75mm HE Effectiveness on John Salt Site

[rexford]

Salt5 has some very good British analyses of relative HE effectiveness, see WO 291/955.

U.S. 75mm HE is shown to be more effective than 76mm HE on the basis of total shell weight and HE filler. CM missed this, it would seem, if British stats are correct.

75mm M48 weighs 14.6 lbs and has 1.7 lbs of explosive, 76mm M42A1 weighs 12.9 lbs with 0.9 lbs HE. 76mm puts out less scrapnel at lower speeds, so is less lethal than 75mm HE.

Following is conversion of various HE shells to equivalent 25 pdr HE weight:

75mm 25 lbs

76mm 20

90mm 30

105mm 40

6 pdr 10

17 pdr 20

25 pdr 25

95mm 35

3.7" how 25

This data is slightly different than U.S. figures from TM-9-1907 but looks authoritative and gives HE shell weight and HE filler lbs for a large number of rounds. Nice looking info.

Another bit of info on same site gives 2900 square feet for 75mm HE imnpact area, 2200 square feet for 76mm.

[rexford]

Same site states that 75mm M48 HE is longer, heavier and has greater capacity than 76mm M42A1 HE.

This supports earlier thread I started some time ago using TM-9-1907. And it shows that 75mm HE outclassed 76mm HE in every way, including total scrapnel weight.

Those John Salt snippets are very good.

[jasoncawley@ameritech.net]

That is interesting, yes. But it is not as much of a difference as the headline figure may make it seem. Using a circle to approximate the ellipse of shrapnel, those two areas correspond to "everything within 10 yards" vs. "everything within 9 yards". Hardly an earth shattering difference. Or in meters, 9.35m vs. 8.15m - about.

Certainly enough of a difference to justify some difference in blast rating. But CM's fineness for the placement of units is only 2 meters, and I believe the multi-man counters occupy 2-3 of those "pixels" in each dimension, for combat purposes. Where the squad actual is, and the placement of the men within it, would be as big or bigger a factor, than which type landed 6-10 meters away.

Just to keep some perspective on how fine-grained differentiation of weapons can really afford to get, and still work in practice with the CM engine.

[Vanir]

Originally posted by rexford:

U.S. 75mm HE is shown to be more effective than 76mm HE on the basis of total shell weight and HE filler. CM missed this, it would seem, if British stats are correct.

?

CM gives 76mm a blast rating of 33, 75mm blast rating of 39. Or were you suggesting the difference should be greater?

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What a bunch of horsecrap. -Steve

[Simon Fox]

That's right rexford 75mm HE should be better than 76mm HE. BTS please fix or somefink!

Err Ooops!

Snork

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"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"

[Jeff Duquette]

Rex: We did kind of start touching on this over on tanknet. A discussion on the 17-pdr. HE effectiveness. Anyway here are the CM numbers of interest

Combat Mission Data

75mm M48HE Blast = 39

76mm and 3” M42A1 Blast = 33

105mm Blast = 77

So there are some subtle differences accounted for at least in the M48HE and M42A1 data. Looking at TM9-1907 (23 Sept 1944) one has to wonder if lethal area is an overly simplified way of looking at the problem. Page 233 of TM9-1907 details Shell fragmentation for both M48HE and M42A1HE…excerpts:

Initial Fragment Velocity: 75mm M48HE = 3,120 fps

Initial Fragment Velocity: 76mm M42A1HE = 2,260 fps

Total number of effective fragments @ range from burst

Range from Burst__________20ft______40ft____100ft

75mm M48HE_________________1,070______750_______450

76mm/3”M42A1HE______________547_______465_______331

Fragmentation density of the M48 is actually close to that of the 105mm M1 round, although the 75mm peters out faster in frag density with range relative to the 105mm.

Of additional interest, and somewhat indirectly related to the 75mm and 76mm potential HE lethality is the dispersion of both these rounds. 75mm is a relatively low muzzle velocity weapon. 76mm is a relatively high muzzle velocity weapon. Infact the muzzle velocity of the 76mm’s 42A1HE round actually exceeds that of the 76mm’s APCBC round. The horizontal dispersion zone of the 75mm is therefore considerably smaller than that of the 76mm.

[This message has been edited by Jeff Duquette (edited 03-12-2001).]

[rexford]

The interesting thing about the John Salt HE data is that it supports the CM HE ratings, with 90mm and 105mm HE given a larger 25 pdr HE equivalency than 75mm HE. Although 90mm HE does not appear to be appreciably larger than 75mm HE.

U.S. data in TM-9-1907 suggested that 75mm HE effectiveness was closer to 105mm and 90mm HE, which may not be reasonable. So the John Salt data helps to put TM-9-1907 in perspective.

My comment about CM missing 75mm superiority over 76mm HE was an error.

The British estimates for effective blast area were based on total weight of HE round that hit ground, so may not have considered weight of HE filler which would increase 75mm HE advantage.

[rexford]

The one point about the British analysis of HE equivalency to 25 pdr HE is that it seems to be based on amount of metal and HE filler.

If one looks at the percentage of total shell weight that is HE filler, and considers shell wall thickness (thinner at lower velocities) then it is possible that 75mm HE was comparable to 90mm HE, slightly less effective than 105mm HE close to the blast and alot more effective than 76mm HE than most rulesets predict.

In other words, the U.S. fragment analysis in TM-9-1907 may be justified on the basis of factors that were not considered by the British.

[rexford]

With regard to the preceding post, 75mm M48 HE shell is about 11.5% HE filler, same as 90mm HE. But 90mm HE may have relatively thicker walls, so more resistance to explosion, leading to fewer and larger fragments with less velocity.

The above explanation would be consistent with TM data that predicts more 75mm pieces with high velocity at close range. The larger size of 90mm fragments would hold velocity better than 75mm, resulting in smaller differences between the two (effective fragments) as range increases. This is what happens with TM data.

The above explanation seems to explain the TM-9-1907 data and brings up some issues that may not be considered in the John Salt data.

Input would be appreciated.

Thanks.