Spiral Case Ammunition

pat_20100282112-tfb

A patent application has recently been published for a novel cartridge case design. The inventor proposes a three part case with a metal base, spiraled polymer center and brass or plastic head.

The inventor claims that the spiraled case will reduce friction when extracting. I guess, in theory, the case would revert to its previous shape after being flattened by pressure during firing. The flutes would help reduce friction during extraction and reduce heat being transferred from the chamber wall to the plastic.

What this design does not address is one of the major advantages of brass cases. Heat from the gun and from the burning propellent is transferred into brass cases which are then ejected. Plastic cases cannot transfer this heat. To counteract this, some sort of heat sink would need to be added to the weapon. The reason plastic cases are only commonly used for shotgun shells is that because military firearms firing full-auto generate a lot of heat, the heat eventually builds up to a level that causes the cases to melt. Plastic then sticks to the chamber and causes reliability problems.

UPDATE: A photo of this case from a presentation given at National Small Arms Conference ’09 by Colt Defense and BML Tool & Mfg. Corp.

Thanks to Mark for the link.

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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.


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  • Mark K.

    LIGHTWEIGHT AMMUNITION DESIGN – presentation

    http://www.dtic.mil/ndia/2009infantrysmallarms/tuesdaysessioniii8550.pdf

    • http://www.thefirearmblog.com Steve

      Mark, thanks for the link.

  • http://www.dminorartisan.com M.W.

    I’m intrigued , now let’s get this baby firing from a Piston AR

  • Matt

    Looks like an answer in search of a problem. It will only reduce case capacities and cartridge pressure capacities whilst not improving much on the excellent service were get allready from brass’ inherent lubricity.

    It’s hard to tell but that picture looks like a .50bmg. I could understand this design for large cartridges like that as long as it doesn’t reduce C.U.P restrictions. As it would save weight on lardge cartridges like that. And heat wouldn’t be as much of a problem on a bolt .50. And you would be able to carry more.

  • seeker_two

    Why not? Multi-part cases worked so well for Custer’s Army and the British at Islalawanda…..

  • Sam

    I’m not sure you’re right about the heating. In a firearm, the heat is generated inside the case by the burning powder. It’s then conducted into the case, and from there it’s conducted to the chamber wall. Because the plastic is a worse heat conductor than brass, more of the heat would stay in the case, and less would be transferred to the chamber walls.

  • John C

    I remember PMC used to offer plastic cased .223 ammo. I never had a problem with it, but it still didn’t seem like a good idea. I think it would be easy to break/ bend the plastic

  • Rootshot

    I had the opportunity of shooting some polymer cased 223 (I believe it was Natec) several years ago. Accuracy out of a sub-MOA varmint rifle was unimpressive. The surface had fine ridges to aid extraction and the base was brass. They seemed to work fine as sporting cartridges, but I would not bet my life on them.

    I would be much more interested in seeing a domestically manufactured steel case round with a non-polymer coating.

  • xstang

    If this ammo were dirt cheap, I’d buy it. Being plastic, it should cost less to manufacture than wolf IMO.

  • Bryan S

    @Sam – I think that some of that heat that would normally stay in the gun (barrel, bolt, chamber) is carried away by the brass, which, being greater in mass, stores heat better than plastic does, and thus, carrying away that heat when ejected.

    I would think that a lot of the heat in firearms comes from the barrel and conducts to the chamber, in low rates of fire, the brass does help in a marginal manner to carry heat away from and out of the gun.

  • Lance

    Sounds promising I think this may be a something for the army to looking into to reduce weight. It will have to be very heat resistant or they would melt into the chamber and action of the weapon making a permanent jam.

  • Cymond

    Sam, I suspect a lot of the heat comes blasting out of the case neck (hot gas). The throat of the barrel is probably very hot.

    I’m suspicious of the multi-part case (maybe with some super epoxy). I’m also uncertain about the fluting. I don’t understand advantages of this design but obviously some smart & wealthy people put a lot of time & money into developing it so somebody must think its a good idea. Promising new technologies at least merit trial & evaluation.

  • http://www.accurate-mag.com Anthony Battaglia

    My father and his ideas….to all this project is moving forward very fast, alot of questions still remain, but very cool technology, a lot more to follow

  • Emperor Fabulous

    The biggest problem I see with cartridge cases made of multiple parts is what happens when those parts come apart after firing (as things always eventually break where they can break). If the body of that plastic cartridge case separates from the head, it’ll make for a nasty jam when the next round is slammed home.

  • Jim

    Congratulations and much luck to the Battaglia family.

  • http://www.milgeek.co.uk Milgeek

    Can I ask about the heating problem…

    Would the fluting around the cartridge help in the disipation of heat generated inside the cartrdige during firing?

    If I understand the design correctly the fluting would actually reduce the area of the surface of the cartricge that would be in contact with the breech (?) – and so this might help in keeping the cumalative tempreture down (?)

    Just an uneducated guess.

    By the way, is this heating problem why caseless ammo hasn’t taken off?

  • subase

    Yeah my viewpoint is that of Milgeek and Sam, wouldn’t the polymer be just a much better insulator of the heat, keeping the chamber actually cooler, and just increase chamber pressure? (which would increase velocities)

    This would also greatly increase rate of fire by preventing rounds from firing due to the hot chamber. (cook off)

    Also the twist of the spiraling may mechanically aid extraction by pushing up on the chamber walls and directing some of combustion pressure through the polymer casings spirals horizontally, thus making the case ‘wiggle out’ out of the chamber. Which is quite ingenious.

    Sort of an inversion of the physics of the spiral nail.

  • Emperor Fabulous

    One problem that may arise from the spiral flutes is that when it’s pressurized from within, it might try to lengthen, to straighten out the spirals. If that lengthening is too great, it could create a jam.

  • subase

    I think their counting on it to lengthen or at least wiggle out with it’s spirals, probably a bit of both.

    This would aid extraction as it would provide partial extraction due to some of the rim sticking out.