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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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earlm       10/13/2007 10:07:06 PM
The US did the same thing with battleship and cruiser AP shells.  There are several advantages to the heavier slower AP projectile.  The long rod is basically approaching obsolescence anyway.  The future is top attack although rocket and ramjet boosted long rods may prolong their lifetime.  The US is way ahead of the rest of the world in recognizing that the end of the gun/armor cycle is approaching.  I think FCS opponents don't realize that.  MRM type projectiles that can perform top attack are the future.  The cycle of competition will be missile and seeker vs stealth, countermeasures, and APS instead of projectile/armor.  Really almost no need for a gun barrel, just use missiles.
 
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verong       10/13/2007 10:27:24 PM
let put it on a upgraded humvee!!!! the heavy humvee has a 2.25 ton cargo capacity which is 4500lb!!!!
 
Sincerely,
 
Keith
 
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earlm       10/13/2007 11:02:40 PM
The recoil force of a 120mm gun is so large that even with a muzzle brake and LRF mounting a humvee cannot handle it.  Also, putting a humvee in a direct fire fight with MBTs is not a good idea.
 
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dwightlooi       10/14/2007 2:20:44 AM

let put it on a upgraded humvee!!!! the heavy humvee has a 2.25 ton cargo capacity which is 4500lb!!!!

 

Sincerely,

 

Keith

I doubt it. A Stryker can probably take one though...



 
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Bluewings12       10/14/2007 6:51:44 AM
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 .

 
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Wicked Chinchilla       10/14/2007 10:15:08 AM
Tanks are not quite my forte' but I was under the impression that Long Rod Penetrators were unaffected, or affected very little, by reactive armor anyway.  I had thought reactive armor was only truly effective versus HEAT-style rounds.  That makes sense in my mind in the style by which they penetrate the armor, molten stream versus sheer power. 

Apparantly I am wrong, anyone care to explain this to me?

 
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flamingknives       10/14/2007 10:23:10 AM
All ERA, AIUI, works by shearing the penetrator, so the impact is spread out over a larger area. This works on both shaped charge jets and long-rod penetrators. Early ERA was ineffective against long rods because the projectile was too massive. The jet, on the other hand, is much lighter but travels much faster (up to 8km/s, compared to 1 - 1.5km/s for the long rod) The low mass means that it is easier to disrupt.

More advanced ERA, however, has large metal plates on the outside and it is the explosively driven motion of these that can disrupt both shaped charge and long rod penetrators. What they will not work on is EFPs, as these solid slugs are just mass at speed - they have no special structure to disrupt.
 
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Herald1234    Physics.   10/14/2007 10:57:07 AM

Tanks are not quite my forte' but I was under the impression that Long Rod Penetrators were unaffected, or affected very little, by reactive armor anyway.  I had thought reactive armor was only truly effective versus HEAT-style rounds.  That makes sense in my mind in the style by which they penetrate the armor, molten stream versus sheer power. 

Apparantly I am wrong, anyone care to explain this to me?

If your explosive panels are offset far enough and designed correctly, when the explosive panel detonates, the LRP can be made to snap in two and TUMBLE as the bolt strikes the working face of the main armor plate. This changes the vector line, scatters the potential work across a larger strike area and redistributes the SMASH across the entire plate instead of allowing it all to concentrate.at a point.

As to BW's assertions about a current American rocket-boosted LRP getting through KONTAKT [although CKEM  testing results probably suggests that he can't justify his assertion at all? I would need to see his data.].  NED about the gun rounds being described actually. But at some point, if a projectile smashes into you at a velocity  within a quarter of the working velocity of the explosive in the ERA panel the rod will NOT suffer displacement, or snap; and it will blow right through the effect; as if the ERA isn't even there. Then you need something else like void offset snapoff panels, or capacitor charged plate  to cause the tumble and snapoff of the LRP you want, as it strikes.

At some point you can make a projectile fast emough that will defeat an object as massive as a huge building and defended by armor RHA standard more than three meters thick. Mach 8+ should just about do it. The means of defense then turns  to active intercept and active/passive deception.

The Russians and Israelis, not being stupid, started working on this particular attack/defense avenue ten to twenty years ago. The US started working on counters to that, ten years ago, and this time: the Europeans who are usually the world leaders in this avenue of the attack/ defense cycle goofed and are playing catchup. They are behind then eight ball. The4 55 caliber gun-tube adaptation is a stopgap  until they come up with their own DF solutions.

Herald
 
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flamingknives       10/14/2007 11:47:59 AM
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. 
 
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Herald1234       10/14/2007 12:11:49 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. 
Working mass is a given, that I assumed would be self evident. bumper shields work at micron particle size because at 7kps or greater the particle actually vaporizes upon strike essentially cratering on the copper. At 5 kg mass or up you get a kinetic kill that either would reduce the ISS to confetti or punch a fist-sized hole right through it depending on how soft the material the impactor composition was.

The projectile moving at 2000 meters per second and the ERA panel working at 10,000 meters per second gives you 10-18x  sheer force to tensile strength to work on a DU rod for what? 1/20,000th of a second before the LRP point digs into the plate? Not enough TIME to laterally displace the following SOLID mass.

Herald

 

 
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