New Chinese Mach 6 Tank Gun?

bobbymike

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China has a new multipurpose cannon (sy_wsh at lt.cjdby.net via Popular Science). The 127th Ordinance Research Institute's news 125mm tank cannon is the world' largest, with a barrel length over 7.5 meters and highly powerful shells.

The multipurpose cannon achieves its high performance through a high length to caliber ratio of at least 60:1 (the longest tank gun in service is the German 120mm cannon, which has a ratio of 55:1), and a larger cartridge, that stores more propellant explosives. While the multipurpose cannon is currently mounted on a towed carriage, several characteristics suggest that it is intended for tank turrets.

This multipurpose cannon reportedly has a muzzle velocity of 2,000 meters per second (almost mach 6) for armored piercing fin stabilized discarding sabot (APFSDS) rounds, whose discarding sabot concentrates the kinetic energy from propellant into frontal area of the penetrator rod, which is the size of a half dollar coin.

* Current Chinese 125mm APFSDS have a 1700 meters per second muzzle velocity
* German L55 has a muzzle velocity of 1,750meter per second
* US's M829A3 APFSDS round has a muzzle velocity of only 1,555 meters per second (but uses a larger penetrator with increased mass to increase imparted kinetic energy).
 

GruntFox

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* US's M829A3 APFSDS round has a muzzle velocity of only 1,555 meters per second (but uses a larger penetrator with increased mass to increase imparted kinetic energy).
This is somewhat misleading. The reason that the M829A3 uses a 1.55km/s velocity isn't because of larger penetrator (it has an effect, but not as much as you would think) but because of the penetrator material being depleted uranium, with 1.55km/s being the 'sweet spot for its various attributes (including, but not limited to, setting everything on fire).

From what I've seen of the weapon, it's suspected to be an L/60+ gun, which is very unusual with our propellant technology.
 

drejr

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* US's M829A3 APFSDS round has a muzzle velocity of only 1,555 meters per second (but uses a larger penetrator with increased mass to increase imparted kinetic energy).
This is somewhat misleading. The reason that the M829A3 uses a 1.55km/s velocity isn't because of larger penetrator (it has an effect, but not as much as you would think) but because of the penetrator material being depleted uranium, with 1.55km/s being the 'sweet spot for its various attributes (including, but not limited to, setting everything on fire).

From what I've seen of the weapon, it's suspected to be an L/60+ gun, which is very unusual with our propellant technology.

The length of a long-rod penetrator is crucially important, and penetration of a given length of DU will continue to increase with velocity until impacts become fully hydrodynamic at over 2 km/s.

While DU begins to lose its advantage over tungsten at higher velocities there's no "sweet spot" against modern armor at 1.55 km/s. This is just the maximum the M256 can fire M829A3 rounds. M829A3 penetrators are ~50% longer and 3mm greater diameter than M829 because this is more important than 200 m/s more velocity against the threat it's designed to face.

Against future threats or different armor higher velocities may be more desirable.

p3weyGM.png


If the effect of mass (which is really rod length) wasn't "as important as we would think" the development of LRPs wouldn't look like this:

qdS8u5FghQavCwKjPMrWDLLsVR-qs9kag3yPS9zlAqY=w658-h577-no
 
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muttly

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Why is tungsten better at higher velocity than DU? I thought that
all that density of the DU was the way to go.
 

_Del_

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Tungsten alloys won't fracture as readily. DU and its alloys will penetrate better --unless the round fractures. Hence the WHA rounds outperforming DU at high velocity.
 

GruntFox

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Why is tungsten better at higher velocity than DU? I thought that
all that density of the DU was the way to go.
There are several interesting attributes at a specific velocity band. In this case, it's around 1.55km/s and DU being self-sharpening and sets everything on fire the moment the material hits the atmosphere (oh, and the shards of DU will also set everything on fire) are some of the properties that nations using DU ammo look for in their use. If you go past that band, you lose on those properties.
* US's M829A3 APFSDS round has a muzzle velocity of only 1,555 meters per second (but uses a larger penetrator with increased mass to increase imparted kinetic energy).
This is somewhat misleading. The reason that the M829A3 uses a 1.55km/s velocity isn't because of larger penetrator (it has an effect, but not as much as you would think) but because of the penetrator material being depleted uranium, with 1.55km/s being the 'sweet spot for its various attributes (including, but not limited to, setting everything on fire).

From what I've seen of the weapon, it's suspected to be an L/60+ gun, which is very unusual with our propellant technology.

The length of a long-rod penetrator is crucially important, and penetration of a given length of DU will continue to increase with velocity until impacts become fully hydrodynamic at over 2 km/s.

While DU begins to lose its advantage over tungsten at higher velocities there's no "sweet spot" against modern armor at 1.55 km/s. This is just the maximum the M256 can fire M829A3 rounds. M829A3 penetrators are ~50% longer and 3mm greater diameter than M829 because this is more important than 200 m/s more velocity against the threat it's designed to face.

Against future threats or different armor higher velocities may be more desirable.

p3weyGM.png


If the effect of mass (which is really rod length) wasn't "as important as we would think" the development of LRPs wouldn't look like this:

qdS8u5FghQavCwKjPMrWDLLsVR-qs9kag3yPS9zlAqY=w658-h577-no
It isn't penetration, but various properties of the material. From what I can gather, once you get out of that 'sweet spot' in terms of velocity, you lose out on things like self-sharpening (which helps with armor penetration) and setting everything on fire. Given how packed in tanks in general are, the latter is pretty critical to maximize a kill.
 

drejr

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It isn't penetration, but various properties of the material. From what I can gather, once you get out of that 'sweet spot' in terms of velocity, you lose out on things like self-sharpening (which helps with armor penetration) and setting everything on fire. Given how packed in tanks in general are, the latter is pretty critical to maximize a kill.

The problem is that this is obviously untrue, because:

1) Projectiles don't pass through armor at constant velocities.
2) Ultimately the adiabatic shearing responsible for both phenomena is a result of pressure, so increasing the sectional density is equivalent to increasing velocity.
3) DU penetrators have been empirically testing at velocities in excess of 2 km/s with no indication of a "sweet spot."

In actuality the M829A3's velocity is a result of maximizing the gun's energy efficiency by increasing the penetrator's L/D ratio and strength (particularly bending stiffness), qualities which are more important than velocity or even material selection (within reason, of course) in determining penetration.

In fact, I bet if you ran the math you'd see the most efficient velocity for any tank gun firing penetrators with an aspect ratio of ~32 would about...1540 meters per second.

So this is kind of a moot point as we'll likely see novel penetrators and perhaps even lower velocities before the widespread adoption of giant Mach 6 tank guns.

PS: The pyrophoric effect of DU LRPs is academic and "self-sharpening" (which is commonly used but doesn't exactly convey what's going on) may be less of an advantage against modern armor arrays than RHA depending on their failure mode.

Why is tungsten better at higher velocity than DU? I thought that
all that density of the DU was the way to go.

The square root density law. As projectiles approach the hydrodynamic limit their mechanical properties become more or less irrelevant compared to their density. Latest hypervelocity research suggests they play some role but it's still uncertain exactly how much.
 
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muttly

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Does that mean that one should think heavier not faster for the penetrators?
 

GruntFox

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It isn't penetration, but various properties of the material. From what I can gather, once you get out of that 'sweet spot' in terms of velocity, you lose out on things like self-sharpening (which helps with armor penetration) and setting everything on fire. Given how packed in tanks in general are, the latter is pretty critical to maximize a kill.

The problem is that this is obviously untrue, because:

1) Projectiles don't pass through armor at constant velocities.
2) Ultimately the adiabatic shearing responsible for both phenomena is a result of pressure, so increasing the sectional density is equivalent to increasing velocity.
3) DU penetrators have been empirically testing at velocities in excess of 2 km/s with no indication of a "sweet spot."

In actuality the M829A3's velocity is a result of maximizing the gun's energy efficiency by increasing the penetrator's L/D ratio and strength (particularly bending stiffness), qualities which are more important than velocity or even material selection (within reason, of course) in determining penetration.

In fact, I bet if you ran the math you'd see the most efficient velocity for any tank gun firing penetrators with an aspect ratio of ~32 would about...1540 meters per second.

So this is kind of a moot point as we'll likely see novel penetrators and perhaps even lower velocities before the widespread adoption of giant Mach 6 tank guns.

PS: The pyrophoric effect of DU LRPs is academic and "self-sharpening" (which is commonly used but doesn't exactly convey what's going on) may be less of an advantage against modern armor arrays than RHA depending on their failure mode.
From what I've seen and been told, tungsten is far more efficient at higher velocities (i.e. approaching 1.8km/s with conventional powders) than DU, which is more efficient at lower velocities. Mind you this is from a site where things are analyzed to the point that it's basically beating a dead horse.
 

drejr

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r
Does that mean that one should think heavier not faster for the penetrators?

"Perhaps." This seems to be one of the directions newer tungsten ammunition is taking but US DU ammo really can't get any heavier except by increasing diameter - which may be necessary against future armor. M829A4 is probably ~100 m/s faster than M829A3 (at least at 21 degrees C) but not much is known about the penetrator.

In the short term LRPs are a mature technology and we probably won't see radical differences in velocity, but things like closer tailoring to specific threats, improvements that aren't obvious on a stat sheet like more stability in the internal and transitional ballistic regimes, and improved materials - for example, depleted uranium's adiabatic shear banding behavior isn't a unique property and can probably be replicated by tungsten alloys with the proper matrix.

In the long term LRPs will probably be replaced by novel penetrators. Some of these may work well at current ordnance velocities, others like highly-segmented penetrators aren't theoretically bound by density laws and can take advantage of radically higher velocities.

From what I've seen and been told, tungsten is far more efficient at higher velocities (i.e. approaching 1.8km/s with conventional powders) than DU, which is more efficient at lower velocities. Mind you this is from a site where things are analyzed to the point that it's basically beating a dead horse.

No. Around 1.8 km/s is when the penetration of a tungsten and DU rod of equal L/D ratio will be roughly equivalent. Tungsten doesn't become "more efficient" by this measure until around 2.5 km/s.

It's true there's an optimal velocity for each material that maximizes penetration for a given energy level against a given target material. This optimal velocity is higher for tungsten than depleted uranium, but exceeding this velocity doesn't decrease penetration, it makes it less energy efficient. This may not be the most important concern.

M829A3 fires a LD ~32 penetrator at 1.55 km/s. This is close to the optimal velocity of DU against RHA and the best use of the available energy.

M829A4 fires a LD ~32 penetrator at 1.65 km/s. This exceeds the optimal velocity but it almost certainly penetrates more, not less because it's out of some "sweet spot." Due to temperature insensitive propellant it has more energy available. If it were to fire a heavier LD ~40 rod (for example) at 1.55 km/s it would be more energy efficient and penetrate even more, but this is beyond the physical limits of the gun and perhaps material technology - which limits L/D ratios.

tanknet and whatever are great but they tend to put too much emphasis on RHAe penetration, which is less and less a measure of actual effectiveness. Actual armor arrays are complex enough that sweeping generalizations are rarely true.
 
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