Monolith Arms P-12: The P-90-like Shotgun That Never Was

Back in 2007/08 a company called Monolith Arms was promoting a pump-action 12 gauge shotgun they designed. The shotgun was notable because it fed from a horizontally mounted magazine inspired by the FN P90.  They shotgun was promised to be on sale in 2007, when they did not ship it in 2007 they promised it in 2008, but again it never materialized.



Maybe Monolith Arms were just a little to early to the market. There is a lot of interest in high-capacity shotguns these days, for example the Kel-Tec KSG, and a number of high-capacity solutions for regular shotguns such as the MD-20 drum magazine for the Saiga-12. It would sell well today.


Halo P-12  1237524552055

Back in early 2008 the company released this teaser video of the shotgun …

Many thanks to Jacob for the photos.

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Anonymous

    So what happened to them? Has anyone contacted the designer and asked?

    • Raven

      I’m guessing FN probably invoked patent stuff on them, given that the mag design is practically identical.

      • Jeremy Star

        That was my assumption. You could make some really cool, really high capacity pistols with a horizontal magazine, but FN would probably sue you into non-existence.

        • lolinski

          But can they claim patenttrademarkcopyright if it has been made before?

        • Samuel Suggs

          so this but more compact and with an actual ergonomic grip angle?

          no i do not now what the hell it is although dought its a p90 prototype

      • ShadowHatesYou

        I don’t think this is likely. Though FNH was issued a patent, Springfield Armory beat them to the punch in 1953 with “The Hill” SMG in 9mm.

        The existence of prior art provides a challenge to their patent, so if they ever tried to assert it they would surely lose.

        • Avery

          Oh, oh wow.

          I did not know this thing existed until today. I remember coming up with some thought experiment about how much a Owen’s gun would look and operate if it had an inline magazine and this answers some of that. It’s like hearing about the Mondragon’s helical drum, it’s interesting that these guns were made before.

    • Variance

      Magpul purchased Monolith Arms in 2008 or 2009. Unfortunately, they have yet to release (or in some cases, re-release) and of the products that Monolith had developed as an independent entity.

      • Indeed. Their FS2000 handguard is still sought after and the hope had been Magpul would increase, not cease, production.

      • rjackparis

        God damn magpul, It’s a very clever strategic business move. Just like the aries FMG remake but DO SOMETHING WITH IT. While maybe FN sent them a letter, I’m nearly positive they could have done something with the project.

  • CoCo

    That thing looks like a fair portion of it could be 3D printed. Hint hint.

  • Andrew Malik

    Where are you supposed to place your cheek?

  • Bryan .

    Looks like they have molds… can you say crowdfunding?

  • greasyjohn

    Fake sounds and no footage of it ever firing… it’d be vaporware if anyone was still talking about it.

    • Qaus

      never thought i’d hear “vaporware” outside of videogames/programming, let alone on the firearm blog.

  • DougE

    I looks hideous, but if it worked it could’ve brought a lot gun to a fight. My guess is that all the problems hinged on the magazine. Either from feeding issues or FNH sending a nasty letter via lawyers.
    The video was terrible. The only time we saw the action (in action) was without the magazine, and the context of the shell ejection was very out of place.

  • Nicholas Mew

    The Rim of the Cartridge must have done it in. Not to mention it’s difficulty in extraction.

    • Vermin.308Winchester

      I am sure that it caused some problems the Lack of Any information on feeding issues certainly supports that hypothesis

  • Vermin.308Winchester

    The U.S patent was published in 1990 so it should have expired. The buyout bye Magpul is what makes this interesting that suggests that they had something worth buying whereas all other evidence suggests otherwise its not hard to simply dismiss this as unoriginal non functional garbage especially in lew of that we’ll what’s the right word? Insanely stupid video two words but anyway has Magpul said a peep about the matter or filed any patents? Where the creators lay of or hired on hate to criticize you Steve

  • Vermin.308Winchester

    Think they took a few pointers from the mossberg 500 bullpup

  • AldanFerrox

    Well, this gun needs the rimless RAS-12 ammo from Intrepid Tactical Solutions.

    • TGM

      A modern, rimless shotgun shell is the future of autoloading shotguns but “new” calibers are a very hard sell in the civilian gun market.
      A new rimless shell would have to still be compatible with existing shotguns for it to ever catch on.

      • Mark

        Maybe this is a stupid question, but would it be possible to simply put sleeves on 20 gauge shells to match their rim diameter for feeding autoloaders? It’s a kludgy solution, but it would be a way to transition to a new cartridge design similar to a 12 gauge shells, but optimized for non-tubular magazines.

      • AldanFerrox

        Or if someone manages to sell a weapon with this ammo to a major military buyer. This would be the other option.

      • HSR47

        Realistically, I don’t think we’re going to be seeing a mass-marketed rimless 12 gauge shotgun cartridge anytime soon.

        In order to be mass-marketable and affordable, there would need to be standardization on the supply side, which rarely happens without a military contract of some sort*.

        As far as military contracts go, I can’t see the U.S. military adopting a new rimless shotgun cartridge without a multi-entrant competition, and long-term trials. As far as this goes, I doubt the U.S. military has any interest in such an expenditure at this point in time, and I’d wager that this state of affairs will continue for at least the next half decade.

        *the only recent example I can cite here is .300 BLK, where AAC/Remington took the idea of .300 Whisper, improved it slightly, and standardized it, so that they could then use it to push silencers.

        • Cymond

          And even in the case of the 300 family, it’s not a completely new cartridge. It’s based off a pre-existing cartridge that is already widely available.

          • perlhaqr

            .50 BMG shells cut to length are just about perfect matches for 12 gauge.

          • HSR47

            If I had to guess, I’d say that someone at AAC and/or Remington was playing with .300 Whisper, and convinced their higher-ups of the commercial possibilities of that cartridge with minimal R&D investment.

            Also, the fact that it generally only requires a barrel change to convert from 5.56mm NATO to .300 BLK certainly doesn’t hurt either.

            In terms of a rimless shotgun cartridge, by the time you replaced magazine tubes, shell stops, bolts (or at least extractors), and barrels, you’d probably be better off just buying a new shotgun. Really, the only place I can see it being truly beneficial is with shotguns based on the AR10 and Kalashnikov pattern actions (among others) using box magazines. At that point, the reliance on box magazines would likely require the use of an entirely brass cartridge case in order to counteract the tendency of plastic-hulled shotgun shells to be negatively effected by spring tension (and heat).

          • JumpIf NotZero

            It’s based off two existing cartridges 😉

  • Jacqueshacques

    My favourite part is how the shells in the magazine don’t move when he racks the slide – if you pause the video it doesn’t even appear there’s any kind of magazine spring.

  • jogo69

    This is bullshit not a bullpup…. its just a toy …what’ta homemade video … the actor portraying using the “toy” you suck in your costume….Go play water pistols

  • wpjokari

    FN was going to do a .22lr version of the p90, that’d be my first choice…no way rimmed will work and if it did no one would trust enough to buy it. The real Saiga12 mags have curvature, this has none and all 4 pics omit the rear end/mag spring area while he’s got 20 rounds in there..would have to be beefy/massive. Magpul’s coolest one was the folding glock rig/flashlight combo PTS FPG, but as an SBR, no sales potential.

  • Outbreak

    Why are all the cool shotgun designs only available in pump? I’d love a Keltec KSG semi-auto, or one of these in an autoloader. Why are they always pumps?

  • Lance

    Looked fun but never pass a Obama ATF test thed make it same as a Street Sweeper.

  • Zius Patagus

    I would guess that after buying Monolith Arms, Magpul couldn’t or didn’t want to make that shotgun work.

    • Cymond

      I never heard of Monolith until now. Some digging revealed that after buying Monolith Arms, Magpul discontinued their entire product line. Shame on them!

  • Vermin.308Winchester

    How could a spring that fit in that small a space move that much ammo disregarding the video evidence I don’t even see a spring? Look at this larger image and tell me what you think

  • Justin Galt (KRG)

    Brian, the designer/founder, is a very nice guy. He moved on from Magpul several years ago and has done some projects in the industry for other companies. Magpul wasn’t necessarily interested the shotgun per se, and it will never reach the functional prototype stage I’m fairly certain. I wouldn’t count on the P90 forend either.

  • Seamus Dubh

    If it was based on the P-90 Mag, why not make it look like a beefed up P-90.
    Kinda like How the AR-12 Shotgun is based on the AR-15 Rifle.
    I’m just saying.

    • Vermin.308Winchester

      Because they wanted to take as much as they could from the mossberg 500 bullpup conversion

  • Hieronymus Glossed

    The best part of the gun is definitely the p-90 magazine. Ergonomically this is the most compact and elegant solution for a 12 gauge hi cap magazine. Not sure how it measure up in practice but it sure looks sexy because the low profile of the mag doesn’t get in the way of a shooter’s traditional aiming stance like say, a wide drum magazine or long mags in the prone position.

    The frankenstein gun part of my brain wants to flip the reciever of an aa-12 upside down, reconfigure for bullpup and add the magazine.

    I’m sure there’s something mechanically that would get in the way of this concept… but still – hi cap, *compact* (relatively) 12 gauge, low recoil, select fire shotgun, mmm that’s some good shotgun.

  • Nathaniel

    There seems to be a lot of interest in hi capacity shotguns, but not of the kind that’s willing to shell out the cash to buy thousands of them.

    There’s really no job out there that a 10+ round magazine fed shotgun is better at doing than either a pump or an AR-15. It’s not surprising to me that it flopped.

  • Graham 1

    I remember seeing this trailer awhile back. I wondered what happened to it ever since. This sure clears some things up

  • Matt

    seems like overkill…

  • Edward

    The issue I can see with it would be the Shock from the gun firing would knock the rounds out of alignment after the first 5 or 6 shots just like the old P90 mags. however unlike the p90 they would require a MUCH stronger spring

  • BriZZell

    thats it, thats all you got for us on this #$^Y

  • Kid

    You spelled didn’t wrong.

  • James
  • Denver Garkie

    they need to make a 50 caliber semi rimmed 3&1/2″ with compatible case dimensions to the 500 S&W, then they cant be banned because they are technically DDs like all other shotgun shells even the 28 gauge is still subject to random bans by the BATFE by simply saying they dont have a sporting use. then we can make a semi auto(piston driven)+pump rifle/shotgun(with a rifle’d and smooth bore barrel that works with the 50 caliber shotgun shells 500 S&W magnum, and 500 S&W maximum, same dimensions as the 3&1/2 inch shot shell, in a design somewhat like the P12 imagine 25 rounds of 500 S&W magnum, maximum or 50cal double brass with triple ought buck, and to asociate the 500 shotgun shell with shotguns it will be called the 510 actual projectile diameter being .5 or less

  • Robert Kalani Foxworthy

    you could just make a 12 ga shell with a rebated rim to 20 ga in fact remington had over run of 20 ga that they convert to be 12 ga or was it the other way around..