The_Antibubba
Member
Antis will hate it
Can you imagine the Maryland DOJ trying to match a polymer casing to a particular gun?
Can you imagine the Maryland DOJ trying to match a polymer casing to a particular gun?
XM8: Polymer Cartridge Casings
- Thread starter starfuryzeta
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Hmmmm, getting rid of reloading......
Seems to me like the perfect way to help constrict the publics capacity to be armed up to parity. Once there is no more reloadable ammo, all one would have to do is cut off the supply of surplus and commercial ammo. Bingo! Dissarmed populace.
Seems to me like the perfect way to help constrict the publics capacity to be armed up to parity. Once there is no more reloadable ammo, all one would have to do is cut off the supply of surplus and commercial ammo. Bingo! Dissarmed populace.
griz
Member
I bought some of the PCA ammo at the last gun show. The price was about he same as white box. The weight difference is very noticeable. I can see why a soldier carrying 200 rounds, or a helicopter carrying thousands, would prefer the plastic. I'll weigh some tonight and post the results tomorrow.
Badger Arms
Member
So, somebody tell me why plastic (which is more elastic than brass) would be less reloadable? High-temperature plastics can easily withstand the temperatures we are talking. Seating the bullet should be a breeze and there doesn't need to be ANY resizing. Just decap, prime, charge, and seat with your hands!
Black Snowman
Member
Well, after the heating and firing depending on the formulation of the plastic I don't see it being able to retain the tension nessisary to prevent bullet set-back or maybe even hold the round depending on how loose the chamber was. Now if the plastic were intended to be reloadable maybe it would "remember" it's origional dimentions and go back to shape, which would make reloading a snap. I'm not sure if this is possible and affordable with current material technology. Any chemical/mechanical/material/plastics engineers here have some clues?
Poodleshooter
Member
They can already do that. Cut off the supply of commercial smokeless propellant or primers, and we're all back to scrounging our own mercury fulminate caps, and maybe making cordite at best.
I don't think my AR15 will run too long on FFFg Goex
They're already limiting reloaders in most states. My home state for example is passing more restrictive fire codes this year, limiting my possession of powder and primers even more. Those new restrictions are barely appearing on the radar of even the most attentive gun rights organizations.
Reloading has a very small political support base.
Regarding this polymer ammo, has anyone shot any? Any empty cases available for study? I'd be interested if it gets flame damaged and splits at the neck after repeated firings. I'd imagine case life to be somewhat reduced, provided that it is even reloadable.
Anyway, I have enough brass cases to last until I have great grandchildren.
FWIW, there's a thread in the ammunition forum on AR15.com about this ammo: http://ar15.com/forums/topic.html?b=3&f=16&t=179377.
MrAcheson
Member
Hi mechanical/composites engineer here. Your initial analysis seems pretty good to me. I would expect the pressure of the round to make the case deform. I would expect the heat of the burn to cause some stress relief so that it doesn't come back to quite the same shape afterwards. Its quite possible the inner layer of the plastic would be partially effected by the combustion as well which may degrade its properties in one way or another.
You might be able to recycle the polymer and remanufacture the composite case using the same brass case head, but reloading like brass might be a little much to ask.
I could be wrong though since I am not involved with this project in any way, shape, or form.
Brass Prevents Overheating
I seem to remember that when HK was developing caseless ammo for the G11, they found out they underestimated the role of the brass case in "absorbing" and "removing" heat from the action when it was ejected.
I'd want to be sure that plastic cases don't contribute to overheating and cook-offs.
John
P.S. Check out www.natec-us.com.
I seem to remember that when HK was developing caseless ammo for the G11, they found out they underestimated the role of the brass case in "absorbing" and "removing" heat from the action when it was ejected.
I'd want to be sure that plastic cases don't contribute to overheating and cook-offs.
John
P.S. Check out www.natec-us.com.
Vern Humphrey
Member
I once had an ejected case from an old Remington Browning .22 fall into my boot top. Even though I was wearing socks, it left quite a blister.
Cases take a LOT of the heat with them when they are ejected. I would think semi-automatic or full-automatic military weapons would not function well under combat conditions with "plastic" cases.
Cases take a LOT of the heat with them when they are ejected. I would think semi-automatic or full-automatic military weapons would not function well under combat conditions with "plastic" cases.
Badger Arms
Member
Vern, JWH:
You might be missing something here. Brass is a VERY good conductor of heat. That means it HEATS UP quickly and transfers that heat to the chamber if and only if the fired case remains in the chamber. Polymers are very poor conductors of heat and that heat tends to stay in the case and bore therefore I'd imagine that less heat will be transfered to the chamber than a brass case.
Of course, the flip-side is that a chambered round will absorb some heat from the chamber and take it away. I'm not entirely sure that the amount of heat it absorbs is significant. Perhaps plastic cases will be less likely to cook-off because of their insulative properties.
You might be missing something here. Brass is a VERY good conductor of heat. That means it HEATS UP quickly and transfers that heat to the chamber if and only if the fired case remains in the chamber. Polymers are very poor conductors of heat and that heat tends to stay in the case and bore therefore I'd imagine that less heat will be transfered to the chamber than a brass case.
Of course, the flip-side is that a chambered round will absorb some heat from the chamber and take it away. I'm not entirely sure that the amount of heat it absorbs is significant. Perhaps plastic cases will be less likely to cook-off because of their insulative properties.
Vern Humphrey
Member
That's our point, Badger.
When a brass case is ejected, it takes a lot of heat OUT of the gun, which means the gun runs cooler. A gun with plastic cases would heat up much faster than one with brass cases.
After all, the amount of heat (given identical powder charges) is the same with both cases. The plastic case cannot serve as a removeable heat sink.
In addition, in a closed breech system, an overly-hot gun and a chambered plastic cartridge could spell real trouble.
When a brass case is ejected, it takes a lot of heat OUT of the gun, which means the gun runs cooler. A gun with plastic cases would heat up much faster than one with brass cases.
After all, the amount of heat (given identical powder charges) is the same with both cases. The plastic case cannot serve as a removeable heat sink.
In addition, in a closed breech system, an overly-hot gun and a chambered plastic cartridge could spell real trouble.
Natec's website says their ammo is "currently under assessment by the U.S. Army," so hopefully they'll get some solid science on how polymer cases deal with heat management.
I don't know the physics of brass vs. polymer in this issue, so it's conjecture on whether polymer insulates the action from heating up in the first place, or whether it exacerbates it by not removing some heat like brass.
We'll still have plenty of heat in the barrel from the burning gas and bullet friction. I read about glowing, red-hot machine-gun barrels defending against human wave attacks in the Korean War. At what temperature will a brass case "stick" in the action due to a very hot barrel vs. this new polymer? And at what temperature will it just cook off? We need the input of some experienced combat machine-gunners who also have Ph.D.'s in physics!
I'm all for technological advances that, all things considered, truly represent a benefit to the user. These new cartridges could even have some surprise benefits once they're really well wrung out, but we'll see. . . .
John
P.S. Some guys over at AR15.com have been playing with this stuff since January of this year. See http://ar15.com/forums/topic.html?b=3&f=16&t=179377&page=1. They've had two dramatic failures, but, overall, mostly positive results.
I don't know the physics of brass vs. polymer in this issue, so it's conjecture on whether polymer insulates the action from heating up in the first place, or whether it exacerbates it by not removing some heat like brass.
We'll still have plenty of heat in the barrel from the burning gas and bullet friction. I read about glowing, red-hot machine-gun barrels defending against human wave attacks in the Korean War. At what temperature will a brass case "stick" in the action due to a very hot barrel vs. this new polymer? And at what temperature will it just cook off? We need the input of some experienced combat machine-gunners who also have Ph.D.'s in physics!
I'm all for technological advances that, all things considered, truly represent a benefit to the user. These new cartridges could even have some surprise benefits once they're really well wrung out, but we'll see. . . .
John
P.S. Some guys over at AR15.com have been playing with this stuff since January of this year. See http://ar15.com/forums/topic.html?b=3&f=16&t=179377&page=1. They've had two dramatic failures, but, overall, mostly positive results.
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Vern Humphrey
Member
We do know that -- when you eject a hot brass case, you're removing a substantial amount of heat from the gun.
Now, how would a plastic case "contain" an amount of heat equal to a brass case? If the heat isn't in the case walls, where is it?
Now, how would a plastic case "contain" an amount of heat equal to a brass case? If the heat isn't in the case walls, where is it?
Third_Rail
Member
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- Jan 10, 2004
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In the barrel.... I think.
I don't like the idea of polymer cases, still, even after considering everything. Call me old-fashioned, but I like blued steel, walnut, and brass. And I'm only 17!
I don't like the idea of polymer cases, still, even after considering everything. Call me old-fashioned, but I like blued steel, walnut, and brass. And I'm only 17!
Badger Arms
Member
Vern:
Don't get me wrong, I'm not for or against plastic. I do believe that most of the chamber heat is caused by the brass in the first place. The heat transfer TO the chamber and FROM the chamber probably equals out. The brass also would absorb MOST of its heat from the combustion itself rather than from the chamber. That's my guess.
I think that plastic cases have merit even now as low-cost practice ammo. I remember qualifying with 22's, with plastic bulleted .223, and with M193 but never with M855. To be fair, the Qualification guns we shot were all slick-sided M16's with 1-in-12 twist barrels. The 22lr's and plastic bulleted guns were abismally unreliable and innacuracte respectively. I think a plastic cased low-velocity training round could be used in an unmodified gun with great accuracy at perhaps a much lower cost. My opinion. They could make the cases Blaze-Orange for easy cleanup and identification.
Don't get me wrong, I'm not for or against plastic. I do believe that most of the chamber heat is caused by the brass in the first place. The heat transfer TO the chamber and FROM the chamber probably equals out. The brass also would absorb MOST of its heat from the combustion itself rather than from the chamber. That's my guess.
I think that plastic cases have merit even now as low-cost practice ammo. I remember qualifying with 22's, with plastic bulleted .223, and with M193 but never with M855. To be fair, the Qualification guns we shot were all slick-sided M16's with 1-in-12 twist barrels. The 22lr's and plastic bulleted guns were abismally unreliable and innacuracte respectively. I think a plastic cased low-velocity training round could be used in an unmodified gun with great accuracy at perhaps a much lower cost. My opinion. They could make the cases Blaze-Orange for easy cleanup and identification.
Vern Humphrey
Member
Let's take this a step at a time.
1. The heat is caused by the burning powder.
2. For a given charge and type of powder, there is a given amount of heat (let's say X calories.) There cannot be more heat generated than that.
3. If anything is taken out of the barrel, the heat (call it Y calories) in that thing taken out is subtracted from the heat remaining in the barrel.
4. The barrel now has less heat, X-Y calories.
From this, it follows that the more heat carried by the ejected case, the less heat remaining in the barrel.
Now, a brass case will carry more heat than a plastic case, and therefore will leave less heat in the barrel -- significantly less.
It may be postulated that this heat isn't in the chamber, but the barrel is made of steel -- an excellent conductor -- and the tendency is for the heat to flow from hotter to cooler parts of the barrel (anyone who had grabbed a just-fired machine gun by the barrel can attest to that.)
1. The heat is caused by the burning powder.
2. For a given charge and type of powder, there is a given amount of heat (let's say X calories.) There cannot be more heat generated than that.
3. If anything is taken out of the barrel, the heat (call it Y calories) in that thing taken out is subtracted from the heat remaining in the barrel.
4. The barrel now has less heat, X-Y calories.
From this, it follows that the more heat carried by the ejected case, the less heat remaining in the barrel.
Now, a brass case will carry more heat than a plastic case, and therefore will leave less heat in the barrel -- significantly less.
It may be postulated that this heat isn't in the chamber, but the barrel is made of steel -- an excellent conductor -- and the tendency is for the heat to flow from hotter to cooler parts of the barrel (anyone who had grabbed a just-fired machine gun by the barrel can attest to that.)
Badger Arms
Member
Hmmmm, then I'm not entirely sure that the brass is pulling that much heat out of the chamber. Firing a 22lr in a cold barrel, the casing comes out VERY hot IIRC. One trick I did with a Ruger 22 was to fire the gun sideways and catch the ejected casings in the air. I could only stand to hold them for an instant and then I'd toss them at my friend next to me on the firing line! The first round was no cooler than any other round. That was low-pressure round in a cold barrel-chamber.
I'm of the opinion that the brass case simply does a good job of COOLING THE IGNITION TEMPERATURE by sucking heat from the combustion in the chamber. I'd say that this factor has more to do with the brass heating than the theory that the brass is somehow acting as a cooling agent.
And since it heats up that fast, I'm sure it would be transferring some of that heat to the chamber as well.
Taking the AR-15 as an example, I can't recall the receiver getting hot around the barrel in spite of the fact that it was in constant contact with the barrel. I think the chamber temperature is temporarily spiked but without the friction of the bullet to heat it up more, it really doesn't get that hot in common use.
Sure, full-auto fire is bound to cause the throat to heat up rapidly and that heat combined with what heat is transferred from the brass to the chamber is significant. The one factor that might work against the brass-heat-sink theory is if SAW's with their open-bolt operation were significantly different in the cooling realm than are automatic rifles like the M-16 which operate from the closed bolt. I'd think that a case dwelling in the chamber is much more likely to draw heat from the barrel if that's a significant factor in the first place.
Being the selfless person that I am, I will volunteer to test this theory. Could somebody please send me an M249, an M4 Carbine, and about 50,000 rounds of M855? I'll supply the thermometers!
I'm of the opinion that the brass case simply does a good job of COOLING THE IGNITION TEMPERATURE by sucking heat from the combustion in the chamber. I'd say that this factor has more to do with the brass heating than the theory that the brass is somehow acting as a cooling agent.
And since it heats up that fast, I'm sure it would be transferring some of that heat to the chamber as well.
Taking the AR-15 as an example, I can't recall the receiver getting hot around the barrel in spite of the fact that it was in constant contact with the barrel. I think the chamber temperature is temporarily spiked but without the friction of the bullet to heat it up more, it really doesn't get that hot in common use.
Sure, full-auto fire is bound to cause the throat to heat up rapidly and that heat combined with what heat is transferred from the brass to the chamber is significant. The one factor that might work against the brass-heat-sink theory is if SAW's with their open-bolt operation were significantly different in the cooling realm than are automatic rifles like the M-16 which operate from the closed bolt. I'd think that a case dwelling in the chamber is much more likely to draw heat from the barrel if that's a significant factor in the first place.
Being the selfless person that I am, I will volunteer to test this theory. Could somebody please send me an M249, an M4 Carbine, and about 50,000 rounds of M855? I'll supply the thermometers!
Vern Humphrey
Member
Quote:
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I'm of the opinion that the brass case simply does a good job of COOLING THE IGNITION TEMPERATURE by sucking heat from the combustion in the chamber.
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We're saying the same thing. Now, if it were a bolt action weapon, and you simply left the case in the chamber, there would be no beneficial effect.
But in an automatic or semi-automatic weapon, the case is ejected, WITH the heat that would migrate to the chamber wall.
Quote:
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The one factor that might work against the brass-heat-sink theory is if SAW's with their open-bolt operation were significantly different in the cooling realm than are automatic rifles like the M-16 which operate from the closed bolt. I'd think that a case dwelling in the chamber is much more likely to draw heat from the barrel if that's a significant factor in the first place.
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Automatic weapons typically fire from an open bolt because a FRESH cartridge resting in the chamber when firing ceases will heat up, and may "cook off."
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I'm of the opinion that the brass case simply does a good job of COOLING THE IGNITION TEMPERATURE by sucking heat from the combustion in the chamber.
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We're saying the same thing. Now, if it were a bolt action weapon, and you simply left the case in the chamber, there would be no beneficial effect.
But in an automatic or semi-automatic weapon, the case is ejected, WITH the heat that would migrate to the chamber wall.
Quote:
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The one factor that might work against the brass-heat-sink theory is if SAW's with their open-bolt operation were significantly different in the cooling realm than are automatic rifles like the M-16 which operate from the closed bolt. I'd think that a case dwelling in the chamber is much more likely to draw heat from the barrel if that's a significant factor in the first place.
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Automatic weapons typically fire from an open bolt because a FRESH cartridge resting in the chamber when firing ceases will heat up, and may "cook off."
griz
Member
For what it's worth on weight, the plastic stuff weighs about 136 grains per cartridge while conventional rounds run around 170. Not as big a difference as I thought, but for 200 rounds that means less than 4 pounds versus 5 pounds for brass.
artherd
member
Kids- you're missing a critical point here.
OK, let's start off with a brass cartridge, with arbitrary numbers.
100 grains of powder driving a 250gr .338LM (bit hot for a .223 at 3,000fps.
80 watts of heat go into the barrel and muzzle blast, and 15 go into the just ejected case, and 5 go into the chamber indirectly through the case
Now a polymer cartridge.
82 grains of powder driving a 250gr .338LM at 3,000fps.
80 watts of heat go into the barrel and muzzle blast, and 2 go into the just ejected case. The case is such a good insulator, that effectively no energy goes into the chamber.
Can you guys see the benefit of this now?
OK, let's start off with a brass cartridge, with arbitrary numbers.
100 grains of powder driving a 250gr .338LM (bit hot for a .223
at 3,000fps.80 watts of heat go into the barrel and muzzle blast, and 15 go into the just ejected case, and 5 go into the chamber indirectly through the case
Now a polymer cartridge.
82 grains of powder driving a 250gr .338LM at 3,000fps.
80 watts of heat go into the barrel and muzzle blast, and 2 go into the just ejected case. The case is such a good insulator, that effectively no energy goes into the chamber.
Can you guys see the benefit of this now?
ShaiVong
Member
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I'm of the opinion that the brass case simply does a good job of COOLING THE IGNITION TEMPERATURE by sucking heat from the combustion in the chamber. I'd say that this factor has more to do with the brass heating than the theory that the brass is somehow acting as a cooling agent.
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But if you heat brass up to 120F, and a polymer case up to 120F, the polymer would have absorbed more energy, because it takes more energy to increase it 1 degree.
I think you have it backwards Vern.. Metals have a very low specific heat, which makes them good conductors, but that also means it requires very little energy to change their temperature.
The only limitation may be that the polymer case wouldnt stay in the chamber long enough to absorb energy as fast as brass would.. and thus brass may actually absorb more energy.
But considering the extreme heat caused by igniting a case, I would think more energy could be 'forced' into the polymer.
I'm of the opinion that the brass case simply does a good job of COOLING THE IGNITION TEMPERATURE by sucking heat from the combustion in the chamber. I'd say that this factor has more to do with the brass heating than the theory that the brass is somehow acting as a cooling agent.
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But if you heat brass up to 120F, and a polymer case up to 120F, the polymer would have absorbed more energy, because it takes more energy to increase it 1 degree.
I think you have it backwards Vern.. Metals have a very low specific heat, which makes them good conductors, but that also means it requires very little energy to change their temperature.
The only limitation may be that the polymer case wouldnt stay in the chamber long enough to absorb energy as fast as brass would.. and thus brass may actually absorb more energy.
But considering the extreme heat caused by igniting a case, I would think more energy could be 'forced' into the polymer.
Third_Rail
Member
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- Jan 10, 2004
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artherd, your math is faulty. If 80 watts are created, plus 15, plus 5, we have 100 watts from 100 grains of powder (your numbers, not mine). Now, in situation B, we only have 80 watts plus 2. 100 versus 82, to drive the same bullet of the same weight at the same velocity? I don't buy that.
As a counter example, let's say both have 100 grains of powder, but neither case is full. So let's see, in situation A the numbers are the same, but in situation B, 98 watts are now in the barrel. I don't like that at all, and I'd imagine the rifle isn't happy either.
So I guess what I'm saying is that most people don't like to take into account the great effect of the added thermal mass of the brass, but it's still there.
But then again, I'm no expert.
EDIT: SV, think about this: if polymer is such a great insulator, does it not insulate itself? Layer upon layer of whatever composition they're using (I suspect a spectra/nylon polymer), each layer a wonderful insulator even from itself. Now, wouldn't the heat from the gasses be transferred to the barrel faster than it could be transferred to the polymer?
As a counter example, let's say both have 100 grains of powder, but neither case is full. So let's see, in situation A the numbers are the same, but in situation B, 98 watts are now in the barrel. I don't like that at all, and I'd imagine the rifle isn't happy either.
So I guess what I'm saying is that most people don't like to take into account the great effect of the added thermal mass of the brass, but it's still there.
But then again, I'm no expert.
EDIT: SV, think about this: if polymer is such a great insulator, does it not insulate itself? Layer upon layer of whatever composition they're using (I suspect a spectra/nylon polymer), each layer a wonderful insulator even from itself. Now, wouldn't the heat from the gasses be transferred to the barrel faster than it could be transferred to the polymer?
Vern Humphrey
Member
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SV, think about this: if polymer is such a great insulator, does it not insulate itself?
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Exactly. Which is why the polymer case will NOT carry as much heat as the brass case when ejected.
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SV, think about this: if polymer is such a great insulator, does it not insulate itself?
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Exactly. Which is why the polymer case will NOT carry as much heat as the brass case when ejected.
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