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…