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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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verong       10/14/2007 10:41:38 PM
Hey Folks,
 
what are the chances the supporting infantry might get hurt?????
 
Sincerely,
 
Keith
 
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Nichevo       10/15/2007 12:26:02 AM


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
Excuse me, Herald, perhaps I was unclear.  I was saying that my own idea of the plates moving to, call it, ten o'clock and four o'clock - instead of one and seven o'clock as now - might better shear the penetrator, but work less well on the shaped charge/EFP.  Or perhaps not, if you say so.  Now that I truncated the quoted message I cannot as readily look it over.

Were it not for the high pressure of the internal explosive, too, I would think the rapidly separating plates might induce a vacuum, which might vitiate the shaped charge.

Another advantage of my scheme, though, is that it might be safer for nearby infantry/dismounts.

 
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Bluewings12       10/15/2007 1:22:29 PM
I read with attention the last 10 posts or so .
 
Dwightlooi has some good points but the rod 's yawn when impacting a good ERA can be as big as 25 degrees . When it happens , the penetration inside the tank is simply impossible . The rod has failed .
Another point is the shock wave generated by the very high velocity impact when the moving plate hit the rod . That alone can break the rod in 4 , 5 , 6 or even more pieces . Because the shock wave is following and travelling through the entire lengh of the rod , the latest can simply be destroyed even before to reach the main armor .
In this regard , Tungsten behave a little bit better than Depleted Uranium .

During testing , people found out that ERA works better at close range than long range (!) . The reasons for that are easy to understand :
1) up to 1400-1500m , the rod follow (fly) in a straight line , almost horizontaly . The angle during impact is perfect for ERA to do a very good job .
2) Faster the rod is , better it is for ERA to also do a good job .

As an exemple , a very slow rod would only loose 1 or 2cm of its tip bcause the moving plate is just flying away too fast , then the shock wave would be minimal . It is why a tank equipped with ERA has to be taken out as far away as possible to allow the rod to slow down and get an almost perpendicular hit {ballistic}(less yawn versus ERA) .

Cheers .


 
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Bluewings12       10/15/2007 1:30:57 PM
It has to be noted that ERA (especially the Russian ones) are built to stop fast moving penetrators , them beings rods or shape charges . Since we all try to get a faster penetrator , it shows how clever the Russians are .
A slow moving cannonball would not be disrupted by ERA ~almost~ but would still bounce on the main armor .

Just put some of the latest Kontakt ERA on top of a tank also equipped with a hard-kill system like ARENA and the mighty TOW-B can be mothballed ...

Cheers .


 
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Herald1234    Test results?   10/15/2007 2:08:32 PM
Assertion needs proof. Oh Beryoza? wherefore art thou? Better yet, Carl S, or Mike Golf?

Herald

 
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Bluewings12       10/15/2007 3:00:35 PM
Herald :
""Assertion needs proof""

That will be difficult because the tests I am reffering to are still classified and cannot be posted here .
Nevertheless , I can still give some explainations by using some other datas .
First , a reminder of what an ERA like Kontakt-5 is (not the latest but already real good) :

""The patent for K-5 shows ERA is a box with K-1 type plates inside. The outer 25mm plates hardly move at all and are fixed in place but there are 2—5 inner plates [similar to K-1] with no more than 2 layers ?active? and the others inert. It might be that, since the ?active? layers are in segments themselves, they are intended to detonate separately -move the plates -like a ?bulging plate?- and be able to ?do it again? when the next projectile hits the next ?segment?, in other words: It might be reusable! Since only a maximum of 2 of the 4-7 plates are ?flyer plates?, the variation should be about  (BW note : Classified) ...""

Now , if you link this info to what I said , you should understand few things ...

Cheers .




 
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Bluewings12       10/15/2007 5:12:23 PM
I am aware that I did not give much But it is difficult for me to help you :-(
Some can understand .
What I can say is in the end of the day , we 're fighting a lost cause regarding actual penetrators versus ERA . Understand that I am not saying that it doesn 't work anymore , but rather that we only have 40% chance to penetrate the latest Russian ERA with our best penetrators and our best ground launched ATGMs have increasingly more difficulties to defeat ERA and hard-kill systems .
China is working on it too .

Irak proved that 1 of the best western MBTs could be penetrated by portable ATGMs (the Abrams) because of lack of ERA and hard-kill systems . The fact that the Abrams has not the best main armor around doesn 't change a thing . In fact , I am a bit wrong because the Chally did survive more hits from portable ATGMs than the Abrams by a big margin .
Kudos to the British Dorchester . That doesn 't mean that the Abrams is a weak Tank , not at all .
It simply means that we must work more on active defenses like the Russian do . I heard that the Chineses are into something but I do not know anything relevant yet .

From now to a near futur ~20 years~ the stopgap is on active defenses . In 20 years time , railguns will be fielded and only electromagnetic fields will be used as active defenses .
Back to square one , same story again ...

Cheers .

 
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dwightlooi       10/15/2007 5:35:36 PM

I am aware that I did not give much But it is difficult for me to help you :-(

Some can understand .

What I can say is in the end of the day , we 're fighting a lost cause
regarding actual penetrators versus ERA . Understand that I am not
saying that it doesn 't work anymore , but rather that we only have 40%
chance to penetrate the latest Russian ERA with our best penetrators
and our best ground launched ATGMs have increasingly more difficulties
to defeat ERA and hard-kill systems .

China is working on it too .


According to whom?

Not according to ATK which claims that the M829A2 specifically defeats the Konkakt-5  and that the M829A3 defeats all known ERA types currently in service with sufficient margins to defeat all projected ERA threats projected for the foreseeable future. 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. That was in 1995.

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% such that (in their opinion) the redisual penetration can be stopped by the front armor of their current generation of tanks.
 
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Jeff_F_F       10/15/2007 7:19:17 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.
 
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Jeff_F_F       10/15/2007 7:31:28 PM

It has to be noted that ERA (especially the Russian ones) are built to
stop fast moving penetrators , them beings rods or shape charges .
Since we all try to get a faster penetrator , it shows how clever the
Russians are .

A slow moving cannonball would not be disrupted by ERA ~almost~ but would still bounce on the main armor .



Just put some of the latest Kontakt ERA on top of a tank also equipped
with a hard-kill system like ARENA and the mighty TOW-B can be
mothballed ...



Cheers .





Based on what BW is saying here the slower/heavier approach long-rod penetrators seems like exactly the correct route, while the lighter/faster approach is just playing into the strengths of the ERA.
 
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