when stripping and chambering a round.  Unfortunately, that doesn’t translate terribly well to using a straight magwell and magazines designed for rimless ammunition.  The designers of the RAS-12 opted for a pretty radical approach to this problem – they designed their own ammunition.  Which is probably why I managed to snag this very interesting upper for less than a sixth of its original retail price – not much more than 2 years after announcing the product, the company doesn’t seem to be in business anymore.  I may write more on this later, but I’ll limit myself to covering just the ammunition in this post.

The ammunition comes in boxes of 5, with 20 boxes to a case.

The cartridges look very little like a traditional shotshell, and very much like a modern rebated rim pistol cartridge.  In this manner, it is reminiscent of the .50 Beowulf cartridge designed for the AR-15 platform.  The rounded nose and rebated rim makes feeding far simpler than with a standard 12ga shotshell, and allows for easy adaptation of existing magazines.

The most significant feature of the cartridges is obvious – they are not of metal construction, but polymer (US patent 9109850 calls out polycarbonate and nylon as suitable materials, though various online sources specifically note polycarbonate as the hull).  This feature alone is what made me take notice of the system, given that I’ve done a bit of tinkering with 3D printed polymers in gunsmithing applications.  Even if supplies of the original ammunition dry up *cough* Gyrojet *cough* Dardick *cough* EtronX *cough* it should still be possible to recreate the cartridges in a reverse-engineered fashion.  I’m somewhat surprised that the RAS-12 designers didn’t opt to ‘open source’ the design, as SAAMI standardization is precisely what has allowed previously proprietary cartridges to survive in the market if not outright flourish.

I carefully disassembled a cartridge to determine the weights (in grains) for all of the components:

  • Projectile half: 512.4 gr
    • Nosecone: 24.8 gr
    • Nine pellets of 00 buckshot: 481.2 gr
    • Wadding: 6.4 gr
  • Propellant half: 191.0 gr
    • Nitro card: 13.0 gr
    • Gas seal: 17.0 gr
    • Powder: 29.0 gr
    • Hull: 117.2 gr
    • Primer: 14.8 gr

…for a grand total of 703.4 grains for a fully assembled cartridge.  There’s certainly a bit of tolerance to these measurements, but they should serve as a suitable starting point for weights.  Now, to start measuring the hull and nosecone to draw up in CAD…

15 comments so far

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  1. Very interesting concept. I had never heard of it before, although I follow numerous gun related channels on YouTube (AR-10s aren’t exactly common over here in Germany, thanks to our rather restrictive gun laws). Looking forward to updates on your reverse engineering process.

  2. I’ve been tinkering using 50 bmg as the shotshell. So mainly all ya needa source is the nose cone. I was thinkin a plastic Easter egg, for lack of an easier setup.

    I love the concept, they just didn’t go about it correctly. Give away the Ammo, etc

    • How much luck have you had with the .50BMG cases? I kind of discarded that idea due to the base on the .50 being around .046″ smaller in diameter than the base of the RAS-12. Are you fire forming the brass in some manner?

  3. Yep fire formed in 12 ga after annealing. Then used a lathe to turn down the rim to where the ras bolt will grab it. Gettin s bulge about 1/3 up 50bmg, but that brass is so thick I’m not sure it’ll matter.

    Where can we find nose cones for these things? I’m thinkin model rockets or somethin?

    • Interesting, I guess I’ll have to give using .50 BMG brass some more consideration (though I have zero actual experience with annealing, fire-forming, or actual reloading at this point, so I’m still firmly in the ‘research’ stage).

      It’s been a long time since I’ve done any model rocketry, but nosecones of that size were generally balsa – in the years since, I assume injection molded ones have become more popular, though. Unless you could buy in bulk, they may not be terribly cost effective, however. Vacuum forming would be great, but I don’t know if the draw would be too deep (especially when doing multiples per sheet). I’m also wondering how critical the material selection is for the nosecone – hopefully styrene would suffice. A friend is considering injection molding, but the cycle time is fairly long for small scale production. I’d love to know what became of the original molds…

  4. well, i am in contact with an engineer type that had a hand in the refinement of this thing… you can find him on youtube under “direct impingement ar10 shotgun” or something real close to that. he answers questions via email and seems to know alot about the goings on… like i said, will answer questions and very forthcoming, good guy!

    now as far as nose cones, the original moulds are allegedly still in existence, and we are trying to coordinate a group buy of around 10k of nose cones AND hulls. there is allegedly a gen 2 hull that will hold 11pellets and take higher pressures….

    i think this thing still has life, once folks stop being broke from the obama-nomics…

    the uppers at 300 are just too cheap to pass up!

    i ran some more 730 round balls outta mine the other day with 50 bmg hull and the piston pushed the quadrail fwd as i didnt secure the quad rail tight enough to the receiver. and posssibly since i had sized the brass down there was too much expansion.

    also, there is a face book group put on by the guy i mentioned earlier trying to get a group buy of hulls/cones together. he has a link to a guy that will make followers (3D printer ) so taht you can feed rhe ammo without the nose cone…

    s

    • Yes, I definitely came across the youtube video of the DI RAS-12 – lots of useful info in the comments. My plan for one of the next blog posts is to look at the magazine and follower, and hopefully model up the follower in CAD so I can print a few (and then share the files, naturally).

      I don’t use Facebook, but a friend and I would be very interested in getting in on that group buy of hulls and nose cones! Beats making our own molds…

  5. I’ll post a link to the guy who 3D prints followers for use with no nose cone loafings (greater angle to them?)

    • Salty could you post that link? I am working on both 3D printing the round and using 50 bmg as the parent case for fire forming additional rounds.

  6. I have one also, and am thinking of a few projects it would lend itself to: a sniper rifle using a .338 or .416 bullet in the shortened 50 BMG case (a wildcat obviously), or a “firearm” like the Black Aces Tactical DT (26 inches long, pistol brace), using the original ammo.
    We should keep ourselves updated about what people are doing with these.

  7. What is the progress of this inquiry? I purchased a RAS-12 upper and have a lot of experience with drawing CAD down to the minor details, as well as experience in plastic injection molding.

    I would love to put my efforts into getting the ammo being made.
    This is an amazing rifle and I would hate to see this go to waste. CA just ran into some major snags with the latest additions of Gun Control laws that were signed.

    This gun is still legal as far as I can tell since it is a “shotgun” and not an AR.

    • I haven’t had a chance to do anything else since this post – plenty of other things keeping me busy. My local FFL (who procured the RAS-12 upper and ammo for me) has contact with a patent lawyer in the firearms industry, so I asked him to inquire with the lawyer on if there was any word on who actually ‘owned’ the RAS-12 IP, including the molds for the shells. Haven’t heard anything yet, but someone somewhere has got to know where the stuff lives…

      Regarding reverse engineering the hull, my plan was to fill the empty hull with an epoxy/talc mix, then machine half away, flatbed scan the section, drop it into Solidworks, and trace it out. I’ve also been wondering if turning brass hulls might actually be the way to go – a two-part design that uses a base made from solid stock and a ‘body’ made from tubing might work, and should (theoretically) last indefinitely.

      Very interesting observation regarding the CA ‘gunpocalypse’ – I had not considered that. It would almost be worthwhile for someone to make .410 uppers (would need to be 2″ shells, or a custom cartridge, probably) for the AR-15 in that case.

  8. well, since back then havent tried much, howerver just picked up another upper off gunbroker to have as a “spare” or a chinese blueprint….

    also, the bolt face is basically a 20 ga, maybe a new extra would have to be made, but a 20 ga retrofit wouldnt be hard i dont feel

    also what i have tried, and it has worked, was RTVed some buckshot into the 50bmg cut down. so, had full payload, around an ounce, then just mounded glue over top so would get some back pressure…

    the other thing we could do is get the correct dia of the shell formed into a single slug, and that would serve as nose cone….

    still lotsa possibilitie!!!

  9. heres a vid of my first try… i uploaded some others as well, so just scroll through..

    https://youtu.be/M-zaJU6sHSg

  10. youtu.be/IzHAKnLPcBo another try