SHERMAN 75MM PENETRATION

[rexford]

Figures presented in CM for 75mm Sherman penetration appear to be solid AP shot, which may not have been primary anti-tank round during 1944 and 1945. TM-9-1907 lists APCBC-HE penetration as 91mm at 0m and 82mm at 500m.

We've seen pictures of 75mm AP in France but solid shot seems to be in the minority. 75mm solid AP shattered alot in North Africa, and U.S. converted AP rounds to something else (APCBC-HE) to save material that would otherwise have been lost.

Was 75mm AP a training round by France?

[Bastables]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Figures presented in CM for 75mm Sherman penetration appear to be solid AP shot, which may not have been primary anti-tank round during 1944 and 1945. TM-9-1907 lists APCBC-HE penetration as 91mm at 0m and 82mm at 500m.

We've seen pictures of 75mm AP in France but solid shot seems to be in the minority. 75mm solid AP shattered alot in North Africa, and U.S. converted AP rounds to something else (APCBC-HE) to save material that would otherwise have been lost.

Was 75mm AP a training round by France? <HR></BLOCKQUOTE>

Remember that the British prefered solid shot to APHE shells to the extent that they actully removed the HE and inserted a solid in USA APHE shells for use with their 7,5cm guns. 7,5cm AP rounds made by the British were always solid shot.

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Absolutely Shatter, you have been completely misunderstood. When Andreas, Chuppy and Peter posted pictures of themselves at the IWM I took the earliest opportunity to complement Chuppy on how hot he looked in that T-shirt. Of course the next time an appropriate thread about the front bogey wheel on the Matilda II came up I skillfully insinuated a subtle remark about what a spunk PeterNZ was and a redhead too!

But alas, shatter, everyone thought I was a dickhead as well.

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Muddying the waters as usual.

by Simon Fox

Mr T says "I pity the foo!"

[Bastables]

I think Rex may have tumbled on to something here. The 7,5cm gun used in the Cromwell and the Churchill were not identical to the 7,5cm guns supplied by the USA: M3 7,5cm/L40 and the M6 7,5cm/L39. The Cromwell and Churchill on the other hand mounted the locally manufactured Ordnance, QF, 7,5cm/L36.5 MK.V and MK.VA, which is just a rebored 6pdr. Now this is a different gun with different velocity firing the same USA M61 7,5cm cartridge (Although it had the HE charge removed in Commonwealth service); 619m/s M3/M6 vs. 618 for the QF MK.V/MK.VA. Yet inspite of the British and the USA utilizing different ‘ammo’ relative to each other and the Cromwell and the Churchill utilizing a different gun entirely, all Allied AP within CM, performs in a identical fashion. (going by the black info/stats box in game.) Is this correct?

(Chamberlain, Peter and Ellis, Chris British And American Tanks Of World War II)

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Absolutely Shatter, you have been completely misunderstood. When Andreas, Chuppy and Peter posted pictures of themselves at the IWM I took the earliest opportunity to complement Chuppy on how hot he looked in that T-shirt. Of course the next time an appropriate thread about the front bogey wheel on the Matilda II came up I skillfully insinuated a subtle remark about what a spunk PeterNZ was and a redhead too!

But alas, shatter, everyone thought I was a dickhead as well.

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

Muddying the waters as usual.

by Simon Fox

Mr T says "I pity the foo!"

[This message has been edited by Bastables (edited 01-06-2001).]

[rexford]

Rounds with caps will have less penetration at close range than uncapped AP, because caps absorb energy as they collapse.

Does American ammo penetration for Sherman 75mm vary from British?

[Bastables]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Rounds with caps will have less penetration at close range than uncapped AP, because caps absorb energy as they collapse.

Does American ammo penetration for Sherman 75mm vary from British?<HR></BLOCKQUOTE>

Not in CM, although I'm sure it should vary, they're different guns firing different ammo; Brit/Shot USA/Shell, but for some reason all Allied 7,5cm guns have identical stats.

[This message has been edited by Bastables (edited 01-07-2001).]

[Simon Fox]

Bas,

I agree they would be different. But, the difference is probably so small as to be not worth incorporating. I would be interested if the two gun systems had different accuracies though.

Rexford,

What's 'close range'? And as Bas points out the APCBC was used exclusively AFAIK except no HE in the British round (I beleive the US eventually saw sense on this too).

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Muddying the waters as usual.

[rexford]

Filling the HE burster in 75 APCBC adds about 10% to the penetration. U.S. data for HE burster 75mm shows 91mm at 0m, 82mm at 500m.

A 10% increase can be alot.

Does CM have 50% penetration when penetration exactly equals armor resistance?

If CM does use the navy ballistic limit for penetration, than a 10% increase in penetration raises a 50% probability penetration (pen.=armor resistance) to almost 100% success.

The difference between 82mm and 89mm can make a difference on Tiger and Panther side hits at an angle, inside 500m range.

[Simon Fox]

Care to elaborate on the rationale behind the 10% difference?

and bumpity bump

[rexford]

Hunnicutt says Brits took out HE burster and put an "inert filler" in the round, could be sand with same weight as HE. Hunnicutt says resulting projectile had same ballistics as original, suggesting it wasn't filled with metal cause that would increase the weight, lower the muzzle velocity an change the flight path so the gun sight wouldn't match the projectile any more.

APCBC with an HE burster loses penetration because the HE burster opening weakens the projectile structure so that it absorbs impact energy during hits, which lowers penetration compared to solid shot.

If we assume that Brits used sand filler to maintain same exact weight, then 75mmL40 APCBC penetrates the same whether Brit or U.S. and we continue to ask why CM for 75mm APCBC is about +10% above U.S. penetration data when 76mm APCBC is about -8% below U.S. data. Both rounds were similar in size and construction.

Based on our analysis of German data in another message, the physics model appears to lower penetration as velocity increases and the model may give bonus' to low velocities.

One reason Brits were afraid of HE bursters is cause spaced armor on PzKfpw III caused round to detonate inbetween spaced armor and main plate, defeating round.

[Bastables]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Hunnicutt says Brits took out HE burster and put an "inert filler" in the round, could be sand with same weight as HE. Hunnicutt says resulting projectile had same ballistics as original, suggesting it wasn't filled with metal cause that would increase the weight, lower the muzzle velocity an change the flight path so the gun sight wouldn't match the projectile any more.

APCBC with an HE burster loses penetration because the HE burster opening weakens the projectile structure so that it absorbs impact energy during hits, which lowers penetration compared to solid shot.

If we assume that Brits used sand filler to maintain same exact weight, then 75mmL40 APCBC penetrates the same whether Brit or U.S. and we continue to ask why CM for 75mm APCBC is about +10% above U.S. penetration data when 76mm APCBC is about -8% below U.S. data. Both rounds were similar in size and construction.

Based on our analysis of German data in another message, the physics model appears to lower penetration as velocity increases and the model may give bonus' to low velocities.

One reason Brits were afraid of HE bursters is cause spaced armor on PzKfpw III caused round to detonate inbetween spaced armor and main plate, defeating round.<HR></BLOCKQUOTE>

CM attempts to model the brittle US shells, at the lower velocities brittleness is irrelevant and only plays a part at the higher velocities.

[Guest Big Time Software]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford: Filling the HE burster in 75 APCBC adds about 10% to the penetration<HR></BLOCKQUOTE>

Please let me know your source for that figure.

<BLOCKQUOTE>quote:</font><HR>Does CM have 50% penetration when penetration exactly equals armor resistance?<HR></BLOCKQUOTE>

Yes.

Charles

[rexford]

U.S. rounds shatter failed due to nose hardness, not brittle ammo. Rockwell C hardness of 56 leaves round vulnerable to shatter gap.

U.S. 75mm APCBC should have lower penetration than U.S. test data if service rounds were brittle, data in CM is about 10% higher than U.S. tests.

If Americans used more Shermans than British, shouldn't American penetration be depicted?

[rexford]

It would be interesting to see the reference for "brittle" U.S. field ammo. Discussions with Robert Livingston did not mention this issue, and he uses penetration data from U.S. firing tests without any modification for brittleness.

As noted in previous message, U.S. rounds shattered due to nose hardness being low, which permitted cracking under overpenetration.

[Guest Big Time Software]

The brittleness issue does not affect the 75mm round as its striking velocity is not high enough to uncover the flaw.

Is is an issue for the U.S. 76mm APCBC round, however.

Charles

[Simon Fox]

I'm a little confused here as you (rexford) appear to contradict yourself.

First you say: <BLOCKQUOTE>quote:</font><HR>Filling the HE burster in 75 APCBC adds about 10% to the penetration.<HR></BLOCKQUOTE>Your rationale for this seems reasonable to me: <BLOCKQUOTE>quote:</font><HR>APCBC with an HE burster loses penetration because the HE burster opening weakens the projectile structure so that it absorbs impact energy during hits, which lowers penetration compared to solid shot.<HR></BLOCKQUOTE>Yet you now say: <BLOCKQUOTE>quote:</font><HR>If we assume that Brits used sand filler to maintain same exact weight, then 75mmL40 APCBC penetrates the same whether Brit or U.S.<HR></BLOCKQUOTE>Can I take it that you initial assumption was based on a metal filler and your latest upon sand?

Finally while the spaced PzIII armour was a factor in preference for solid APCBC by the Brits my understanding is that the principal ratinale was that the internal damage to the vehicle as a result of penetration was more than adequate for projectiles over 50mm.

[rexford]

Filling the HE burster with metal will increase penetration at a given velocity.

However, heavier rounds will come out of the barrel slower, which decreases penetration somewhat.

If sand is used as a filler instead of HE burster, round penetrates same as with burster and has same velocity-rnage profile.

[Bastables]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Filling the HE burster with metal will increase penetration at a given velocity.

However, heavier rounds will come out of the barrel slower, which decreases penetration somewhat.

If sand is used as a filler instead of HE burster, round penetrates same as with burster and has same velocity-rnage profile.<HR></BLOCKQUOTE>

My understanding is that the HE buster charge actually decreases the number of full 100% perforations, but the point of having a HE charge is to insure lethal affects upon the crew without having to achieve a full 100% perforation. There is a story in Michael Reynolds Steel Inferno of a SS PIV crew note ting that that a British 7,5cm/17pdr shot passing through both sides of their PIV and having to have the turret replaced. I think that what you’re trying to state is that there is a higher chance of a knock out. Also the figures given here show that the British modified M61 7,5cm ammo fired at 618m/sec (out of a shorter gun mind you) had a small 2mm penetration advantage at 457m over the USA unmodified M61 7,5cm ammo which left the gun at 619m/s. British: http://www.wargamer.org/GvA/weapons/british_guns5.html

USA http://www.wargamer.org/GvA/weapons/usa_guns5.html

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Absolutely Shatter, you have been completely misunderstood. When Andreas, Chuppy and Peter posted pictures of themselves at the IWM I took the earliest opportunity to complement Chuppy on how hot he looked in that T-shirt. Of course the next time an appropriate thread about the front bogey wheel on the Matilda II came up I skillfully insinuated a subtle remark about what a spunk PeterNZ was and a redhead too!

But alas, shatter, everyone thought I was a dickhead as well.

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

Muddying the waters as usual.

by Simon Fox

Mr T says "I pity the foo!"

[This message has been edited by Bastables (edited 01-09-2001).]

[This message has been edited by Bastables (edited 01-10-2001).]

[rexford]

Bastables' post suggests that British and American penetration for 75mm APCBC from Sherman was essentially the same regardless of what was in the HE burster cavity. Shouldn't the U.S. test data for Sherman 75 be used, which results in about a 9% reduction in penetration (91mm at 0m, 82mm at 500m).

[rexford]

Based on the web sites provided by Bastables, British APCBC for 75mm weighed less than U.S. 75mm APCBC, 14.96# for American and 14.43# for British, with British round penetrating 2mm more at 500 yards and 30°.

The penetration difference amounts to about 2.5mm difference at 0° and 500 yards.

The following conclusions might be drawn:

1. British 75mm APCBC HE burster cavity does not appear to have been filled with metal or it would have weighed more than U.S. round, not less.

2. Lower weight of British ammo suggests a sand filler, which is inert and meets Hunnicutt's explanation. Sand may also have a lower density than TNT, which might account for the reduced weight of British APCBC.

3. Neither British or American 75 APCBC appears to penetrate 89mm at 0° and 500m, as listed in CM, and neither could penetrate 97mm at 100m based on published data.

The bottom line is that 89mm penetration at 500m, and 97mm at 100m, appears too high for American and British Sherman 75mm. 82mm at 500m for U.S. and 85mm for British appears closer to actual.

U.S. 75 would penetrate 90mm at 100m, British 93mm.

Granted these are small changes but CM data exceeds American and British test data, and battle rounds usually penetrate less than lab tests, not more.

[Bastables]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Based on the web sites provided by Bastables, British APCBC for 75mm weighed less than U.S. 75mm APCBC, 14.96# for American and 14.43# for British, with British round penetrating 2mm more at 500 yards and 30°.

The penetration difference amounts to about 2.5mm difference at 0° and 500 yards.

The following conclusions might be drawn:

1. British 75mm APCBC HE burster cavity does not appear to have been filled with metal or it would have weighed more than U.S. round, not less.

2. Lower weight of British ammo suggests a sand filler, which is inert and meets Hunnicutt's explanation. Sand may also have a lower density than TNT, which might account for the reduced weight of British APCBC.

3. Neither British or American 75 APCBC appears to penetrate 89mm at 0° and 500m, as listed in CM, and neither could penetrate 97mm at 100m based on published data.

The bottom line is that 89mm penetration at 500m, and 97mm at 100m, appears too high for American and British Sherman 75mm. 82mm at 500m for U.S. and 85mm for British appears closer to actual.

U.S. 75 would penetrate 90mm at 100m, British 93mm.

Granted these are small changes but CM data exceeds American and British test data, and battle rounds usually penetrate less than lab tests, not more. <HR></BLOCKQUOTE>

I love you Rex. Although with the modified British shot being lighter would it not lose velocity slighty faster vs the American shell?

[This message has been edited by Bastables (edited 01-11-2001).]

[rexford]

And Sherman 75mm rounds would be subject to shatter gap failure when penetration exceeds armor resistance by 5% to 25%, since shatter gap is based on softness of projectile nose and is not related to any brittleness that may be present.