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Subject: Revolution in American Tank Gun and Ammunition
dwightlooi    10/13/2007 6:20:10 PM
The revolution in American Tank Gun and Ammunition

For much of the 1970s and 1980s, American tank gun ammunition development has been pretty much a mirror of similar developments by European allies. In fact, the US adopted first a British gun (L7A1) then a German gun (M256), firing similar APFSDS ammunition as those used by European armies except for the US preference (partly due to material availability) for Depleted Uranium penetrators while European armies preferred Tungsten alloys. However, this changed in the last decade as philosophies between American and European developers diverged in response to the latest threats.


American tank gun philosophy

The current direction of American tank gun and ammunition development differs from European practices in three different ways. First, America now favors a SLOWER, heavier long rod penetrator over one with the highest muzzle energy and velocity. Second, America has no intent or desire to adopt longer, heavier barreled weapons similar to the Rheinmetall 120mm/L55 or the Giat 120mm/L52, in fact the next generation gun being developed is an L43 weapon that is one caliber shorter in barrel length and lighter than the current 120mm/L44 on the Abrams MBT. Lastly, America has developed a taste for 12km range tank gun ammunition for use with third party designation or autonomous homing guidance.


The Slower, Heavier Rod

The latest sabot round fielded by the US Army is the M829A3. This round fires a long rod that is the longest possible for the legacy 120mm cartridge dimensions with the rod spanning the maximum allowed cartridge length right down to the front of a newly shortened ignitor cap. The 7kg, 924mm long, penetrator is longer, larger in diameter and heavier than that used in say the contemporary German DM63 ammunition (5kg, 745mm long). This long rod round however has a rather low muzzle velocity amongst modern Sabot rounds -- at 1550 m/s it is about 200m/s slower than the German DM63 for instance. But, the 10kg the projectile one heavy slug with the penetrator itself being much thicker in diameter in addition to being longer and heavier than european designs. Its manufacturer, ATK, believes that the round offers similar penetration performance shot out of a 44-caliber barrel as the latest German ammunition shot out of a 55-caliber tube. In addition, the design is believed to be much more resilient to the shearing action of "heavy" reactive armor and is designed to penetrate all existing Konkat style armor with negligible or no degration to penetration performance.

M829A3 - Depleted Uranium APFSDS-T round
http://img151.imageshack.us/img151/1598/m829a3ke8.jpg">

DM63 - Tungsten APFSDS-T round
http://img151.imageshack.us/img151/751/dm63ne0.jpg">


The Shorter, Lighter Gun

Almost in direct contradiction to the European tank gun trend towards longer, heavier 52~55 caliber weapons such as the Giat 120mm/L52 on the Leclerc and the Rheinmetall 120/L55 on the Leopard 2A6, the latest US gun being developed is lighter and a tad shorter than the 120mm/L44 M256 weapon on the Abrams MBT. The XM360 will be roughly 43 calibers long and weigh a paltry 4100 lbs for the entire gun system. This puts it at less than half the weight of the Rheinmetall 120/L55 mounting (9100 lbs). This is partly driven by the desire to make a 120mm weapon available to light FCS vehicles being developed (20~35 tons) and partly due to the believe that the next major step up in tank gun lethality cannot be had with longer and heavier guns anyway. For instance, the Rheinmetall 120/L55 fires the DM63 ammunition with 7% more velocity and 15% greater impact energy than the same round fired from a Rheinmetall 120/L44. While this is no doubt a tangible improvement it neither dramatically improves lethality nor offer a tangible increase in effective engagement range. The next major leap in tank gun lethality will have to come from somewhere else.

http://img401.imageshack.us/img401/6659/xm360m256cg5.jpg">
http://img401.imageshack.us/img401/3325/xm360ja0.jpg">
http://img401.imageshack.us/img401/9245/xm360firingrz6.jpg">


The Guided Medium Range Munition (MRM)

The US is currently developing two guided, rocket assisted anti-tank rounds with a range of 12 km. In some ways these are similar to gun launched missiles such as the MGM-51 and those used by Russian tanks. The big difference is that unlike other ATGMs, these are launched at full
 
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doggtag       10/14/2007 12:28:54 PM

Even at Mach 8 (about 2.6km/s at sea level), you still need mass to have an effect. There are systems on satellites that will stop 10km/s+ particles, because they're small.

Since ERA works on shaped charge jets, which range in speed (within the jet) from 2-8km/s, I think that the liklihood of a projectile going fast enough to avoid ERA is small. 

See where you're getting at with that assumption, but...
As the speed of KE LRPs continues to increase (saw somewhere the 120L55 pushed tungsten out at 1900m/sec),
the reaction time of the ERA's detonation effect will have to increase accordingly.
All the KONTAKT in the world means nothing if its ideal detonation condition doesn't function fast enough to disrupt the LRP.
 
It's kind of like the hit-to-kill principle used in intercepting ballistic missiles: you get to a certain point where the velocities in question are just too fast for chemical explosives to counter (both the explosion initiation and the resultant blast wave aren't fast enough to match the velocity of all the KE stuff moving at such high velocities).
 
So unless AFVs start sporting 360° radar coverage systems that can locate inbound projectiles fast enough, and sufficiently fast enough electronic brains to activate the ERA or proactive armor device soon enough to be at the ideal disruptive pattern when the KE projerctile impacts, then you might as well not even waste the expense on equipping with additional armor.
Getting hit with a Mach 8+ theoretical LRP: measure that in feet per second, it's like almost 9000feet per second. Any countermeasures device that must effectively nullify that projectile will have milli microseconds to react and select the appropriate armor panel to predetonate sufficiently early enough to generate an effective disruptive pattern far enough ahead of the LRP to disrupt its flightpath to the point it isn't dumping its M8+ KE into you at a single point.
The other issue there is, still getting hit by less-than-Mach-8 bits and pieces is still going to cause considerable external damage: sights & optics, barrel, hatches, engine decking, etc, any areas that aren't designed to withstand direct hits by LRP s will be compromised.
So unless your KE countermeasures system can fully divert, by whatever means, a supervelocity penetrator completely away from your vehicle altogether, then the faster KE weapons get the less reasoning you have to even try dissipating or redirecting its inbound energy.
When we get to that point, we'd be better suited with the ability to remain undetected to begin with, or hope we can detect the other guy's AFVs before he detect ours and we start launching M10+ KE LRPs at him before he launches them at us.
 
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Bluewings12       10/14/2007 12:57:05 PM
""As to BW's assertions about a current American rocket-boosted LRP getting through KONTAKT""

uh ? Where did I say that ? I said :
I 've noticed one error in the article when it says about the M829A3 that the round ""is designed to penetrate all existing Konkat style armor with negligible or no degration to penetration performance."" That is wrong and over optimistic .

I am not talking about
a rocket-boosted LRP .
Could you read properly next time Herald ? Thank you .

Cheers .


 
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flamingknives       10/14/2007 1:12:36 PM
'Scuse me, but when did tensile strength have much to do with hydrodynamic impact?

Plus, of course, you don't try and stop the tip striking, you aim to shatter the rest of the rod so it doesn't carry its energy into the hole started by the tip. Same deal as with shaped charge, unless you choose to believe that it can disrupt a jet tip at 8km/s and not a slightly thicker rod at less than a quarter of the velocity.

However, as long as you have the mass you can overmatch any armour, or render the armour irrelevant by simply dumping so much energy into the target that you wreck everything sensitive in it, knock the turret off its bearings, whatever.
 
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dwightlooi       10/14/2007 1:17:27 PM

Very good article . Long range kills are indeed the futur but the USA are not the only Country to work on the technology ...



I 've noticed one error in the article when it says about the M829A3 that the round ""is
designed to penetrate all existing Konkat style armor with negligible
or no degration to penetration performance."" That is wrong and over
optimistic .



Cheers .
Actually, that is the basic mission of the M829A3 round over the M829A2/A1.

Unlike HEAT jets, the long rod cannot be dissipated or disrupted for the most parts, the only reason "heavy" ERA like the Konkat family even works to some extent against kinetic energy darts is that the explosively driven plates driven at a perpendicular angle to the substantive external casings stands a chance of shearing off the tip of the penetrator. Its like trying to cut a nail with a pair of scissors though and it is not easy. If the ERA succeeds, it reduces the penetrating performance by physically shortening the rod and also weakening the rod's structural integrity (especially around the now broken front) causing it to sometimes shatter on impact. However, if the rod is robust enough not to break at all when confronted by the heavy ERA's shearing action there is basically no reduction in its penetration performance. Even if it did break, a thick 924mm rod with about 20% cut off is still almost as long as a traditional long rod penetrator and the thick, robust, structure is much less likely to shatter when it drives into the main armor.


 
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Herald1234       10/14/2007 1:17:35 PM

Very good article . Long range kills are indeed the futur but the USA are not the only Country to work on the technology ...



I 've noticed one error in the article when it says about the M829A3 that the round ""is
designed to penetrate all existing Konkat style armor with negligible
or no degration to penetration performance."" That is wrong and over
optimistic .



Cheers .



Point noted.

Herald
 
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Wicked Chinchilla       10/14/2007 1:26:33 PM
Thanks for all the good info, I now have a much better understanding of what is at work.

In short, they are upping the mass of the rod at the expensive of velocity because a heavier LRP is harder to disrupt?
 
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Herald1234       10/14/2007 1:28:19 PM

'Scuse me, but when did tensile strength have much to do with hydrodynamic impact?

Tensile strength directly relates to SHEER force. I assume you thought I confused this with COMPRESSION?   Nope. These factors of worik you do upon the rod, are independent of the  impact event insofar as you try to displace or scatter the work SIDEWAYS at the moment of strike, not VERTICALLY. Vectors and effects are discretely different..

Plus, of course, you don't try and stop the tip striking, you aim to shatter the rest of the rod so it doesn't carry its energy into the hole started by the tip. Same deal as with shaped charge, unless you choose to believe that it can disrupt a jet tip at 8km/s and not a slightly thicker rod at less than a quarter of the velocity.

 I suggest you will find the behavior of a fluid to be far more susceptible to  lateral  displacement [SHOVE] than a solid-especially  a COMPRESSED solid.

However, as long as you have the mass you can overmatch any armour, or render the armour irrelevant by simply dumping so much energy into the target that you wreck everything sensitive in it, knock the turret off its bearings, whatever.

That was the point that I wish I had written, but that others covered quite nicely.

Herald


 
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Herald1234       10/14/2007 1:42:27 PM

Thanks for all the good info, I now have a much better understanding of what is at work.


In short, they are upping the mass of the rod at the expensive of velocity because a heavier LRP is harder to disrupt?

Dwightlooi provided the most clear answer, but the one syllable word answer is that if you are dense, massive, fast and somewhat stubby, you will smash better, than if you are dense, faster, skinnier, and less massive. At some point you have to deal with the armor schemes that attempt to introduce a sideways shove into your vector line, and what worked at Jutland for the British still works for us today. Gravitation, aerodynamics, and kinetics does not like the German solution.

Herald
Herald
 
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flamingknives       10/14/2007 2:33:43 PM
Herald;

I didn't confuse anything. With hypervelocity impact and hydrodynamics and material strength (tensile, compressive or shear) are not generally significant and certainly do not follow any conventional wisdom gleaned from low velocity phenomena.

The interesting thing about a shaped charge jet (and it took reference to a couple of texts to convince me of this) is that it is a solid. It isn't a gas, plasma or even molten. Granted it's a fluid, but because the hydrostatic yield of the liner has been exceeded by the explosive rather than any heating effect. If a shaped charge can turn a solid, heavy metal cone inside out and propel it forward at many km/s, all in a fraction of a second, I think that they can deal with imparting a bit of sideways force to disrupt a long rod. 

That's not to say that you cannot make a long rod more resistant to ERA, and heavier rods are one way of doing it. 
 
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Herald1234       10/14/2007 2:49:49 PM

Herald;

I didn't confuse anything. With hypervelocity impact and hydrodynamics and material strength (tensile, compressive or shear) are not generally significant and certainly do not follow any conventional wisdom gleaned from low velocity phenomena.

Well actually you did. You just conceded that the SHOVE has little time to act on the LRP.

The interesting thing about a shaped charge jet (and it took reference to a couple of texts to convince me of this) is that it is a solid. It isn't a gas, plasma or even molten. Granted it's a fluid, but because the hydrostatic yield of the liner has been exceeded by the explosive rather than any heating effect. If a shaped charge can turn a solid, heavy metal cone inside out and propel it forward at many km/s, all in a fraction of a second, I think that they can deal with imparting a bit of sideways force to disrupt a long rod.

Again you are wrong. The descriptor you are looking for in describing a molten jet formed by the Munroe Effect is AMORPHOUS generally confused with 'glass-like'. In its molten amorphous state, the molten mass does indeed behave like a slug, but only in  the direction of momentum.  It is still far more easily disrupted by pinch or SHOVE forces because of its weak electromagnetic bonding at those plasma like temperatures, than an electromagnetically bonded SOLID which is what an LRP, despite all the compressive forces exerted upon it [in many cases sufficient to reduce its length by up to 25%+ length], is.

That's not to say that you cannot make a long rod more resistant to ERA, and heavier rods are one way of doing it.

It probably would be more technically correct to say thicker in cylindrical chord [stubbier], but your last point is well expressed.


Herald
 
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