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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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flamingknives       10/14/2007 3:45:41 PM
Herald,

The application of lateral force on a LRP (if we must descend to TLAs) is time dependent, but it still has little to do with material strengths. Mass is more significant, so yes, a thicker penetrator with a similar density will be more resistant to advanced ERA. But, all else being equal, the tensile strength is not significant.

The terminology that I am familiar with describes shaped charges as generating a high-velocity jet and a slower (relatively speaking) slug. The jet, due to its prodigeous velocity, does the bulk of the penetration, and being low mass, is comparitively easy to disrupt.
 
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Herald1234    Point of clarification?   10/14/2007 4:09:26 PM
Please explain to me how snapping a rod in two does not bear directly on the rod's material tensile strength, FK?

Herald

 
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Nichevo       10/14/2007 4:48:42 PM
Please note that stubby is perhaps not the term.  Apparently the US LRP is not only thicker, but also longer, as described above.  So the proportions may or may not be changed very much.

It stands to reason that a thicker penetrator is stronger in shear.  But what I would say is that Vmax is reaching a limit - even with more propellant, there are limits on how fast the sabot can travel.  Thus I think they are finding it easier to deliver more energy, and/or momentum, through a heavier penetrator at similar velocities - it is easier to make 2x mass travel at 1x speed than to make the same mass travel at 2x speed, or even sqrt(2)x speed.

Meanwhile, I had not known that reactive armor tries to apply an orthogonal or perpendicular force.  If it does not, then it will do little against a sabot round, I think.  If it does, I would be interested to know the mechanism.

Also, to quibble - the Munroe effect indeed refers to shaped charge.  I thought I had understood that EFPs/SFWs were a slightly different principle, though.

 
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Herald1234       10/14/2007 5:59:23 PM
It is a quibble, the generic class effect is named after the USN yoyo, Charles Munroe, who discovered that you can blast lettering into metal using shaped [directed vector] explosive charges back in 1888 or thereabouts.

You can use ERA to swat, snap, or pinch LRPs; it just depends on how you rebound the plates, or shape the blast waves.

Herald

 
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dwightlooi       10/14/2007 6:13:21 PM

....

Meanwhile, I had not known that reactive armor tries to apply an orthogonal or perpendicular force.  If it does not, then it will do little against a sabot round, I think.  If it does, I would be interested to know the mechanism.
....


Not exactly perpendicular of course, but the mounting of heavy ERA are purposefully set such that the long rod or HEAT jet will tend to contact the ERA steel plates at a very shallow angle. When the explosive fill blows, the front and back plates act as a pair of scissors acting in a shearing action against the penetrator.

If the penetrator isn't robust enough, the ERA shears off about 50 to 100mm of the rod the moment the rod comes into contact with both the advancing front plate and the static (or slowing retreating) rear plate. This causes three detrimental effects. (1) The penetrator is now shorter and hence less effective. (2) The tip is now no longer a spitzer point but rather that of a stick cut at a 20~30 degree angle. (3) A tiny amount of yaw 1~2 degrees may be imparted to the dart causing it to impact with its axis at a slight angle from the direction of flight.

This is easiest to understand if you look at the real thing and how it is mounted. The following is a photo of a Konkakt style ERA on the turret front of a T-80. I think it is self explanatory.

http://img156.imageshack.us/img156/7582/konkakt5actionza3.jpg">

All of the above is mitigated or neutralized if the the long rod is thicker, heavier, tougher and longer. Basically, think of it this way... it is a lot harder to cut or yaw a stout nail compared to say a sewing needle. Velocity and energy of the dart -- while devastating on traditional armor -- offers to improvement in performance against heavy ERA.

 
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Nichevo       10/14/2007 7:26:34 PM

It is a quibble, the generic class effect is named after the USN yoyo, Charles Munroe, who discovered that you can blast lettering into metal using shaped [directed vector] explosive charges back in 1888 or thereabouts.


Very well, so the same shaped charge will at a certain configuration form the EFP, I take it. 





You can use ERA to swat, snap, or pinch LRPs; it just depends on how you rebound the plates, or shape the blast waves.

Herald

I recall Wiki and the explosive printing of the guncotton's trademark.  But when you describe it in this fashion, why do I think of Miznay-Shardin(sp)?

 
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Nichevo       10/14/2007 7:34:27 PM



....

Meanwhile, I had not known that reactive armor tries to apply an orthogonal or perpendicular force.  If it does not, then it will do little against a sabot round, I think.  If it does, I would be interested to know the mechanism.
....



Not exactly perpendicular of course, but the mounting of heavy ERA are purposefully set such that the long rod or HEAT jet will tend to contact the ERA steel plates at a very shallow angle. When the explosive fill blows, the front and back plates act as a pair of scissors acting in a shearing action against the penetrator.

If the penetrator isn't robust enough, the ERA shears off about 50 to 100mm of the rod the moment the rod comes into contact with both the advancing front plate and the static (or slowing retreating) rear plate. This causes three detrimental effects. (1) The penetrator is now shorter and hence less effective. (2) The tip is now no longer a spitzer point but rather that of a stick cut at a 20~30 degree angle. (3) A tiny amount of yaw 1~2 degrees may be imparted to the dart causing it to impact with its axis at a slight angle from the direction of flight.

This is easiest to understand if you look at the real thing and how it is mounted. The following is a photo of a Konkakt style ERA on the turret front of a T-80. I think it is self explanatory.

http://img156.imageshack.us/img156/7582/konkakt5actionza3.jpg">

All of the above is mitigated or neutralized if the the long rod is thicker, heavier, tougher and longer. Basically, think of it this way... it is a lot harder to cut or yaw a stout nail compared to say a sewing needle. Velocity and energy of the dart -- while devastating on traditional armor -- offers to improvement in performance against heavy ERA.

Interesting indeed.  I had assumed the plates were more conformal, and not so large in area.  You could further, as Herald I think is saying, configure the blast somehow (with tamped or shaped charges?!?) either to deflect the sabot at an even more advantageous angle,

or, as was my thinking, to drive the front/back plates LATERALLY to really shear or deflect the long rod.  Imagine if that top plate was blasted up and to the left, instead of out.  And the back plate could go either the same way, or perhaps better, the other way (also maybe easier to engineer, both plates reacting in opposition).

This might or might not work so well against shaped charges, perhaps.
 
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Nichevo       10/14/2007 7:36:40 PM
Also, as for reshaping the tip, we use DU, which is self-sharpening, IIRC.  This would work better against tungsten.
 
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verong    mount on armored humvee   10/14/2007 10:21:35 PM
Hey Folks,
 
Why can you not use a tubular support system to absorb the recoil and transfere it into the suspension system or a plate mounted on  the humvee like electrical workers use to balance while in the buckets??? I no that would mean you have to stop to fire, but currently the 82nd and 101st have no armor of any kind, and this system would be air mobile and air droppable.
 
Sincerely,
 
Keith
 
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Herald1234    Dwightlooi and I are saying exactly the same thing.   10/14/2007 10:34:52 PM







....

Meanwhile, I had not known that reactive armor tries to apply an orthogonal or perpendicular force.  If it does not, then it will do little against a sabot round, I think.  If it does, I would be interested to know the mechanism.
....




Not exactly perpendicular of course, but the mounting of heavy ERA are purposefully set such that the long rod or HEAT jet will tend to contact the ERA steel plates at a very shallow angle. When the explosive fill blows, the front and back plates act as a pair of scissors acting in a shearing action against the penetrator.

If the penetrator isn't robust enough, the ERA shears off about 50 to 100mm of the rod the moment the rod comes into contact with both the advancing front plate and the static (or slowing retreating) rear plate. This causes three detrimental effects. (1) The penetrator is now shorter and hence less effective. (2) The tip is now no longer a spitzer point but rather that of a stick cut at a 20~30 degree angle. (3) A tiny amount of yaw 1~2 degrees may be imparted to the dart causing it to impact with its axis at a slight angle from the direction of flight.

This is easiest to understand if you look at the real thing and how it is mounted. The following is a photo of a Konkakt style ERA on the turret front of a T-80. I think it is self explanatory.

http://img156.imageshack.us/img156/7582/konkakt5actionza3.jpg">

All of the above is mitigated or neutralized if the the long rod is thicker, heavier, tougher and longer. Basically, think of it this way... it is a lot harder to cut or yaw a stout nail compared to say a sewing needle. Velocity and energy of the dart -- while devastating on traditional armor -- offers to improvement in performance against heavy ERA.


Interesting indeed.  I had assumed the plates were more conformal, and not so large in area.  You could further, as Herald I think is saying, configure the blast somehow (with tamped or shaped charges?!?) either to deflect the sabot at an even more advantageous angle,

or, as was my thinking, to drive the front/back plates LATERALLY to really shear or deflect the long rod.  Imagine if that top plate was blasted up and to the left, instead of out.  And the back plate could go either the same way, or perhaps better, the other way (also maybe easier to engineer, both plates reacting in opposition).

This might or might not work so well against shaped charges, perhaps.
Look at the plates and imagine how those plates bounce out and in as the explosive goes off.

The blast wave itself can travel through a molten amorphous jet and deshape it. If it causes nothing more than a slight yaw it would disrupt the jet..

Herald
 
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