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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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dwightlooi       10/15/2007 9:27:53 PM

At the minimum, note that at long range, the MRM will not be flying horizontally but will be plunging significantly. This means less shear because the upper plates will be moving mor in line with the line of flight of the missile. Turn the blue line downward at an angle in the diagram shown above.

 

The other danger is APS, it occurs to me that with the manuvering abilities needed to hit a hypersonic missile are not needed to hit a tank. However if the projectile has energy to spare due to being rocket boosted it could trade some energy for terminal maneuvering to make it more difficult for an APS system to engage it.

Actually, right now there is no APS which is effective against Long Rods or MRM-KE type threats. It is not just that at Mach 4~5 the target is hard to hit. It is that a dense, solid object doesn't care about the blast wave an APS grenade or for fragmentation damage.

It is very much like the problem with killing ballistic missiles barrelling down on a city at Mach 8 in a near vertical dive. The PAC-2s hit them over 90% of the time in GWI. What happened? They drop down on the city anyway in one mangled piece or in 2~3 pieces anyway. And as far as causing terror to the population it is practically as good as an intact missile.

Now imaging a DU rod or a MRM-KE driving straight for a tank. Pepper it with fragments or pop an APS grenade charge 10cm away from it. Does it matter? Not really, there is no fuse to damage, no warhead to set off, no shaped charge to spoil. Just 7kg worth of depleted Uranium that is going to crash into you anyway. Imagine a DU rod come straight at you at Mach 4.5 and you successfully pepper it with a blast from a 12 gauge shot gun. You should count yourself lucky if you deflect it by 2 inches, and even if you did, does it matter?

 
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KlubMarcus       10/15/2007 10:05:11 PM
American tankers will normally shoot two rounds at a tank. One KE and HE. It won't matter what the enemy has got. They won't survive. American tankers and their tanks have a very high 1st and 2nd round hit percentage. If that doesn't work, the tank behind the forward tank will take the additional shot(s) too.
 
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Jeff_F_F       10/16/2007 12:04:26 PM
Agreed completely on current APS. I'm thinking more in terms of long term development. How long ago was it that there was no way to shoot down any incomming round or missile? It also depends on the range at which the weapon is being engaged at, if it is at 100m, even a 1 degree deflection will likely cause the weapon to miss, or at least to hit a less critical part of the tank.
 
Ultimately no weapon can be designed to defeat current threats because of the long development cycle, doing so is to doom your weapons to always be obsolete when they are fielded. Instead both sides must gamble on what they think the next generation of enemy capabilities will be and start developing weapons now which will defeat them when they are deployed.
 
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Ehran       10/16/2007 12:18:48 PM

. Imagine a DU rod come straight at you at Mach 4.5 and you successfully pepper it with a blast from a 12 gauge shot gun. You should count yourself lucky if you deflect it by 2 inches, and even if you did, does it matter?

if you can displace the nose of the rod 2" off alignment that's actually pretty huge as far as reducing the effects of the rod striking armour.  i'd think it pretty improbable that you could displace the entire rod evenly 2" to the side.

 
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Herald1234       10/16/2007 2:21:09 PM



. Imagine a DU rod come straight at you at Mach 4.5 and you successfully pepper it with a blast from a 12 gauge shot gun. You should count yourself lucky if you deflect it by 2 inches, and even if you did, does it matter?


if you can displace the nose of the rod 2" off alignment that's actually pretty huge as far as reducing the effects of the rod striking armour.  i'd think it pretty improbable that you could displace the entire rod evenly 2" to the side.


Valid point. Not any system that I know we can field on a tank  will displace a slug off trajectory before strike. Rockets? Yes. But not a slug.  Hello railgun.

Herald

 
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doggtag    Ummm...math?   10/16/2007 2:47:28 PM



. Imagine a DU rod come straight at you at Mach 4.5 and you successfully pepper it with a blast from a 12 gauge shot gun. You should count yourself lucky if you deflect it by 2 inches, and even if you did, does it matter?


if you can displace the nose of the rod 2" off alignment that's actually pretty huge as far as reducing the effects of the rod striking armour.  i'd think it pretty improbable that you could displace the entire rod evenly 2" to the side.



If you've got a 30-some inch KE dart coming at you at 1500+m/sec, does pushing its nose 2" in any direction really make that much difference if it's almost on top of you anyway?
Even 2 to 3 feet away when you deflect it by those 2 inches (if you can call it a deflection), that still doesn't much change the fact it's still going to impact you pretty much with most of its energy, mostly intact, still contacting you at one point.
 
As comparing Kontakt's effect mechanism to a pair of scissors in action: remember, scissors won't cut everything (paper is far easier than cardboard), and as your angle of attack changes, you can't cut as well.
Same thing I see in both active and passive armors: deflect the nose of the inbound KE LRP one direction, and it's going to hit at a more oblique angle (farther from an ideal 90° impact), which is good.
But the kicker there is deflecting it away from you rather than inadvertantly deflecting at you (an angle much closer to the ideal 90°).
(this is why ballistic shapes are important, as is avoiding shot traps in a given AFV design).
 
Since it's difficult (impossible altogether?) for any given Automatic Protection System to actually measure an inbound hypersonic LRP's angle of attack (how close to that 90° is it going to hit you?), it becomes difficult to decide that the piece of ERA it hits is going to nullify the impact effect, or enhance it (deflecting it away from you, or encouraging it to bend/flex/divert into you even more?) .
 
The idea of ERA looks fine on paper, and in the case for Kontakt, so long as the inbound LRP in coming at you at an angle favorable to your ERA tile.
But battlefields are not entirely 2D flat surfaces,
which, by the pic of the Kontakt tiles and those drawn arrows, suggests the Russian are anticipating the majority of strikes will always fall within Kontakt's "sweet spot", those angles of attack that favor the ERA mechanism's deflection abilities.
 
Am I missing something?
(sounds to me more like a case for more A-10s with GAU-8s attacking from above, rather than more flat trajectory, horizontally-attacking tank-gun-fired munitions!)
 
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Bluewings12       10/16/2007 2:48:29 PM
""according to ATK which claims that the M829A2 specifically defeats the Konkakt-5""

Well , this is easier said than done . The Kontakt-5 ERA can defeat the M829A1 and the better German DM-53 .
Now when you look at the differences between the A1 and the A2 rounds , there are big on paper but not that big in real life conditions . In fact , the German DM-53 is now rated as good as the M829A2 and could even be better in some cases .
The M829A3 is a different fish ;-) That is an APFSDS !! Unfortunatly , it wears out the barrel and the pressure generated during firing can dammage the breach after a short while .

So , what the Russians are doing to counter that ?
Simple , they are making a better version of Kontakt-5 which is called Kaktus ~which is so far only displayed on the Black Eagle~ and they even have another ERA system but its name is still unknown to the West .
What I know is that the systems are not fielded yet .

""
the M829A3 defeats all known ERA types currently in service with sufficient margins to defeat all projected ERA threats projected for the foreseeable future.""

That is an optimistic guess to say the least .

""
In fact, the M829A2 was specifically tested to defeat konkakt-5 bricks and the turrent front armor of the T-80 out to the effective range of the M256 120mm gun and its fire control system.""

Unfortunatly , this is not the case . Not really ... The A2 can still be totally destroyed by Kontakt-5 in the same way that the DM-53 is . Depleted Uranium can brake and shatter as easily as Tungsten under very high stress .

""
Not according to the Russian themselves which never claimed that their ERA systems neutralizes long rod penetrators, but rather that they reduce their penetration performance by between 20% and 30%""

lol ! Clever Russians ... Don 't believe them ;-)

""
Based on what BW is saying here the slower/heavier approach long-rod penetrators seems like exactly the correct route""

Absolutly . Changing the caliber ~from 42 to 52 or even 55~ is one thing : being able to fire a heavier round at a good speed but in my view this is the lengh of the breach and the propellant who have to improve . We 're ~in the West~ working on it .
But we have a problem , we just cannot say that all we 're going to fire on will be equipped with the latest ERA . What will happen if we fire on a good composite or a good NERA (Non Explosive Reactive Armor) ?
We still need a very high speed rod with a lot of kinetic energy . So , a compromise has to be made .

Cheers .
 
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Herald1234    In the attack defense cycle.   10/16/2007 3:08:42 PM
always go with the physics.

There is nothing that cannot be overburdened. Two shots, if it take two shots.  Or a fatter LRP; or a rocket-boosted LRP;
The point is that the US probably looked at its options and from what I see by the numbers, the Russians may as well thrown their rubles into the air. Rocket-boosted LRP either cannon-launched or pure rocket-boosted kinetic is probably going to carry the SMASH required to reduce a tank to a paperweight. Given enough smash it could still slam into you sideways and kill you just from collision.

F=MA.

7 kg slug at MACH 5+  is the lower bound, but MACH 8+  is about just  ideal.

Herald


 
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dwightlooi       10/16/2007 4:05:05 PM
Bluewings... I think it is you who is being overly optimistic. Heavy ERA like the Konkakt was never extremely effective to being with. The difference between them and earlier "light" ERA is that they actually have some effect on KE penetrators as opposed to none.

The M829A1 itself could defeat Konkakt-5, the problem is that its ability to reliably penetrate the front armor of Russian tanks every time, all the time was compromised by the new ERA blocks. But it happens only some of the time. The A2 basically lengthened and toughen the rod to practically make the Konkakt-5 style ERA largely irrelevant. The A3 goes even further in anticipation of developments in Heavy ERA types.

If you think that it is hard to get a long rod to defeat ERA I think you have it backwards. It is harder to get ERA to degrade long rods. What happened was that some degree of success was seen and the Long Rod ammunition manufacturers responded to once again push the threshold way back.

 
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dwightlooi       10/16/2007 4:15:18 PM

always go with the physics.

There is nothing that cannot be overburdened. Two shots, if it take two shots.  Or a fatter LRP; or a rocket-boosted LRP;
The point is that the US probably looked at its options and from what I see by the numbers, the Russians may as well thrown their rubles into the air. Rocket-boosted LRP either cannon-launched or pure rocket-boosted kinetic is probably going to carry the SMASH required to reduce a tank to a paperweight. Given enough smash it could still slam into you sideways and kill you just from collision.

F=MA.

7 kg slug at MACH 5+  is the lower bound, but MACH 8+  is about just  ideal.

Herald


Actually the current slugs aren't that fast. The M829A3 is about 1550m/s at the muzzle and at 7 kg for the penetrator itself that is about 16.8 Megajoules. Downrange, after losing about 1/3 of its velocity (down to about 1000m/s) it is about 7 Megajoules.

The DM63 is about 1750 m/s at the muzzle and at ~5kg it is about 15.3 Megajoules. At about 1150 m/s downrange, it is about 6.6 Megajoules.

That is the context we are talking about as far as long rods are concerned. 1000~1150 m/s in impact velocity is about Mach 2.8~3.3.

 
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