In the mid 60's, I had some 20 gauge all plastic shotshells, no metal at all other than primer and shot. Headstamp was "Wanda"Originally Posted by Borderland
In the mid 60's, I had some 20 gauge all plastic shotshells, no metal at all other than primer and shot. Headstamp was "Wanda"
I always enjoy experimental ammunition efforts, and always wish parties involved good luck and happy outcomes.
During my days of heavy shotgun ammunition expenditure, I eventually moved to Activ-only reloading- not for any real reasons beyond thinking it was neat, and I'd agree that it's an apples and oranges sort of comparison to consider Activ hulls against polymer cased rifle-caliber ammunition.
I'm not any sort of technical expert on alternative case technologies, but I think that we are all driving toward some common concerns and thoughts.
The heat absorbed by a brass case from the burning gunpowder in a single instance of firing will certainly get that case hot, but difference in thermal energy present in the gas if the cartridge case were an insulator instead of a brass conductor is absolutely minimal.
The open-bolt design of machine guns will limit the "time-in-hot-chamber" of the polymer cases. While I don't know the particular formulation & coatings used in the True Velocity (or any!) polymer-cased ammo, there will be a temperature/time envelope that the ammo will be able to safely operate inside of and the primary difference from a Failure Modes Effects & Analysis standpoint between a polymer case and a brass one would be that the brass would absorb heat and transfer it to the powder/primer and cause a cookoff, while the polymer would mechanically degrade. The use of open-bolt machine guns should really strongly mitigate this, and the polymer case failures I'm imagining would either be some case cracking/splitting during the firing process, or some fragments of polymer materials staying behind in the chamber after firing.
I don't really have any ideas of what that temperature/time operational envelope of True Velocity in particular, or polymer-cased ammo in general, might be. If someone had a big pile of 5.56 and an M16, I can imagine some experiments. For open-bolt aviation, armored/mounted, or infantry machine guns, the weight reduction seems very valuable and the likelihood of ammo failures seems low.
I'd buy some check out just because it seems neat, and I were doing Desert Brutality/2 Gun Action Challenge Match sort of shooting in some division where I had to wear armor and carry all of my ammo on me during the entire match, I could see the value for the commercial market. For general use however, the military seems like a far better fit, and far more likely to realize real value, than myself as a simple and filthy civilian.
While the weight benefits are neat, I actually find higher-pressure cartridge case design more interesting than even polymer case ammo. The brass-body, steel-head is neat. I was once told by someone who I thought was in a position to know, that the future would be in welded stainless-steel cartridge ammunition. That was over a decade ago, though, so who knows?
Per the PF Code of Conduct, I have a commercial interest in the StreakTM product as sold by Ammo, Inc.
I used to think this was a thing, because hot brass is hot and it makes sense. It's a heat v. temperature thing, where the hot brass is hot because of the thermal conductivity of brass but the actual heat load removed from the weapon is actually pretty low. Like if you light a match and put it under a cast iron bathtub, the match temperature is very high but you instinctively understand it's not going to heat the bath water, but if you take two cups of hot water and add a cup of cold water the heat will be lowered.
The brass does take away heat, but not enough to affect the function of most weapons for a long period at which point the barrel is a bigger issue. I think it got muddled because a lot of the initial interest was in caseless (G-11 and German Space Magic) and that seems to get confused with plastic cases. The limitations seem to be in material science and the ability of plastic cases to take abuse, like you mentioned. Debris, deformation, etc. In caseless ammo the complete lack of an insulator leads to cookoff problems.
This is actually a misconception that arose from trials with the HK G11 / Caseless ammunition.
The Caseless guns were overheating at a faster rate than brass cased guns, which lead to the belief that brass was removing heat from the weapon.
Later, it became clear that brass does not remove heat from the gun at all. Brass actually transfers quite a bit of heat into the weapon...just not neatly as much as caseless. IE
Caseless = 100% heat transfer, as its all the powder is burning in direct contact with the chamber and nothing is ejected.
Brass = (70?)% heat transfer. Powder ignites and heat up brass, which then heats the chamber, but to a lesser extent than caseless as powder is not in direct contact with chamber, and brass is ejected before 100% heat transfer can take place.
But brass is absolutely adding heat rather than extracting it. You can test this at the range, just take a cold unfired gun, fire it once, and pick up the brass - its very hot. And since the gun is cold, thats heat that was produced inside the brass, rather than extracted from the weapon.
Testing with polymer case ammunition has shown that polymer ammo = cooler weapons chambers. The reason is that polymer is a poor thermal conductor (hence why frying pan handles are polymer coated, or why why polymer AR hanguards heat up less rapidly than aluminum ones, or plastic coke bottles dont cool as quickly as aluminum coke cans, etc). So when smokeless powder burns in a polymer case, the polymer transfers less of that heat into the chamber. It's also why polymer cased ammo is cool to the touch after ejection.
More specific data can be found here:
https://www.gunsandammo.com/editoria...ynamics/331240
One of the concerns associated with the M134D is the way it can cook-off live rounds with brass-cased ammunition. A cook-off occurs when a cartridge sits in a hot chamber and spontaneously fires because the powder inside the case becomes hot enough to ignite.
Dillon has a 1,500-round test they run on the M134D and found brass-cased ammunition will cook-off after sitting in the chamber for anywhere from 3 to 60 seconds. Using True Velocity’s composite-cased ammunition, Dillon recorded a 20-percent lower bore temperature (thanks to the case insulating the chamber), which ultimately led them to a 2,200-round test on the ammunition. Dillon had to wait 5 minutes before one case got hot enough to melt — but the bullet never left the barrel. The absence of cook-offs in a Minigun should bring a welcome sigh of relief from end users.
Similar reduction in chamber/barrel temp has been found in testing of Textrons LSAT CT polymer cases, although I cant find the documents at the moment.
Heres a cool recent test of the TV .308 ammo showing its heat reduction vs brass using FLIR:
Posted to YouTube on Oct. 17, 2018, by Bigshooterist
Polymer Cased Ammo (PCA Spectrum) by NATEC was introduced in the mid 2000's and was offered primarily in 5.56x45 though other calibers were in the works. It featured a polymer case with a brass rim. It was tested in an article in Small Arms Review Magazine (link following) in 2006. If you would like more extensive testing of this new. old stock I have around, please let me know in the comments and I'll be happy to accommodate as many requests as I can. Firearm is a BCI Defense Pistol with SB Tactical collapsible Brace. Optic is Trijicon Reflex from Optics Planet. Suppressor is a Gemtech TREK-T Titanium 5.56 suppressor.
Here are a couple questions I have that I didn't see answers to or missed them.
What is the case wall thickness difference between brass and polymer? This doesn't seem to matter in some cartridges as there is plenty of interior volume to get equal velocities between the different cases. However if polymer cases were used in other cartridges there may be an issue with case volume for powder capacity and/or pressures.
Along similar lines is the 30% weight reduction case to case or cartridge to cartridge? It wasn't clear to me. The Shell shok steel body brass head cases are 50% lighter than brass and have more interior volume while being able to handle equal or higher pressures than brass. I'm sure it was looked into or considered. Maybe it isn't plausible for bottle neck cartridges?
I'm curious how the polymer cases hold up to side impacts to the case body and bullet set back from repeated loading/feeding? Again I'm sure it was considered but I think back to military and LEO days and how often double feeds or nightmare feeding issues with brass case ammo was to clear. Especially after someone rammed the bolt into a double feed repeatedly. If the crimp on the bullet is the same or better that's good but if it is less there is already bullet push back with repeated chamberings in some settings. Some of the set back bullets I saw from patrol rifles were quite scary.
Per some of TV's videos, they have described the ability to adjust the interior volume of the cartridge cases in order to optimize the burn rate for a given powder. They claim that this optimized burn rate + the better thermal efficiency of the polymer case allows them to match brass case velocities with 8-10% less powder.
No idea whether this is real or marketing, but their chrono numbers for their .308 cases have been comparable or better than brass in initial youtube testing.
https://www.youtube.com/watch?v=0GVT0F15T78
In terms of weight, someone on Reddit very kindly tore down one of their .308 TV cartridges to give us the specs:
https://www.reddit.com/r/guns/commen...ty_308_weight/
TV .308 168gr Cartridge: 293.9gr
TV .308 empty case w/ primer: 82.3gr (Large rifle primer ~5gr so 77.3gr for empty case)
TV .308 powder charge for 168gr .308 load: 42.5gr
168gr Hornady Amax .308 Brass control: 370.7gr
-->
TV .308 168gr loaded = 19.04g
TV .308 empty case = 5g
Compared to brass empty cases:
https://www.m14forum.com/threads/bra...cturer.163875/
"The Mean weight in grains of the listed manufacturers brass is as follows: Winchester at 157.13, Winchester nickel plated at 159.82, Hornady Match at 166.29, PPU at 166.94, Federal 308 WIN at 176.90, Lake City NM 68 at 177.55, Lake City Match 91 at 177.98, Lake City Match 77 at 178.45, GFL at 178.89, WCC at 179.48, PMC at 179.50 and CBC Nato 12 at 183.09."
--> Avg brass .308/7.62 brass case = 173.5gr / 11.24g
------> TV .308 Case @ 5g = 55.5% weight reduction vs Brass .308 case
Avg 147gr 7.62Cartridge = 173.5gr brass + 5gr primer + 147gr bullet + 42.83gr powder
= 368.33gr / 23.87g
TV 147gr = 82.3gr TV case + 147gr bullet + 42.83gr powder
= 272.13gr / 17.63g
--> TV 147gr = 26% weight savings over 7.62 M80 Brass
...
As you mentioned, Shell Shocks awesome 9mm cases offer a 50% case weight reduction, which is very close to the 55.5% of the TV polymer case (although without the nice weapon heat reduction.)
I was extremely excited ~4 years ago for SS to release their rifle cases...which seems to have been put on back burner due to technical difficulties with the design.
The initial rifle cases used the same Aluminum Base we see with their proven 9mm loads. Unfortunately something went wrong there when it was tried with rifle rounds, as the initial short release of .223 cases for NovX ammo were pulled off the market, and all of Shell Shocks subsequent Rifle case teasers now show a new design.
The new SS Rifle case uses the same thin wall nickel-stainless body, but now uses a heavily scalloped steel base. This would be lighter than brass, but a good bit heavier than the original Aluminum base. And so far these seem to be exclusively prototypes made for SHOT Show and Facebook/Instagram teasers, having been hinted at since 2019.
Agreed. One small nit - the M2 fires from the closed bolt and the headspace and timing needs to be set each time a barrel is mounted.
Okay - I was pretty sure, but going from memory and never have done more with one than fired a couple of rounds at a car on a fam fire day. I do recall that the headspace and timing were critical to set properly every time a barrel was mounted in that one, where the others are supposed to be fast change barrels.
Until these cases are 100% injection molded polymer that cost .05¢ to produce and are designed as a recycleable throw away, they won’t make sense for the civilian market. I see the benefit as a range focused cheap, acceptability reliable cost savings for range fodder.
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