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U.s. Army Next Generation Squad Automatic Rifle

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#141 Ivanhoe

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Posted 19 June 2017 - 0217 AM

That'll be the Mark 1A version.



#142 Chris Werb

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Posted 19 June 2017 - 0419 AM

Well, that could be "cool looks" photos.
 
This guy
IMG_5656-875x700.jpg
is obviously not aiming at anything that isn't high above his altitude.

 

img_5656-875x700modified.jpg

The red lines show the possible angle judging by the markers on the sight, might be exploited if the sight isn't above the barrel.

The green lines show the maximum possible angle (which is likely too large because the upper line was drawn assuming some optic likely too far up in the sight) to assuming that the sight is above the barrel, and sight line thus restricted by Pike's nose.

 

I don't know this type of sight (it looks like a sight for dumb 40 mm rounds), but it seems obvious to me that this guy shows an exaggerated elevation angle.

 

 

Alternative explanations:

 

1. This is indeed a looks cool pic, - the model did not realise he had to use the sight, but the photo does reflect the actual launch angle or thereabouts.

 

2. You don't actually need to use the sight as the weapon is powered and guided. There is a lot of tolerance in hold angle.



#143 TTK Ciar

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Posted 19 June 2017 - 1338 PM

In machine cannons at least there are aluminium cartridge cases in use. mostly in fighter guns. So scalig this down to handheld size is a possibility. I have never thought of titanium for this purpose. Isn't it too stiff (elasticity module) for the purpose of fitting tighter into the chamber on firing?


Scaling down existing large-caliber aluminum cartridges might be possible. It depends. Since stiffness is proportional to the cube of material thickness, a scaled-down aluminum part will exhibit disproportionately lower stiffness. If it is too flimsy to handle the mechanical stresses of loading, something has to change -- either use of an alloy with a higher flexural modulus (which is linearly proportional to stiffness) or increase case wall thickness (so no longer a proportional scaling down of the original), or both.

Shep854 says he's fired aluminum-cased munitions, so I guess they exist. I'm curious to learn what alloy they used for that, whether they have thicker case walls than their brass equivalents (and consequently reduced case volume?), and how much they cost. Maybe the solution is already here?

As for titanium, again it depends on the alloy. Some titanium alloys are quite malleable:

http://matweb.com/se...65498f93cba0959

http://matweb.com/se...bcc4216982c478c

The main trick is bringing down the price. Titanium oxide is very plentiful (Ti is 9th most abundant element in Earth's crust), but cannot be economically reduced. Commercial titanium is reduced chemically from titanium-bearing compounds with high reactivity. This and the controlled environment it requires for alloying make it expensive. A better catalyst than carbon might make titanium smelting feasible (smelting TiO2 with carbon makes TiC which is as hard to reduce as TiO2). There are a lot of people working on this right now. We'll see if anything comes of their labors.
 

Folks are trying to achieve this now with polymers, but I'm dubious polymer cases will ever be practical. They just aren't able to beat the metals in the prerequisite combination of strength -and- resilience -and- stiffness -and- low volume. Even if they did, they don't carry significant heat away from the gun, not compared to brass or aluminum.


The plastic cases do not tranfer heat to the chamber and isolate it from the combustion. But I do not know how that influences the whole process of firing a bullet and cycling the weapon. Is the energy transfered to the barrel instead? Does the plastic case just get hot and melt a bit on the inside?


Hot, high-pressure combustion gasses heat and erode the throat of the barrel. This is what causes many heat-related failures. Plastics have both low heat capacity and low heat conductance, so they contribute nothing to cooling.

Edited by TTK Ciar, 19 June 2017 - 1753 PM.


#144 Blunt Eversmoke

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Posted 19 June 2017 - 1428 PM

 

In machine cannons at least there are aluminium cartridge cases in use. mostly in fighter guns. So scalig this down to handheld size is a possibility. I have never thought of titanium for this purpose. Isn't it too stiff (elasticity module) for the purpose of fitting tighter into the chamber on firing?


Scaling down existing large-caliber aluminum cartridges might be possible. It depends. Since stiffness is proportional to the cube of material thickness, a scaled-down aluminum part will exhibit disproportionately lower stiffness. If it is too flimsy to handle the mechanical stresses of loading, something has to change -- either use of an alloy with a higher flexural modulus (which is linearly proportional to stiffness) or increase case wall thickness (so no longer a proportional scaling down of the original), or both.

Shep854 says he's fired aluminum-cased munitions, so I guess they exist. I'm curious to learn what alloy they used for that, whether they have thicker case walls than their brass equivalents (and consequently reduced case volume?), and how much they cost. Maybe the solution is already here?

As for titanium, again it depends on the alloy. Some titanium alloys are quite malleable:

http://matweb.com/se...65498f93cba0959

http://matweb.com/se...bcc4216982c478c

The main trick is bringing down the price. Titanium oxide is very plentiful (Ti is 9th most abundant element in Earth's crust), but cannot be economically reduced. Commercial titanium is reduced chemically from titanium-bearing compounds with high reactivity. This and the controlled environment it requires for alloying make it expensive. A better catalyst than carbon might make titanium smelting feasible (smelting TO2 with carbon makes TiC which is as hard to reduce as TO2). There are a lot of people working on this right now. We'll see if anything comes of their labors.

 

Folks are trying to achieve this now with polymers, but I'm dubious polymer cases will ever be practical. They just aren't able to beat the metals in the prerequisite combination of strength -and- resilience -and- stiffness -and- low volume. Even if they did, they don't carry significant heat away from the gun, not compared to brass or aluminum.


The plastic cases do not tranfer heat to the chamber and isolate it from the combustion. But I do not know how that influences the whole process of firing a bullet and cycling the weapon. Is the energy transfered to the barrel instead? Does the plastic case just get hot and melt a bit on the inside?

 


Hot, high-pressure combustion gasses heat and erode the throat of the barrel. This is what causes many heat-related failures. Plastics have both low heat capacity and low heat conductance, so they contribute nothing to cooling.

 

Minor nitpick: This statement, indisputably true it though is, might invoke the completely false notion that any casing material could actually contribute anything to cooling.

Formulated correctly, none do; instead, some do a more shitty job isolating the chamber from hot gas (especially, aluminum cases do), while others do an ever so slightly less sucky job on that (plastics; not that it mattered any). Tony Williams and also, I believe, some of the resident machinegunners explained it in some length on This Grate Sight™.

 

To make the casing actually contribute to cooling, one would have to find a way of putting some water or some other coolant inside - without corrupting the primers and the powder - from where it could evaporate and push out hot gas residue and make combustion less hot, and it would probably still not be enough of an effect and/or make the ammo far too heavy (and also, maybe, unduly slow combustion down). 



#145 sunday

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Posted 19 June 2017 - 1536 PM

Cooling of the chamber by casing is done by heating the casing, then ejecting it. The heat used in heating the casing is heat that is not used in heating the chamber.

 

Probably the figures tell this cooling is not very much, however.



#146 lastdingo

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Posted 19 June 2017 - 1558 PM

Agreed, it's simple thermodynamics. Cartridge cases cool down the chamber as long as they get into contact (or to be thorough: into line of sight) with it and were cooler before so.

 

The effect could be calculated, though making some assumptions would help a lot.

One could assume that the cartridge stays in the chamber until a certain % of the temperature difference has been eliminated and ignore the cooling of the chamber by other factors in the meantime. One needs only three values for the case and the temperature gradient to do that and would get a good approximation at least for metallic cases (not necessarily for polymer cases, since they would need a long time to heat up).

 

One might even consider the propellant and the percussion charge as heat sinks, too.



#147 shep854

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Posted 19 June 2017 - 1700 PM

To clarify; the aluminum-cased ammo I've fired was pistol ammo, 9x19 and .45ACP, as well as snake shot in .38 and .44Spl.  Rifle ammo is a whole 'nother thing.



#148 Ivanhoe

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Posted 19 June 2017 - 2308 PM

I don't know this type of sight (it looks like a sight for dumb 40 mm rounds), but it seems obvious to me that this guy shows an exaggerated elevation angle.


Not if the US Army is preparing for a well-known foe requiring high elevation angles;
do0501%20Film%20Scene.jpg

#149 shep854

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Posted 24 June 2017 - 1745 PM

Polymer link ammo belts?

http://www.thefirear...m-machine-guns/

 

Polymer Disintegrating Belts for PKM Machine Guns

"According to Ukrainian Industrial Portal, a company called RAROG (Kharkov, Ukraine) has developed a polymer made disintegrating belt for the PKM machine guns. The standard PKM belts are non-disintegrating (the links are connected to each other) and they are made of metal. Polymer construction of the new belt should allow saving some weight."


Edited by shep854, 24 June 2017 - 1748 PM.


#150 lastdingo

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Posted 25 June 2017 - 1703 PM

 

Not content with moaning, Paul has done something quite brilliant, established relationships with a range of excellent speakers like Dr Matt Ford, Lt Gen (Ret’d) Sir John Kiszely KCB MC, Professor Gary Sheffield FRHistS, FRSA, Dr Stuart Mitchell and Dr James Kitchen of RMA Sandhurst, Dr Daniel Todman, with others in the pipeline, to deliver a series of ‘Defence Talks’ at the Prince Consort’s Library in Aldershot.

They start on Tuesday 4th of July with a talk from Dr Mathew Ford, Senior Lecturer in International Relations at the University of Sussex. Matt Ford holds a PhD from the Department of War Studies at King’s College, London and had a very successful career in management consultancy before entering academia. A former West Point Fellow and winner of the Society for Military History’s Russell F. Weigley Graduate Award, Matt has written extensively about military-technical change, especially as it relates to the infantry and their experience of battle. Matt is an Honorary Historical Consultant to the Royal Armouries at Leeds. Matt’s subject is ‘Is it Gucci? What small arms can tell us about the military’s attitude to innovation and adaptation’

 

http://www.thinkdefe...es-talk-series/



#151 bojan

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Posted 05 August 2017 - 2216 PM

99th level of retardness...

http://www.thefirear...leased-us-army/



#152 Simon Tan

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Posted 06 August 2017 - 1055 AM

Mk17.






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