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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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Tbolt       10/22/2007 12:51:14 PM
After reading all the posts from some very smart people my view as a retired tank crewman. One thing is obvious to me when your about to fight the first thing you hit the enemy with is indirect fire so if you hit the tanks with AP submutions destroy the majority of the Konkat armor problem solved. But what do i know im just an old  tanker so start picking my idea apart.
 
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Bluewings12       10/22/2007 5:09:41 PM
Excellent post Tbolt ! Indeed , AP submunitions do the trick .
A nice ICM barrage is a nightmare for any Tank crew .
But this is not what we 're talking about ...

Herald , I really would like to know where I was wrong as you said . Maybe I wasn 't clear enough or maybe I miss something ?
Something else is setting my "alarm" button on . You say :
""US average tank fleet FCS considers that in the range solution sets by using a MEAN solution""
While I can understand the thinking behind the idea , the idea itself would only make sense for someone who doesn 't have a good ammo . Think about it ... Why to give the gunner a "handicap" (limitation) of 4000m when he has ammo who can kill the average joe tank at 5000m ???

Then you go :
""
The US system selectively tosses out the values the computer decides are not valid""
What do you mean by "not valid" ? Are you talking about distances ? You cannot talk about multiple returns because the LRF always gives multiple returns (unless you lase at a Chopper , hehe) .

You also say something true :
""
Yields similar accuracy results over the same EXACT MER ranges""
I agree . Nevertheless , nowadays every tank gun in the World (even the bad ones) can hit a tank at 3000m .

Regarding the FCS , you say :
""
The US system defaults at 4000 meters""
Nice to have you onboard Herald :-)

""
it does not mean you can't shoot""
Of course not , fortunatly ! You have to go manual and guess your superelevation as well as the lead if the target is moving , not an easy business .

But going manual because of a failure is a pain in the butt and adding the lead and range manualy in real time while aiming at a tank who goes diagonaly towards you all gun blazing  is a fuc***g no-no scenario , lolol !
I 've been in the situation many times during drills ;-)

Herald , this I do not believe :
""
US gunnery tables inputted are ballistically matched to armor penetration kill reach which as I wrote above is defaulted at an arbitrary MER per type round selected.""
Again , or the US Army are underestimating their ammo (they are not) , or they are stupid (they are not) .
So , what 's your point ???

""
The beam, itself, is relatively narrow.""
Not really , with the Abrams LRF , at 2500m the beam is almost as big as a tank . At 3000m , you start to get some wrong returns/readings from the ground in front of the target or from the far away landscape (good use of the LRF switch is needed) and at 3800m you sometimes have to lase multiple times to get an accurate firing solution (don 't burn the LRF for God sake !) .

Cheers .
 
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Herald1234       10/22/2007 5:33:47 PM
Look BW.

You can fantasize about optics all you want but a laser that is atmosphere piercing is not going to scatter [spread] the way you claim it does. COLLIMATED light has no charge to cause divergence, as it consists of photons which is a nearly massless EM boson . The only gross scatter mechanism for a photon beam at those short ranges is absorption and re-emission. An atmosphere piercing laser is by design intensely resistant to that mechanism until it hits true opacity that either converts the photon beams energy to heat via spot kinetic energy absorption or photon re-emission and reflects or refracts the beam as scatter upon strike.

As for my description of the gunnery table algorithms and supporting software that sets the gates and select limiters ; I gave my sources.

Have a nice day.

Herald

 
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andyf       10/23/2007 11:40:44 AM
youve got the problem of mechanical failure of the round itself as well on impact
the armour being hit by the LRP is equivalent to the LRP being hit by the armour
this fatter bolt would resist that a lot better
like an FMJ vs a Glaser round
 
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tenX    Laser rangefinser divergence   10/23/2007 7:58:43 PM
Actually, Lasers DO diverge and require collimating optics to control divergence.  There is an inverse square relationship between the collimated beam diameter and divergence.  This is why you see very large telescopes on the various laser weapons.

TenX

 
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Herald1234       10/23/2007 8:13:19 PM

Actually, Lasers DO diverge and require collimating optics to control divergence.  There is an inverse square relationship between the collimated beam diameter and divergence.  This is why you see very large telescopes on the various laser weapons.

TenX


"http://www.fas.org/man/dod-101/navy/docs/laser/fundamentals.htm"

Final focus and aiming and thermal blooming for HIGH POWERED CW lasers.

Herald
 
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Tbolt       10/23/2007 9:04:35 PM
Thanks for the kind words Bluewings but i will still stand by my statement it dosent matter if you have long rod or short penetrators if you can get rid of the armor you can hit them with a big rock. On the lazers on the M60A3 only the tank commander saw the range if you got 9995 for the range you did a sixpack you hit the zero button and reset button the zero cleared all readings and the reset opend the mirrors to full open, so if you had despersion you had a better chance of a good range. On the M1 and M1A1 the gunner could chose first return or last return and for me as a gunner and later as a tank commander part of setting up my fire plan was to observe what the terrain and any folage there was between me and the kill zone if i had tall grass shrubs etc i would chose last return knowing that if lazing a tank it would give off the strongest return, and if shooting over open flat ground first return was chosen. And smoke, dust or fog never had any effect on our shooting the only problems we ever had was pouring rain and heavy sand storms. Just a tankers view you guys are way smarter than me on the tech stuff but dont over think things start with the most obvious and thats usuall as far as you need to go. Tbolt
 
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Bluewings12       10/24/2007 12:13:14 PM
Herald is wrong and TenX is right .

Low powered lasers ~like the ones used on Tanks~ do diverge and spread over distance .
I quote again :
""Although the pulse of laser light is a focused beam, this beam does widen over distance. At a range of two or three kilometers, the beam will be spread out so much that a tank might NOT block the entire beam""
This is in fact a rather big scattering process !
We 're not talking about high powered lasers here !
I am certainly not "fantasizing" as you say Herald , I think it is just you who wants to be right when you are not .
Nevermind ...

Tbolt :
""
smoke, dust or fog never had any effect on our shooting""
Good to you ;-) It happened to me on different occasions like during Arty splashes , them being HE , ICM or of course Smoke screens .

""
the only problems we ever had was pouring rain and heavy sand storms""
Heavy sand storms are the worse . To start with , it tends to degrade the TIS effectiveness (yes it does) and you can 't lase what you can 't see anyway ! In the 73-Easting battle , US and Iraki Tankers were sometimes shooting at each other from no more than 200-300m ! That 's scary !

""
On the M1 and M1A1 the gunner could chose first return or last return and for me as a gunner and later as a tank commander part of setting up my fire plan was to observe what the terrain and any folage there was between me and the kill zone if i had tall grass shrubs etc i would chose last return knowing that if lazing a tank it would give off the strongest return""
Exactly , terrain recon , choice of a good BP (Battle Position) , small arc of fire to cover only a small area or path , etc , is the sign of a good TC . If someone can hit you from your 3 or 9 O' clock when you 're in a defending position (hull down) , the TC (or the Platoon Commander) made a big mistake . In a good hull down position , the gunner (and the TC) should only see what is in between the 11 and the 2 O ' clock , straight ahead . This way , you only show your best profile : your front turret .

Cheers .



 
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Herald1234    For someone who didn't even understand what i wrote and got what i wrote exactly BACKWARDS   10/24/2007 2:13:18 PM
I wouldn't be claiming anything about anything, BW.
 
Reread and then learn some BASIC EM physics.
 
Herald
 
 
 
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oldcdntanker       10/24/2007 8:03:37 PM
Laser beam divergence is not a cut and dried affair.  I was taught that under standard atmospheric conditions, most tank lasers only have a beam divergence of some 10 - 20 cm per 1000 meters.  However, tankers never work under standard conditions, at least almost never.  Humidity, dust, smoke and even dirty objective lens on the lasing tank all affect the divergence of the beam.  It is conceivable that a tank, with a film of dust on its optics, lasing in high humidity, would have a divergence closer to 40 cm per 1000 meters.  Throw in sand storms, rain, or even snow, and things can get out of hand in a hurry.

Realistically, on the open range, clear laser returns out to 4000 meters are the norm.  Getting a double return is normally the fault of the gunner not laying correctly on the center of visible mass.  On the battlefield, well things do get somewhat different.  What with the smoke and the dust, double returns do happen quite a bit.  Most of the time, the last return is correct, the first return is from the smoke or whatever.

I'm not a technician, mind you....just a retired tanker.

 
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