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RE: Sherman 75mm vs. Tiger side armor test

 
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RE: Sherman 75mm vs. Tiger side armor test - 2/5/2012 10:58:32 PM   
Mobius


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That WO info looks suspiciously like a republication of the US data. British tests may reflect better to find a 75mm Mk V tests. While this has a slightly better muzzle velocity 2050 to the US 2030 it should be more reflective of WO testing.

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RE: Sherman 75mm vs. Tiger side armor test - 2/5/2012 11:54:55 PM   
Yoozername

 

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I am just looking for M72 data as a starting point.  But, yes, the Brits prob had early experience with M72 and also the transition to the M61.  Notably the HE issue.

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RE: Sherman 75mm vs. Tiger side armor test - 2/9/2012 8:41:00 PM   
Mobius


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The M72 had a higher drag factor so it lost velocity faster than the M61. And was nearly a pound lighter than the M61, though that could be counted in the AP cap and the windscreen. So the M72 may had slightly more up close punch but wasn't so good at range.




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RE: Sherman 75mm vs. Tiger side armor test - 2/10/2012 11:46:42 PM   
Yoozername

 

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I am not sure I follow that.  It seems from the data you posted, that the M61 'delivers' 12.5 pounds (see plug w/o cap or windshield) while the M72 is a ~ 14 pound AP shot?  The 'filled' M61 w/M66A1 fuze weighs 14.9 pounds, compared to the M72 13.94.  They supposedly have the same velocity if they share the same optics?  In any case, I agree that the M72 at close range (barring severe quality issues) might have been a better chance against the Tiger sides.  I am starting to suspect that the 'cap' use was making up for poor penetrator manufacturing in the US.

I have been reading lately of the US ammunition woes during WWII.  Not only the HE shell problems with all the sub-contracters but also the AP it seems.  Lots could vary and these problems came up early.  As early as Sicily, there were major problems.  The tests from May 44 of shoots on homog. plate showed very poor showings of the M61 and other US 'cap' antitank rounds.

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RE: Sherman 75mm vs. Tiger side armor test - 2/11/2012 7:12:17 PM   
Mobius


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quote:

ORIGINAL: Yoozername
I am not sure I follow that.  It seems from the data you posted, that the M61 'delivers' 12.5 pounds (see plug w/o cap or windshield) while the M72 is a ~ 14 pound AP shot?  The 'filled' M61 w/M66A1 fuze weighs 14.9 pounds, compared to the M72 13.94.  They supposedly have the same velocity if they share the same optics? 

The velocity bleeds out because of the higher drag factor so besides not having the same velocity at say 1000m it makes it a less accurate round.
Against homogenous armor penetration engineering formulas say all that counts is cross-sectional density. So caps count as weight. (Though we don't rely on penetration engineering formulas in PCO.)

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RE: Sherman 75mm vs. Tiger side armor test - 2/12/2012 2:32:46 AM   
Yoozername

 

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Yes, that's true the M72 was basically a slug with a tracer.  But the 57mm and the 90mm (I believe), had APBC with no cap as designs.  It seems the M3 gun was given the APCBC M61 version as it's armor piercing round for most of the ETO. 

APC (which is actually APCBC) rounds, give up 'vertical' performance against homogenous armor.  They literally have a cap of steel on the front that the penetrator must be pushed through before the penetrator gets to the target armor.  Caps count as weight that must be accelerated down the gun tube.  I believe I read that the M61 had 2# of gunpowder to the M72 1.9#.  They both had the same velocity though.  This due to the M72 lighter weight. 

The M61 seems to be able to not ricochet against sloped homogenous armor compared to face hardened.  But in the case of the Tiger I side armor, the armor is too tough and it has a T/D favorable ratio that seems to negate most M3 75mm hits except those that are dead nuts square-on.




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RE: Sherman 75mm vs. Tiger side armor test - 2/12/2012 3:34:06 AM   
Mobius


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Since the Soviets produced that chart of shell penetrations included the LL 75mm M72 and not the M61 leads me to believe the US sloughed off the M72 on the Soviets. At least until stocks ran out and there was enough M61s for all.

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RE: Sherman 75mm vs. Tiger side armor test - 2/12/2012 4:01:06 AM   
Yoozername

 

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quote:







The M72 info here appears to show it is inferior to M61 against frontal attack against PanzerIII, But look at the note regarding side armor. They mention Valentine homog armor penetrated. Seems it was hard armor too. Is that 1600? 2.5 inch?

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RE: Sherman 75mm vs. Tiger side armor test - 2/12/2012 3:29:18 PM   
Mobius


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quote:

ORIGINAL: Yoozername
The M72 info here appears to show it is inferior to M61 against frontal attack against PanzerIII, But look at the note regarding side armor. They mention Valentine homog armor penetrated. Seems it was hard armor too. Is that 1600? 2.5 inch?

It looks like 1600 yds.
350 BHN isn't far out of the norm for that thick of plates.

quote:

German
BHN
55-80......250-290
35-50......300-350


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RE: Sherman 75mm vs. Tiger side armor test - 2/12/2012 4:50:51 PM   
Yoozername

 

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http://wargaming.info/1998/us-army-1944-firing-test-no1/

The test firing two weeks before D-Day is most interesting.  This site presents it well but it is in several wargaming sites.  I think the M61 test might have the 70mm/60mm Homo 0 and 30 degree data mislabeled.  But firing the M61 against this homo armor shows that the armor effects drop off.  The M61 is not fired against the 100mm or 120mm armor during the tests.  I suppose the TD doctrine said that 75mm shermans had no worries about fighting bigger tanks than Panzer III and possibly Panzer IV.

CONSOLIDATION OF DATA FROM ORDNANCE BOARD PROCEEDINGS 23114 AND 26594
75mm APCBC M61 – HE filled versus Inert loaded

75mm APCBC M61 - HE filled versus Inert loaded

< Message edited by Yoozername -- 2/12/2012 5:00:04 PM >

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RE: Sherman 75mm vs. Tiger side armor test - 2/13/2012 3:03:55 AM   
Yoozername

 

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http://www.youtube.com/watch?v=NKYx1fFhbL0

Nice video of a Tiger being shot-up by an Archer and a Comet (?)

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RE: Sherman 75mm vs. Tiger side armor test - 2/13/2012 8:05:30 PM   
Yoozername

 

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I wonder why this wasn't tried with the sherman M72?

quote:

SHOT, FIXED, A.P.-T., 90mm, T33.
DESCRIPTION. The 90mm Armor Piercing Shot T33 is issued as a fixed complete round for the Gun, 90mm, M3 mounted in Heavy Tank, T26E3 and Gun Motor Carriages, M36 and M36B1. The shot is a modification of the standard AP, M77 which has been reheat-treated and to which a ballistic windshield has been attached.





http://www.lonesentry.com/manuals/90-mm-ammunition/index.html

< Message edited by Yoozername -- 2/13/2012 8:06:01 PM >

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RE: Sherman 75mm vs. Tiger side armor test - 2/13/2012 9:11:40 PM   
Mobius


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The British used the M61 with a plug and inert filler.

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RE: Sherman 75mm vs. Tiger side armor test - 2/14/2012 12:54:41 AM   
Yoozername

 

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I've heard mention of an improved AP round for the 75mm, something like M338 (T148?).  Possibly post-war for use in shermans and M24 tanks.   I believe it was just an improved full bore projectile.

Post-war, the obsoleted 75mm ammunition, which was produced in insane quantities (like 25 million M48 HE), were decommisioned.  The number of tons of recovered powder and metal was crazy.  Production was ramped down in 1944 and someone probably did the math and figured that there was no way it could all be fired.

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RE: Sherman 75mm vs. Tiger side armor test - 2/15/2012 3:45:24 PM   
Yoozername

 

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quote:

Accession Number : ADA954951

Title : Metallurgical Examination of Flame Hardened Gun Shield Manufactured by Continental Foundry & Machine Company.

Descriptive Note : Final rept.,

Corporate Author : WATERTOWN ARSENAL LABS MA

Personal Author(s) : Yoffa,M.

Report Date : 12 FEB 1945

Pagination or Media Count : 10

Abstract : Metallurgical examination was made on a 5 in. thick section of a flame hardened gun shield produced by the Continental Foundry & Machine Co. from Heat No. 6479, Pattern E-6180, Serial 504 and four 3 in. thick flame hardened cast plates manufactured by the same company. All flame hardened pieces had poor metallurgical properties. The fact that a 3 1/2 in. thick section of the flame hardened gun shield had the ability to cause breakage of the 75mm AP M72 projectile may have been due to impacts at appreciable obliquity. (A minimum of breakage was noted when the 3 in. thick flame hardened plate was tested with these projectiles at 0 obliquity.) Under the attack of undermatching uncapped and capped 37mm AP projectiles, 3 in. thick falme hardened cast plate offers greater resistance to penetration than 3 in. thick homogeneous plate. No correlation was made between the poor metallurgical properties of the flame hardened gun shield and the ballistic tests.

Descriptors : BALLISTICS, FLAMES, GUNS, HARDENING, METALLURGY, PENETRATION, PROJECTILES, RESISTANCE, SHIELDING, TEST METHODS, THICKNESS

Subject Categories : METALLURGY AND METALLOGRAPHY
BALLISTICS

Distribution Statement : APPROVED FOR PUBLIC RELEASE




I would like to read the whole report but from this Abstract, I would think the M72 was defetaed by the crappy cast plate due to the flame hardening.

< Message edited by Yoozername -- 2/15/2012 3:48:12 PM >

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RE: Sherman 75mm vs. Tiger side armor test - 2/16/2012 3:03:39 PM   
Mobius


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I don't recall where I found this. Someone made up a chart of 76mm tests vs. plate hardness. I can't verify all the data points but the red and yellow dots seem to assume US test plate is 240-260. But I found them to be 210-230 in one case.





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< Message edited by Mobius -- 2/16/2012 3:04:27 PM >


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Post #: 46
RE: Sherman 75mm vs. Tiger side armor test - 2/16/2012 9:29:29 PM   
Yoozername

 

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Interesting data.  I suppose what jumps out is that the limit velocity, in all cases, is much less than the muzzle velocity.  As far as the 'blue-square' BL(N) M79 AP from BRL Trials vs. 4" RHA, it appears that the limit velocity goes up with target hardness????  I am assuming that all these tests are against RHA of varying hardness.  Note face-hardened.

In any case, as far as the Tiger, I think the Frankford Arsenal Report 1166 is the best stuff I have read.  If you haven't secured a copy of this, let me know.  Basically it is RHA armor attacked at all sorts of angles by 3 types of 20mm penetrators based on the 90mm T33 round.   It goes into shatter-gap and other good stuff.  But in the end, the conclusion is that the 3 types of penetrator shape all have their 'expertise' based on slope, thickness, etc.

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RE: Sherman 75mm vs. Tiger side armor test - 2/17/2012 2:33:12 AM   
Mobius


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I'm going to have to revise my remarks about the BHN of the armor used in tests. Reviewing one Ballistics Data Bulletin it seems different steel BHN was used in tests. The .50 cal penetration charts were based on 350 BHN target while the M61 APC was with 240 BHN steel armor targets. I don't remember where I saw the 210-230 BHN being used. I have to go through my manuals to see if I can find the location.

I did find one report on tests done in 1944 on plates of different hardness levels. 210-350. It did state that plates of 6" could not be made with more hardness of 210 BHN.
This was produced by making scaled down models of the M62 and German 75mm APHE round. Not full sized firing tests.




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< Message edited by Mobius -- 2/17/2012 3:08:13 AM >

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RE: Sherman 75mm vs. Tiger side armor test - 2/17/2012 3:21:44 AM   
Mobius


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I think this is what I had seen. For the 76mm HVAP test.
Probably because they used thicker test plate than that used to test the 75mm.





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RE: Sherman 75mm vs. Tiger side armor test - 7/9/2012 7:14:23 PM   
Mobius


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I just made a little program to compute the exact armor quality equivalency based on the above US Hardness chart. The Germans had a rule of thumb that cast armor (230 BHN) was about 90% the protection of rolled plate armor. If the average German armor hardness is 270-280 i.e. 275 BHN this bears that out. Though there is some evidence that curved and round cast armor is just as strong as rolled armor.




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< Message edited by Mobius -- 7/9/2012 7:15:53 PM >

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