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Cracks found inside Excalibur rounds

dapaterson

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The US Army is doing detailed examination and X-rays of all their Excalibur rounds, after a routine inspection found a minor crack inside the HE material in the warhead.

http://www.defensenews.com/articles/small-cracks-in-excalibur-artillery-rounds-prompt-closer-look-by-the-army
 

Colin Parkinson

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So it's not the casing that is cracked, but the HE inside, I guess to large of a crack and the HE may impact itself and detonate on firing?
 

Pusser

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Colin P said:
So it's not the casing that is cracked, but the HE inside, I guess to large of a crack and the HE may impact itself and detonate on firing?

Correct.  If there is a rapid compression of the gap (i.e. the slamming together of the larger masses of HE material when the gun is fired) the resultant temperature rise (Charles's Law) can be sufficient to ignite any HE dust that could be in between the larger masses.  This in turn could cause the entire mass of HE material to detonate prematurely.  This is actually a known risk with TNT which makes the filling of projectiles with TNT a rather involved process (i.e. TNT is prone to cracking if not poured properly).
 

jeffb

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Especially given that Excalibur is fired high angle, a premature in the bore would be even more catastrophic then low angle. Glad they picked this up before we lost a gun det.
 

Old Sweat

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jeffb said:
Especially given that Excalibur is fired high angle, a premature in the bore would be even more catastrophic then low angle. Glad they picked this up before we lost a gun det.

Ditto to that, and glad that the precision guidance kit that makes a standard HE round "almost as smart" is entering service for a fraction of the cost of an Excalibur round.

Modify to add:

This story from the government information machine reports on 1 RCHA integrating the precision guidance kit with existing equipment and procedures. While the kit apparently does not have the accuracy of the Excalibur, it provides an acceptable alternative at a much lower cost.

Canadian Army 'Hitting the Mark' with New Artillery Capability
November 2, 2016 – Shilo, Manitoba – National Defence / Canadian Armed Forces

Starting this week, the 1st Regiment of the Royal Canadian Horse Artillery will be integrating a new piece of equipment, known as the Precision Guidance Kit, at Canadian Forces Base Shilo, Manitoba.

The integration of the Precision Guidance Kit, which can be used in place of the existing fuse on a conventional shell, transforms artillery rounds into Global Positioning System-guided munitions, allowing trajectory adjustments to be made in-flight, thereby enabling targets to be hit with greater precision.

The Precision Guidance Kit will bring greater accuracy to a normally unguided projectile, and in turn reduce ammunition requirements and the risk of collateral damage. This advanced system is yet another example of the Canadian Army’s commitment to ensuring its soldiers are well-equipped with first-class capabilities.

Quotes
“Developing capabilities like the Precision Guidance Kit will improve the Canadian Army’s ability to more effectively engage a target through the use of artillery. A guided projectile system will reduce the risk of collateral damage, neutralize a small target with fewer rounds, engage targets closer to friendly troops, and increase safety, all while being more cost efficient.”

– Colonel Nicolas Pilon, Director Land Requirements, Canadian Army
Quick Facts
The Precision Guidance Kit is a fuse that affixes to the tip of a conventional high explosive artillery projectile in the same manner as any in-service artillery fuse and controls detonation of the round.
The Precision Guidance Kit uses conventional rounds and the in-service M777C1 howitzer with its advanced digital Fire Control System.
The Precision Guidance Kit initiative was started in Fiscal Year 2010-2011 and is expected to close-out in 2018. The approximate cost is forecast at $28 million. This covers the amount to integrate the Precision Guidance Kit technology to work with the Canadian M777C1 and also covers the cost of purchasing M795 projectiles and Precision Guidance Kit fuses.
The Precision Guidance Kit is manufactured by Orbital ATK in the United States. There are no Canadian companies that currently manufacture this capability.
 

jeffb

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It's interesting that on this extremely high tech munition, the point of failure was the relatively low tech explosive fill.
 

AmmoTech90

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Colin P said:
So it's not the casing that is cracked, but the HE inside, I guess to large of a crack and the HE may impact itself and detonate on firing?

Correct, compression of an HE fill that may result in detonation is called nipping.  105mm Fd Smoke Marker rounds actually use an inert (dye only) bottom piece of fill to prevent this.  It acts like a shock absorber.
 

Journeyman

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jeffb said:
It's interesting that on this extremely high tech munition, the point of failure was the relatively low tech explosive fill.
A catastrophic failure would still be a failure;  kind of like a Space Shuttle O-ring.    :nod:
 

Pusser

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Journeyman said:
A catastrophic failure would still be a failure;  kind of like a Space Shuttle O-ring.    :nod:

This is why attention to detail is important.  Sometimes folks forget that.
 

Petard

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The Excalibur round has an insensitive HE fill, a form of PBX 9, far less risk than TNT to compression/high order detonation; most likely why the comment in the article:
"But because the cracks found in the Excalibur munitions thus far have been small, “there likely would have been no problem,” if they had been fired, Calloway added"
 

AmmoTech90

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Petard said:
The Excalibur round has an insensitive HE fill, a form of PBX 9, far less risk than TNT to compression/high order detonation; most likely why the comment in the article:
"But because the cracks found in the Excalibur munitions thus far have been small, “there likely would have been no problem,” if they had been fired, Calloway added"

Very true, the smoke marker round I referenced has PETN mixed with dye as its fill, pretty much of on the other end of the sensitivity spectrum for secondary explosives.  It would take a very severe shock for Excalibur to nip.
 
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