mcb
Member
How about some redneck third part testing. Far from conclusive but interesting and topical.
t’s called innovation. Sometimes it works out, and sometimes it doesn’t. Check back in 20 years for the outcome of how he plastic case experiment worked out.
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.
True Velocity’s composite cartridges are not only lighter, but the composite acts like an insulator against heat, a factor that accelerates wear on any host firearm. The case reduced the chamber’s heat of a short-barreled Mk18 in a 90-round test by 26 percent with 28 percent lower bolt temperature and a 12 percent drop in the gas port’s temperature when compared to shooting brass ammunition. Those numbers are a result of one round a second over 90 rounds. To be sure that I don’t under emphasize the heat reduction advantage using True Velocity composite cases, when you shoot only a single round, the percentage of reduction in heat transfer is even more significant and pronounced.
As you pointed out, Specific Heat by itself doesn’t tell the whole story:It's not going with the case, the amount of heat it takes with it is pretty small. Do the math**.
<rambling warning>
If the propellent gasses heat a 308 Win brass case (~11 grams of brass, specific heat .38 J/g-K) from room temperature to 205 C (401 F) that would ~750 J of energy. The temperature is generously high most ejected 308 cases are probably cooler than that.
We know 308 pushes a bullet to roughly 3600 Joules of muzzle energy. Some of the initial chemical energy also goes into the kinetic energy of the propellent gases (roughly 2500 J in 308)
We also know only about 20-25% of the chemical energy gets converted to kinetic energy of the bullet. So we have roughly 16,000 J of chemical energy (assuming 22.5% efficiency) in the propellent before we pulled the trigger.
The overwhelming majority of the rest of that chemical energy goes into heat; heating the case, the gasses, the barrel etc. So the bullet takes 3600 J of the initial chemical energy as kinetic energy, the propellent mass takes 2500 J as kinetic energy leaving nearly 10,000 J of energy that most of is wasted a heat energy and the case takes only 750 J, slightly less than 8% of the waste heat goes with the case.
Polymers typically have higher specific heats than brass but specific heat is based on mass not volume. Making the assumption that they are using a form of High Density Polyethylene (Specific heat; Brass: 0.38 J/g-K, HDPE 1.9 J/g-K) then we can still expect the hypothetical HDPE case to take roughly 50% of the heat with it that brass does (assuming the same final temp). It likely takes significantly less as the cases come out very cool in the testing have seen.
The problem is that brass has a thermal conductivity that is 200-500 times higher than most polymers so while it takes less than 8% of the waste energy with it when it ejects it does nothing to slow how much heat passes through the case into the chamber that is a considerable amount of surface area compared to the bore and is also the place where pressures and temperatures are the highest at peak pressure.
** Doing everything in SI units cause thermal calculations in US customary units are a pain in the butt with keeping track of units.
<rambling done>
The biggest proof is simply the testing done with polymer ammo. They have shown that for a given number of rounds fired barrel temperatures are lower using polymer cased due to the insulation the polymer case provides over the surface area of the chamber. One example documented below.
https://www.gunsandammo.com/editorial/true-velocitys-new-polymer-cased-ammunition/247607
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.
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.
Not if the cases aren’t reloadable!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.
Not if the cases aren’t reloadable!
So reloaders go by way of the dodo bird?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.
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.What about Sig Sauer’s new Hybrid Ammunition?
A brass-steel hybrid.
View attachment 1032721
They’re completing for the same Army contract as the plastic stuff is.
It's a joke I need to stop using, I guess. Nobody ever seems to think it's as funny as I do.
For the guy that is not a reloader then if it is competitive in price with steel or aluminum then sure...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.
So reloaders go by way of the dodo bird?
For the guy that is not a reloader then if it is competitive in price with steel or aluminum then sure...
At over 60 a box for 308 currently, that's a long way to go.…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.
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 …”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.
So reloaders go by way of the dodo bird?
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.What about Sig Sauer’s new Hybrid Ammunition?
A brass-steel hybrid.
They’re completing for the same Army contract as the plastic stuff is.
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.At over 60 a box for 308 currently, that's a long way to go.