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Why Plastic Cases Are a BAD Idea

Discussion in 'Handloading and Reloading' started by jski, Oct 19, 2021.

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  1. mcb

    mcb Member

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    How about some redneck third part testing. Far from conclusive but interesting and topical.

     
  2. bassjam

    bassjam Member

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    Not even sure why we're arguing over this unless some of you regularly run fully automatic belt-fed guns. It's going to be a non-issue for pretty much everything else. I'm not even sure it's an issue for auto weapons, I'm not convinced the ability of brass to remove heat is taken into consideration when designing those firearms.

    But those arguing that polymer will be worse aren't taking into account where the heat is coming from. The heat is generated INSIDE the case. For the heat to be transferred to the firearm, first the brass has to accept the heat before it can transfer it to the firearm. If a polymer case doesn't accept heat as readily, it also won't be able to conduct as much heat to the firearm. The real test is to see what the air temp is inside the case as it's ejected. I'd be willing to bet the polymer case will have a much higher internal air temperature.
     
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  3. jski

    jski Member

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    Keep in mind:

    Why is water such a great coolant in car engines? Because is has a VERY high specific heat. Substances with high specific heat are good for cooling things. And brass has a high specific heat compared to other metals.
     
    Last edited: Oct 19, 2021
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  4. mcb

    mcb Member

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    The biggest advantage I see is the resulting ammunition is ~35% lighter than the same cartridge in brass. That means a soldier can carry slightly more that 50% more ammo for the same weight. You can never have too much ammo, unless you are drowning or on fire.
     
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  5. jmr40

    jmr40 Member

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    This.

    Most experiments fail to accomplish their intended goals. Many only show very minute improvements. But at least we will know one way that won't work. That doesn't mean that you stop innovating. You build on those small improvements and keep tweaking the design and eventually we see a significant improvement.

    It's been said that Thomas Edison invented 3,000 light bulbs that didn't work before he figured it out. Not sure that number is accurate, but there were a lot.
     
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  6. mcb

    mcb Member

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    Most common polymers have a specific heat 2-4 times higher than brass and both are significantly smaller compare to water. Brass is 0.38 J/g-K , most polymers are between 0.88 and 1.6 J/g-K, water is 4.2 J/g-K Water also has the advantage of being a liquid which greatly reduce the thermal resistance at the interface between the water and what ever it is cooling. This makes up a lot for it relatively low thermal conductivity similar to many polymers.

    You can make all the arguments you want but that experimental results with True velocity I have been able to find all point to the fact that from a thermal point of view the polymer cases are performing better than brass. I have given two examples up thread and if I find more I will add them to the thread.

    ETA: Found another example of testing.

    https://www.gunsandammo.com/editorial/true-velocity-sierra-bullets-team-up-to-produce-ammo/372002

     
    Last edited: Oct 19, 2021
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  7. jski

    jski Member

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    As you pointed out, Specific Heat by itself doesn’t tell the whole story:

    Specific Heat Capacity of Metals Table Chart
    Metal J/(kg-K)
    Aluminum
    921.096
    Brass (Yellow) 401.9328
    Carbon Steel 502.416

    So aluminum has a higher spec. heat than either brass or steel but if you were using aluminum, the mass per case would be a fraction of that for brass or steel. Same for a polymer.

    But the heat ejected is much less than I would have expected. That’s the killer for my assumption. You can’t fight the numbers. I surrender! Long live plastic. (That’s like fingernails down the chalkboard!)
     
    Last edited: Oct 19, 2021
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  8. AJC1

    AJC1 Member

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    My real problem with this for our uses is three pronged. 1. Cost- this stuff is very expensive. 2. No reloadable case. 3. Trash left everywhere. The military probably doesn't care about any of those.
     
  9. jmorris

    jmorris Member

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    The biggest advantage I can see is a reduction in cost. Every new technology comes with a price tag but you can be certain the cost of the plastic is less than the cost of the brass.

    However, it must function with equal or greater reliability. The case I posted above was one I fired (out of a semiauto) when given about 1000 rounds of them from a friend that knew I had a .223 contender.
     
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  10. mcb

    mcb Member

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    I think cost will come down alot as volume goes up, especially if they actually get a military contract. The contract and high volume will help them pay off all the initial R&D costs and initial equipment investments and the price to produce should drop noticeably.

    I agree with the reloadability. But this case was not mean for that market. We never complain about reloadability when someone releases a new rimfire cartridge. It will be interesting to see, if the product is successful, if True Velocity or a third part develop a way to reload it. Everyone said you can't reload steel or aluminum cases too and we seen that done. It might happen for this polymer stuff too.

    Poly rifle cases won't be any better or worst than shotgun shells. Like shotgun shell with steel bases clean up with a magnet will be fairly easy. If it is truly non-reloadable then the spent cases have less value left on the battlefield than brass cases that can be recycled by low tech means easier than polymer/steel cases left on the battlefield.

    If the cost comes down it will be successful with the crowd that does not reload almost certainly.
     
  11. jski

    jski Member

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    Not if the cases aren’t reloadable!
     
  12. jmorris

    jmorris Member

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    That’s only a concern if you care about them being reloadable. CCI blazer aluminum cases wouldn’t have stuck around this long if being intended to use only once was a problem across the entire market.

    Believe it or not but reloaders are a small minority of firearms owners.
     
    Last edited: Oct 19, 2021
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  13. jski

    jski Member

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    So reloaders go by way of the dodo bird?
     
  14. Buzznrose

    Buzznrose Member

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    I read this whole thread and am amazed at the discussion! I definitely learned a lot and appreciate those who explained this so well!

    I think this ammo will be a huge win down the road. If the savings per round materialize and make sense, I see this being huge for guys who shoot military calibers like .223 and 9MM.

    I guess time will tell. Thanks again for the science class!
     
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  15. jski

    jski Member

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    What about Sig Sauer’s new Hybrid Ammunition?
    A brass-steel hybrid.
    upload_2021-10-19_16-47-43.png

    They’re completing for the same Army contract as the plastic stuff is.
     
  16. AJC1

    AJC1 Member

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    That's the very high pressure stuff vs the plastic? Not the same at all imo. More than one way to skin a cat I guess.
     
  17. Twocanary

    Twocanary Member

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    Thought it hilarious; something Groucho Marx would say. Continue doing so and you might could be a Marxi-cist. JK! Btw, I thought everybody reloaded so they could shoot more for the same amount of money.
     
    Last edited: Oct 19, 2021
  18. jmorris

    jmorris Member

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    I doubt it, aluminum, steel and plastic cases thus far have not stopped us. The plastic case itself isn’t a new invention. I remember my LGS had the USAC plastic 38 spl for sale back in the ‘80’s and it was reloadable.

    CCD6FDA8-A551-43A6-AD63-D5B45C23FFB7.jpeg
     
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  19. AJC1

    AJC1 Member

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    For the guy that is not a reloader then if it is competitive in price with steel or aluminum then sure...
     
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  20. Buzznrose

    Buzznrose Member

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    No, but the percentage of shooters who reload are dwindling IMO. I’d bet, from my experience with shooting buddies, range visits, and weekend competition, that no more than 15% of shooters reload their ammo. And those that do often pass on cheaper stuff like 9MM and .223 (pre COVID) and just load stuff that they feel is worth their while.

    For example, my primary shooting partner reloads all revolver cartridges and his hunting and long range rifle ammo, but usually buys .223, 9MM, and 7.62*39 range ammo. He reloads some .45 ACP but when it’s on sale, buys a case or two, and really doesn’t shoot it much.

    Personally, I am just getting back into reloading after many years of buying ammo. I plan on starting with .44, but time will tell what else I get into.
     
  21. jmorris

    jmorris Member

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    …and works…but yes, that would be the idea. If you sell your product for 10% less than the equivalent from the competition but have a 20% lower cost, you’re in a good place to be.
     
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  22. AJC1

    AJC1 Member

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    At over 60 a box for 308 currently, that's a long way to go.
     
  23. jski

    jski Member

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    I thought the figures showed just the opposite? The number of reloaders is increasing at a good pace. Call RCBS or Redding or Starline or Alliant or Hodgdon or … “Sorry due to high demand for our products our service people are very busy …”
     
  24. mcb

    mcb Member

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    No I would not think so. The success of True Velocity does not preclude tradition brass cases from being made. I think even if True Velocity become the prime supplier of small arms ammunition to the US military the other manufactures are going to continue to make brass cases for a long time to come. For the military application the polymer case has some advantages but that does not somehow make brass no longer what it is.
    Brings different advantages. The Sig case is stronger and they are running the pressures up to pressures brass cases would have a fair chance of failing at. The commercial version of their 6.8 cartridge the 277 Fury is SAAMI spec at MAP of 80,000 psi. This is 15,000 psi higher than any other SAAMI approved cartridge. That pressure is right at the bottom edge of the pressure where brass starts to flow (depending on hardness) and could cause cases head to extrude into extractors and ejectors features of the bolt head and might rupture if not fully supported.

    Don't forget Textron that is proposing a 6.8mm case telescoping polymer cartridge, that bring another set of benefits and liabilities to the party.

    Its going to be interesting to see what comes out of the NGSW program that started this latest round of development. I doubt we get a new service rifle and squad machinegun from it but we might.
     
  25. Buzznrose

    Buzznrose Member

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    Yeah, but they are probably trying to recoup some up front R&D and investment costs. All other components (Bullet/primer/powder) being equal, if the poly case costs half or less than a brass case, they should be able to get prices down in a short time. A large military contract would certainly speed things up on that end.
     
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