PCP Polymer Cased Rifle Ammunition

plastic_50-tm-tfb2

Last week I blogged about the Extreme Polymer Research’s polymer handgun cartridges. A US company called PCP Ammunition is trying to make mostly polymer rifle cartridges. Unlike Extreme Polymer Research’s handgun cartridges, these have a steel or brass base.

PCP Polymer Cased .50 BMG Round

The company had some cartridges on display at SHOW Show earlier this year. According to their website they will be offering polymer cased 5.56mm NATO, 6.8mm SPC, 7.62mm NATO, .338 Lapua Magnum and .50 BMG. They will sell direct to the public but their online store still has a “coming soon” sign posted on it.

There has been many attempts at polymer cased rifle cartridges. The primary problem with them is heat dissipation. Brass or steel cartridges absorb heat from the chamber before being flung out of the gun, keeping the chamber cool. Plastic on the other hand is a poor conductor of heat and will melt at a much lower temperature than metal such as brass and steel. Past attempts at polymer cased rifle ammunition has had users complaining of melted polymer residue gumming up the chamber and causing extraction problems.

[ Many thanks to George for the photo & Julio for the info ]




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.


Advertisement

  • Tommy

    “The primary problem with them is heat dissipation. Brass or steel cartridges absorb heat from the chamber before being flung out of the gun, keeping the chamber cool. Plastic on the other hand is a poor conductor of heat and will melt at a much lower temperature than metal such as brass and steel. Past attempts at polymer cased rifle ammunition has had users complaining of melted polymer residue gumming up the chamber and causing extraction problems.”

    This is wrong, and an often repeated misconception that stems from caseless ammo, where the ammo had issues with cooking off. People mistakenly thought it was because the brass somehow “carries” the heat away from the chamber. The problem was actually due to the fact that it did not have brass INSULATING the chamber from the heat source (burning powder). With no brass, the caseless ammo heated the chamber directly, causing it to get hotter. With direct contact with a fresh reloaded round, they would cook off.

    With polymer, it will keep the chamber COOLER, not hotter, because it insulates the chamber from the heat source (burning powder).

  • Joseph

    So, could a gun be designed with a chamber that better dissipates heat to fix that problem.

  • Bob Z Moose

    We’ve seen this before, haven’t we? Predicting failure in 3, 2, 1…

  • Basher

    A few years back, I ran a few boxes of the PCA (polymer cased ammunition) brand stuff through my AR. Functioned fine, I thought, but I never did shoot enough to really heat the chamber up. If they can get it to work it’s a great idea, as it’ll cut weight even further for our soldiers, but we’ll have to wait and see how this new crop of them works out. That they’ve made some in .50BMG is impressive, though!

  • http://suburbansdomain.blogspot.com/ Suburban

    Ya know, I kinda wonder how they control the headspace length on polymer and polymer/metal cases. Brass and steel can be adjusted, but polymer can’t, and I believe that the length/size of thin-wall plastic parts can be difficult to maintain with precision.

    I also wonder how costs work out for cranking out brass casings vs. producing metal case heads and polymer bodies, and then assembling them. I know brass is expensive now, but the assembly part would seem to be the spoiler.

    I have experience with manual and automatic assembly, injection molding, and insert molding. It’s sort of an interesting project they’ve got there. I’m not sure that I’d want to be involved with it personally, as an engineer, investor, quality tech, or salesman, but it’s interesting.

  • 18D

    This company seems to have a cool product, but I’m skeptical about whether or not they are having some problems. They introduced this ammo at Shot Show 2011 and said it would be available early this year. It’s almost 2012 and there has been no sign of the PCA. Their website always says coming soon. They might be having problems.

    On the other hand, the military has “cracked the code” on polymer cases with the MK323 MOD 0. I wrote a story for kitup a couple weeks ago about it. It’s a .50 BMG with a clear polymer case that’s being used in the M2HB. It’s been working for the last year of so without problems.

  • Robert

    There have been

  • Robert

    “Brass or steel cartridges absorb heat from the chamber before being flung out of the gun, keeping the chamber cool. ”

    Logic says the cartridge is hot because the gunpowder formally inside the cartridge just ignited, not because it absorbed heat from the chamber.

    Couldn’t it also be argued that a plastic cartridge would reduce heat transfer TO the chamber, thus lowering chamber temps?

  • Ramsey

    Copper has taken a 25% bath over the last couple weeks, and rumors are that it is going to head even lower as the economy weakens.

    I have no faith that the cost of ammo will decrease in response, as much of the price is due to high demand due to the economy weakening and belief that the government is going to go on a gun grabbing spree.

    Personally, I am long black powder, lead, and percussion caps. In a pinch I can whip out black powder myself, but lead mining and percussion caps are harder to do by oneself.

  • MarkM

    Polymer has been out for a long time. This generation of composites is different because more heat resistant compounds are readily available. Take a look under the hood of the family car – sensors, valve covers, even the intake manifold is composite.

    Issues with headspacing aren’t that high a priority – you don’t reload composites, and they can easily be made the right length the first time. As for the product cycle time from SHOT to actual delivery, let’s not forget the track record of another polymer maker, who regularly announces new products 366 days before delivery. If a reknown company with high profile interest consistently gets a pass on early product intros, I would expect one dealing with high start up complexities in a dynamic product line to take their time and get it right. They know the public won’t tolerate beta testing ammo – even tho those same buyers will beta test an Iphone case they waited one year to get, and which is already “improved.”

    We’ve been shooting plastic cased ammo for over 50 years – in SHOTGUNS. You have to wonder why the makers haven’t moved on long before now. It’s not rocket science.

  • SpudGun

    @ Tommy –

    ‘People mistakenly thought it was because the brass somehow “carries” the heat away from the chamber.’ – Um, I hate to correct you, but brass does indeed ‘carry’ heat away from the chamber. How do I know this? Because I’ve been hit with hot brass on more then one occassion. ;)

    As for the polymer cases, I’m surprised that more companies aren’t looking at this – http://en.wikipedia.org/wiki/Nanocomposite

  • netpc56

    once there was flachette-caseless ammos in research?I also wonder what .50 cal case weights?..http://www.freepatentsonline.com/4015527.html

  • Steve

    They’ll fail just like every company in the past trying this failed. You just can’t avoid laws of physics.

  • http://uncruel.com/ UnCruel

    I used some polymer cased 5.56x45mm ammo made by PCP several years ago. I didn’t have any trouble with it, but then again I’m not in the habit of overheating my barrel.

  • DaGryphon

    @Suburban;

    While I am an engineer, and I have some experience with polymers, it’s not my field. However, as an educated guess I would suggest the metal bases are probably molded or inserted while the polymer is hot. In any case I suspect the process is automated and after the up-front costs for the machines it’s probably a negligible per unit expense.

    As for the headspace length, I agree completely with your issues on holding the profile of a thin wall polymer while forming. However, as a polymer, it would be fairly easy to have an automated cutoff saw cleaning up that edge after forming, and that could be done with fairly respectable accuracy and at very high speeds.

    Personally, given the advances in polymer technologies over the years, I think this is an idea whose time has come, and I’ll be eager to buy some and test them when they become available to civilians.

  • http://ar15.com TrojanMan

    A few points on thermodynamics.
    1) Most of the heat generation from firing a rifle round is from friction of the bullet inside the barrel. Acceleration is greatest in the throat and friction peaks just in front of the chamber as the rifling makes its initial cut into the projectile.
    2) The gas concentration, generally described as a function of pressure (i.e. 35,000 psi for a SAAMI-max 9mm), is also greatest at this time. Gas temperature (PV/nR=T) also peaks as well. Convective heat transfer (as a function of either n/V or P -gas concentration-, T and surface area and cv) is thus greatest per unit of area.
    3) As the bullet travels down the barrel, if we can assume adiabatic expansion (which we can’t, since there’s a chemical reaction, but for simplicity’s sake…), both temperature and pressure will drop as volume increases per PV/T=C. Thus, as n/V and T decrease, so will the heat transfer rate (Qdot-c). What that means is that most of the heat transfer from the gas itself is going to happen in the barrel, close to the chamber, and that most of the energy not expended in pushing the bullet (and replacing any lost to friction) will exit the barrel in the gas, to be expended as flash and report.
    4) The only thing a polymer casing does for “insulation” is change the cv behind where the majority of heat transfer occurs. The throat and first few inches of rifling are still absorbing all of the energy they normally do – perhaps even a bit more because the chamber and casing are less available as sinks.
    5) All of that energy transferred to the throat and barrel is transported to the chamber, bolt, and other components via conduction. However, it takes some time to get there. That differential heating (resulting in differential expansion) is what creates “second shot shift” in precision rifles, for example.

    For low round counts, polymer should not appreciably affect the accuracy or reliability of a weapon. For open-bolt weapons like machine guns, it similarly will have little effect, as the time it spends in the chamber should not be enough to melt the casing. The problem comes in using it in closed-bolt automatic rifles.

    • OG_Locc

      I realize this post is two years old, but I just stumbled across it. So in the interest of helping anybody else who might stumble across it just like I did:

      What you’ve just said is one of the most insanely idiotic things I have
      ever heard. At no point in your rambling, incoherent response were you
      even close to anything that could be considered a rational thought.
      Everyone in this room is now dumber for having listened to it.

  • Big Jay

    I hope this idea works out. I have a feeling this ammo will be a lot cheaper than conventional ammo (given same type of bullet) due to the rising cost of copper. This should help stretch the military’s budget. Also, polymer is less dense and this should be lighter, and therefore easer for soldiers to carry. If they can create a polymer link for the M249 and M240 they might be able to shed 5 to 10 lbs off the weight of a fully loaded belt-fed machinegun. This will also increase the amount of ammo that can be carried in helicopters (limited by takeoff weight) and light vehicles.

    As to the polymer construction. There are a number of high temerature stable polymers on the market. Kevlar, nomex, and PBI are all used as firefighter turnout gear becuse of their flame/heat resistance. There are also silicone polymers used as baking equipment that can handle temps over 550 degF. A rifle such as a M4 will fail to function when it gets that hot. So I have the feeling a the gun will fail before the polymer ammo begins to melt. The cases sticking in hot chambers is an issue for varnish or lacquer coated ammo.

    Lastly, the isses of heat conduction in the chamber with brass and polymer ammo. Copper has a low heat capacity. The amount of cooling the chamber gets by heating up a small volume of copper is negligible.

  • David

    Coming soon: paper cartridges make a comeback.

  • Lance

    Like I said earlier plastic ammo with or with out brass bottoms doesn’t work. Ive 5.56mm plastic ammo and they either broke apart or melted in chambers and only seen them work well in ARs AK wouldn’t even feed them.

  • John Doe

    Well, I want a reliability test. Load them in a belt, and continuously fire them off until there’s a failure. If the MRBF is similar to that of the same gun firing brass rounds, I’ll be impressed. Lugging around ammunition in the desert is a pain, and this would be a big improvement.

  • Martin (M)

    While the technology is finally getting to a functional level, I still don’t see this stuff on the front lines. It may be great for the range or back areas, but I’m skeptical about how it will perform in a firefight. While the chamber may be somewhat insulated by the polymer, it will still conduct heat from the barrel. In sustained firing conditions, this means the tips of the cases will begin to soften and melt, and that won’t be good.

  • Tommy

    Spudgun, you’re not correcting anyone because you are wrong. The reason that brass is hot is because it absorbed the heat from the burning powder. Fire 1 round from a cold barrel, it will burn you just the same. It’s not rocket science, although I am an actual rocket scientist;)

  • 18D

    WTH Guys! Did none of you read my post! Everyone is speculating on whether or not polymer cases can work. Lance even said polymer cases don’t work. MK 323 MOD 0 ALREADY TYPE CLASSIFIED BY CRANE. The MK 323 is a polymer cased .50 BMG. It’s been used for the last year in the M2HB machine gun!

    Come on people! Brass case heads on polymer cases in high pressure cartridges with bottlenecks works just fine! Works just fine in the Ma Deuce at that! Now we just have to wait and see if this new commercial version is as good. STOP SPECULATING!

  • Sid

    Yes, we want it to be a reliable product before it is introduced. Yes, there have been failures before. But that does not mean the idea is not viable.

    Thankfully, the Wright brothers did not walk away after stalling on the first attempt and then going a whole 120ft on the second attempt.

    Point being that the thecnology may work out. Saying no before it is really tested and tried is backwards.

  • http://www.quarry.nildram.co.uk/ Tony Williams

    TrojanMan summed up the technical issues very well.

    Previous attempts at this (and they have stretched back over decades) have failed because of the melting problem, and also the tendency to shred in the fluted chambers of retarded blowback guns like the HK G3.

    However, technology moves on and heat-resistant polymers are much better than they used to be.

    If rounds are left in a hot chamber long enough for modern polymer to melt, I suspect that brass-cased ammo would have cooked off by then – something you want to avoid anyway, by clearing the chamber of any gun which has been firing heavily.

    Brass cases do extract some heat from the gun, but it’s only a small percentage of the total heat generated.

  • Lance

    Ive seen this whole debate 6 years ago when Maytag and others made polymer 5.56mm ammo they broke apart when firing too easily not a good combo.

  • SpudGun

    @Tommy

    I appreciate that you are a rocket scientist and that my evidence is analogous in comparison. ;)

    As brass can conduct heat more efficiently then steel or polymer and that this heat is then stored within it’s structure before being ejected from the weapon should indicate it’s heat removal properties.

    But hey, I’ve been wrong about stuff in the past, so why change a habit of a lifetime?

  • Rob

    But… why?

  • Andy

    I’d be more worries about polymer shavings being left in the chamber due to sharp feed ramps and the bolt hitting the next round on the way back. I have a couple of rifles that leave some scratches down the length of cases. I’d be curious to see what they do to plastic.

  • RCG

    The last ones I tried a few years ago didn’t do well at all.

    My rifle pulled the heads off and left the rest of the case in the chamber.

    I sure won’t be in a hurry to try any new ones.

  • El Duderino

    M2HB fires from a closed bolt, guys. If they can make polymer cases work with it I’m sure the jump to closed bolt rifles won’t be a stretch. M2HB barrels can get amazingly hot too, as anyone who’s done a barrel change and dropped it somewhere it wasn’t supposed to go (mud puddle, on top of plastic sandbags, etc).