4.2 inch mortars- different blasts

[109 Gustav]

I just noticed that the American 4.2 inch mortars have a blast of 72, while the British ones have a blast of 47. Why the big difference?

------------------

Well my skiff's a twenty dollar boat, And I hope to God she stays afloat.

But if somehow my skiff goes down, I'll freeze to death before I drown.

And pray my body will be found, Alaska salmon fishing, boys, Alaska salmon fishing.

The Last Defense- Mods, Scenarios, and more!

[Forever Babra]

They must make 'em with Texas chili.

------------------

Stereotypes

[Forever Babra]

Interesting. Just checked that and you're quite right. The American 4.2 inch is about 50% more expensive too, but I thought that was because it had more tubes in a battery.

Explanations?

[John Kettler]

109 Gustav,

The short answer is that the British weapon, because of structural weaknesses in the baseplate, couldn't reach the 4000 yard design range. The solution adopted was a lighter, streamlined bomb which could, but payload was sacrificed to reach it, hence the substantial reduction you're seeing.

Please see Ian Hogg's GRENADES & MORTARS, page 112 for further details, but that's the gist of it.

Hope this helps.

Regards,

John Kettler

[109 Gustav]

Thanks for the explanation. I guess tougher baseplates were out of the question.

------------------

Well my skiff's a twenty dollar boat, And I hope to God she stays afloat.

But if somehow my skiff goes down, I'll freeze to death before I drown.

And pray my body will be found, Alaska salmon fishing, boys, Alaska salmon fishing.

The Last Defense- Mods, Scenarios, and more!

[This message has been edited by 109 Gustav (edited 02-26-2001).]

[Forever Babra]

Originally posted by 109 Gustav:

Thanks for the explanation. I guess tougher baseplates were out of the question.

That IS weird.

EDIT: I just checked the (not terribly reliable) "Complete Encyclopedia of Weapons of WWII". They suggest the problem was not in the baseplate but in the manufacture of the bombs themselves. The bombs were intended to be forged, but the required forging facilities were not available so they had to be cast instead, which impaired their range due to a poorer ballistic shape. The entry did not mention by how much the payload was impaired with the cast bomb, if at all.

I generally trust Hogg on things artillery, but the Encyclopedia explanation sounds more plausible to me.

[This message has been edited by Forever Babra (edited 02-26-2001).]

[Simon Fox]

The bombs were intended to be forged, but the required forging facilities were not available so they had to be cast instead, which impaired their range due to a poorer ballistic shape.

Which raises the question of round effectiveness since there is evidence that cast mortar rounds gave superior fragmentation effect than steel rounds. I am unsure as to how CM determines "blast" but if it is by filling alone then there will be scope for considerable anomaly. Were US 4.2in HE cast or steel?

Though British and US 4.2" mortars are based on the highly successful WWI Stokes mortar I am uncertain as to their subsequent development paths, though I do know that the US mortar was substantially redesigned. Of course a WP/smoke round was freely available for both in WWII hehe.

------------------

"Stand to your glasses steady,

This world is a world of lies,

Here's a toast to the dead already,

And here's to the next man to die."

-hymn of the "Double Reds"

[Forever Babra]

Well, I don't have Hogg's Mortars book, and, ike I say, the source I referred to is not terribly reliable most of the time. But what I know about metallurgy would fit on a pin-head. Maybe John can throw us a bit more info.

------------------

Mein Vater, mein Vater, und hörest du nicht,

Was Erlenkönig mir leise verspricht? -

Sei ruhig, bleibe ruhig, mein Kind;

In dürren Blättern säuselt der Wind.

Stereotypes

The Un-Rant

[Guest Mike the bike]

My knowledge of metal forming techniques fits on 2 or 3 pin heads, but here's what I recall -

Forging produces better surface finish, better/more uniform grain structure and can be done to closer tolerances than casting.

This means better aerodynamics and more consistant fragmentatino for the forged round vs teh cast one.

I also recall that the Brit 3" mortar suffered similar problems??

[Simon Fox]

I have had a bit of a hunt around and it seems the US and British 4.2in mortars are totally different weapons which bear little resemblance to one another apart from the calibre. The British 4.2in is a conventional type mortar with fin stabilised rounds. In contrast the US weapon is a rifled weapon in which the rounds are stabilised in flight by spin. It's rounds are substantially larger and different than the British weapon, so hence the different blast rating. It is quite different to the more recent US 4.2in mortars since they underwent redesign following WWII.

As for the issue of cast vs steel. It may be that steel casings are stronger and allow more charges and therefore increased range (I don't know). But cast casings were definitely found by the British to be superior for fragmentation effect.

In WO 291/129 "Lethality of 3" mortar HE bomb" The cast iron (Mark IV) bomb was found to be clearly superior to the the steel (Mark III) bomb because of finer fragmentation. In fact it was almost twice as good with a substantially larger vulnerable area. Which just goes to show that weight of HE isn't everything.

------------------

"Stand to your glasses steady,

This world is a world of lies,

Here's a toast to the dead already,

And here's to the next man to die."

-hymn of the "Double Reds"