# A Question about HEAT



## LordOsborne (7 Aug 2007)

I have a question regarding the nature of HEAT warheads. I came across the following paragraph on Wikipedia, which was explaining how HEAT worked and so forth:



> HEAT rounds are less effective if they are spinning, the normal method for giving a shell accuracy. The centrifugal force disperses the jet, so the warhead design needs to be modified for use with rifled guns, or fired from smoothbore weapons


http://en.wikipedia.org/wiki/High_Explosive_Anti-Tank

This got me to thinking: If rifling, which imparts spin to the projectile, decreases the effectiveness of HEAT rounds, then how does the Carl Gustav's HEAT round compensate? I know the projectile (FFV-551?) has flick-out fins once it leaves the tube, but I thought these were for stability in flight. Do they counteract the spin as well? Also, I understand that the Leopard C2's 105mm L7 rifled gun fires HEAT shells. Are these somehow compensated for spin as well, or is the article inaccurate? 

I found this Army News video of an ERYX launch on the range, and it seemed to me (I could just be seeing it incorrectly) that the missile was spinning quite noticeably on its way to the target. Yet, despite the spin that i see, the missile is rated to be capable of defeating 900mm of RHA. 
http://www.army.forces.gc.ca/lf/English/6_1_1_1.asp?id=780

Can someone clarify for me whether or not spinning reduces the effectiveness of HEAT rounds? and, if so, why are some HEAT rounds able to spin and still function?


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## AmmoTech90 (7 Aug 2007)

Yes, spinning does have a detrimental effect on the penetration of a HEAT projectile.  I'll cover Eryx first, it doesn't spin fast enough to have a major effect on the warhead, you are talking a very low rpm (>100 to low hundreds) when compared to the 1000s-10000s rpm that a cannon/gun projectile will experience.  So you can just spin stabilization in most missiles with HEAT warheads.  For example the M72A5 spins at 10 rps.
The FFV551 has a nylon slipping ring on the projectile that takes up the spin.  Low friction between the shell body and the slipping ring, the slipping ring spins a lot, the shell spins a bit.
There is no HEAT round for the L7 (well the French made one but it is hugely complex with a two part shell body which had an outer body with a ball bearing race surrounding an inner body which had the warhead...to complex).  We have HESH for the L7 which does need spin for normal stability.  Don't think anyone has made a fin stabilized HESH round.  That is one of main complaints the Brits have against going to a smooth bore gun for Chally 2, no HESH.


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## Franko (7 Aug 2007)

As AmmoTech 90 said.....panzers don't use HEAT, only Sabot and HESH.

The new panzers though can...           >

Regards


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## George Wallace (7 Aug 2007)

Recce By Death said:
			
		

> As AmmoTech 90 said.....panzers don't use HEAT, only Sabot and HESH.
> 
> The new panzers though can...           >
> 
> Regards



And that is because they are not "rifled" but "smooth bore".


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## Franko (7 Aug 2007)

George Wallace said:
			
		

> And that is because they are not "rifled" but "smooth bore".



120mm of sexy smooth bore death dispenser.....           ;D


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## vonGarvin (7 Aug 2007)

With regards to HESH, without getting all technical, it REQUIRES a spinning effect in order to function in its desired manner.  That is all.


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## LordOsborne (7 Aug 2007)

Very interesting... I appreciate the prompt replies and the wealth of information. I had read that ball bearing rounds existed for rifled guns, but I didn't know the Leos don't use HEAT. 

Another question about the Eryx: I was given a famil class on the system this summer (got to handle the tripod, launcher, Mirabel sight and a dummy missile round) and one of the course officers was telling the course that the Eryx had a fairly unreliable performance, especially at longer ranges. I read that it can have as high as 95% hit rates, but i'm sure that depends on gunner skill and other factors. Can anyone shed some light on this?

I found this to be a good read on the missile:
http://www.armyrecognition.com/forum/viewtopic.php?t=444


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## mudrecceman (8 Aug 2007)

George Wallace said:
			
		

> And that is because they are not "rifled" but "smooth bore".



Who went with the 120 SB first...the Brits, the Germans or the Yanks?  IIRC they all use the same basic tube (Rheinmettal).

Just curious...


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## HItorMiss (8 Aug 2007)

I know it was not the Yanks as the M1A1 sported a 105mm Main Gun which they switched to the 120mm Main Gun shared in common with the Leo2. In fact I would Hazard a guess that it was the Germans that went with the current 120mm Main Gun and the other Big 2 Tank producers decided to switch to it. That is pure speculation on my part however I do know for certain that as I stated the 120mm Main on the Abrams is the exact same as the 120mm Main in the Leo2 and the Yanks moved to that after first having a 105mm on it's top MBT.

So really that leaves Germany and England, now look at the first date of production on the Leo and the Challenger an you'll come up with who used it first.


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## vonGarvin (8 Aug 2007)

Good guess, HoM.  UK uses 120 rifled, Leo 2 started with 120 smooth. M1 used 105mm, M1A1 uses 120 smooth.


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## George Wallace (8 Aug 2007)

Actually, guys, we have to be careful here.  Yes they are 120mm barrels, but we also have two types of Rhinemettal barrel.  L-44 and L-55, both smooth bore, with L-55 being longer.  Not all 'marks'/models have the same gun, so we are going to have different ballistic characteristics with each.


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## dapaterson (8 Aug 2007)

And, just a reminder, certain characteristics of weapons systems are not for the public domain.  So be careful what you post.

Or, in the words of a WWII poster, "Be like Dad.  Keep Mum."


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## DG-41 (8 Aug 2007)

If you want weapons characteristics, go read tanknet.

Once you trim out the Gavin stuff, there's a ton of incredible info there.

DG


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## MJP (8 Aug 2007)

PatrickO said:
			
		

> Another question about the Eryx: I was given a famil class on the system this summer (got to handle the tripod, launcher, Mirabel sight and a dummy missile round) and one of the course officers was telling the course that the Eryx had a fairly unreliable performance, especially at longer ranges. I read that it can have as high as 95% hit rates, but i'm sure that depends on gunner skill and other factors. Can anyone shed some light on this?
> 
> I found this to be a good read on the missile:
> http://www.armyrecognition.com/forum/viewtopic.php?t=444



total thread hijack

I've seen the Eryx fired quite a bit at both longer and shorter rangers and if anything the missle seeems to have a better chance of hitting the further out the target is.  By then during the flight the gunner has calmed down after the missle has left the tube (which btw the missle goes up and to the right to prevent grounding) and is better able gently guide the missle onto the target.  I know we have had some very unreliable performance from the missles, the video from UTube is just one of a few examples, I have a video from my DP3A that shows the flight motor not kicking in and the missle grounded itself 20 meters from the firing line.

As not to continue the hijack if you want more info just drop me a PM.


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## mudrecceman (8 Aug 2007)

HitorMiss said:
			
		

> I know it was not the Yanks as the M1A1 sported a 105mm Main Gun which they switched to the 120mm Main Gun shared in common with the Leo2.



Umm, actually the M1 used a 105, the M1A1 went to the 120 SB, and the M1A2 added the CITV.   ;D

Capt Sensible, good point on the Challenger.  My bad!

I really was just curious as to who used a 120 SB first..but you are likely right HoM...sounds like the Germans did it first...


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## AmmoTech90 (8 Aug 2007)

Don't forget that the barrel size doesn't determine the ammo that is fired.  The barrel length improves performance generally, but as long as the chamber size stays the same you can continue to fire the same ammo.  For example the Italians have a 47 calibre barrel, the French a 52, and the Rhinemetall guns have 44 or 55 calibre lengths.  They can all fire "NATO standard" 120mm tank ammo.


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## Lance Wiebe (8 Aug 2007)

Going back to the original post, both APFSDS and HEAT have degraded performance with spin.  The Germans and Americans both fired HEAT from the L7 rifled 105, they cured the spin problem the same way as they cured it with the APFSDS round, they used nylon slip rings.  The nylon rings would bite in to the rifling, but would impart very little spin to the projectile.  Using the nylon slip rings actually meant that the HEAT projectile was actually less than 105mm in diameter....just a bit of trivia.


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