Sherman 75mm Effectiveness

[PzKpfw 1]

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

John,

Why not ask what is the total picture that favors using one or another, which leaves the door open. Refusing to go one way or the other unless unobtainable data is presented shuts all doors and locks them tight.

That is my point.<HR></BLOCKQUOTE>

Lorrin I realy don't know how to ask what I did any difrently. Either way it achieved its purpose to an extant as it got more detailed reply's from you, on your POV on this.

I guess I'm just looking for more emperical answers then you can give to satisfy my own peaked interest in the data you have presented & how common it realy was.

Regards, John Waters

[Blenheim]

Rexford, a question....

Where do you get the time to post so much (and so well) here and writing the book at the same time? Are you still playing to CMBO?

Man, keep posting.

[rexford]

The German tests of 76.2mm Russian guns using 7.6 kg rounds were based on German made APCBC rounds, which were to German nose hardness standards. The rounds had rounded noses.

These are the German made rounds that were fired by the rechambered captured Russian 76.2mm gun on the Marder.

Tests with 7.6 kg projectiles are not indicative of what Russian made 76.2mm APBC flat nose ammunition would penetrate. Those tests do relate what a captured T34 would penetrate using German ammo and a rechambered gun.

The Russian Battlefield and other sources indicate that Russian 76.2mm APBC weighed 6.3 and 6.5 kg.

[rexford]

The true test of equations and theories that are based on a few tank analyses is how well they compare to actual combat results.

Using 85mm for Panther glacis thickness and 65mm for the nose gives better consistency with firing tests against Panther and combat reports than 80mm and 60mm.

85mm is not only 6% thicker than 80mm, it gives a higher slope effect. When 17 pounder hits 85mm and 80mm armor at 55° the armor resistances are 206mm and 221mm at 0°. A 7.2% difference that can make a difference on the battlefield and proving grounds.

We have German and American firing tests against high hardness armor like the T34 carried. The Germans used 37mm and 50mm guns against very hard 45mm plate at various angles, the Americans used 37mm through 90mm ammo.

An equation was prepared and is presented in the book for hits on T34 hardness armor. The predicted penetration ranges for 75L43 against T34 front hull armor compare well with the stories in Jentz.

So a small sample test ends up working well when it is compared to larger scale combat situations. That is the final test and it appears to confirm the general validity of the firing test data and analysis.

That is the best one can do in many WW II research cases.

[ 07-05-2001: Message edited by: rexford ]

[rexford]

Frederic Erk is handling European orders of the book and European orders contact Mr. Frederic Erk at curator@musee-des-blindes.intranets.com

An announcement for USA, Canadian and other orders will be made on the General CM Forum shortly. I will be the contact.

[rexford]

The 76.2mm gun in T34 could penetrate 75mm at 0° and 66mm at 30° at 500m with APBC flat nose ammo. BR-350B ammo.

Note that the 30° slope effect is 75mm/66mm, or 1.14. This is less than the thickness/cosine(angle) and is due to the superior penetration of sloped armor by rounds that dig into the armor.

Instead of ricochet forces on the nose that push upwards and raise slope effects, flat noses tend to turn the projectile into the armor when the noses bite in.

When German 75mm hits 66mm at 30°, the slope effect is 1.23, for Russian APBC it is 1.14.

The differences at 60° are even greater. When German 75mm hits 40mm at 60°, the armor resists like a 106mm vertical plate. Against Russian 76.2mm APBC, 40mm at 60° resists like a 70mm vertical.

Russian flat nose APBC is wonderful against sloped armor and not so good against vertical armor unless the velocity is very high (over 2200 fps or 670 m/s).

[PzKpfw 1]

The data from my post concerned the BR-350 round @ 30^, I did not list the 0^ data Ie, 76mm L/30 @ 500m @ 0^ = 58mm

Regards, John Waters

[ 07-05-2001: Message edited by: PzKpfw 1 ]

[thewood]

After reading the blizzard of posts about the details (some times painful details) of armor penetration and armor thickness, I feel compelled to ask a question; How detailed do people expect CM to be? If you are questioning the as-built to tolerence of armor, should you also consider the same tolerence matching for the ammo? Should you consider the tolerence in propellent charge? Should you also consider the variation in production runs during christmas and Octoberfest?

There are a number of variables in any given situation and a significant amount of forum bandwidth seems to be focused on the under-rating of german armor or the overrating of american armor. When someone states that a certain gun (with Xmm penetration) should penetrate X-1mm or armor and assume that little other than geometry and metalurgy varies the result, I have to wonder if the person is losing sight of the bigger picture that CM represents.

I have worked in the metals and machining industry for years and know the standards by heart. But I also know the processing and the games played with tolerences and can tell you that many measuring systems, including the ruler, are single variable tools with one dimensional answers. I have seen people swear up and down that metals were delivered sub-standard, only to find out the hardness tester was never calibrated or an operator didn't know how to use it, or the user used a sample size of one.

The final measure of any wargame is does the game give close to the results expected using tactics that one would expect to see in combat. I don't think there many people here that can claim to know, and I have to believe that we can find more constructive ways to spend our CM time besides arguing over 5mm of armor.

[PzKpfw 1]

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

After reading the blizzard of posts about the details (some times painful details) of armor penetration and armor thickness, I feel compelled to ask a question; How detailed do people expect CM to be? If you are questioning the as-built to tolerence of armor, should you also consider the same tolerence matching for the ammo? Should you consider the tolerence in propellent charge? Should you also consider the variation in production runs during christmas and Octoberfest?

<HR></BLOCKQUOTE>

If they were painful why read them . As detailed as it can be. I think we have also covered that in te past Ie, ammo, powder nose hardness tolerance, quality etc.

The Xmas & Octoberfest production variation discussion is slotted for next week ...

Regards, John Waters

[thewood]

I'm not saying they are not interesting, but maybe I'm a masochist. Look at the SMG discussion where the discussion continues to go around in circles and spawning itself. After a while people don't read them for information, but to see who is going to say whet to whom. We should probably have a seperate forum for these types of discussions regarding the technical characteristics of the weapon systems, or have the tankersnet set up a discussion in the gamers forum ot that site.

There is ususally some great and useful information in these discussions. Unfortunately it many times gets lost in the clutter. If anyone ignores them and then asks a question that remotely resembles the subject, you are peppered with derisive comments about not reading all of the posts.

Also, many times, even the way people broach the subject is a little off-putting. I sometimes read these forums and think that the guys at BTS must have pretty thick skin. Very rarely do I hear someone say, BTS has done a great job and I know its their decision, but here is what I have found. Instead, someone will come onto the forum and tell BTS that something is wrong and its a great injustice and they have the answer, when in fact they probably only see a small piece of the puzzle and there are other things to consider.

I have a good friend who doesn't come to the forum any more because he has to wade through so many technical discussions that he feels its a waste of time. I personnaly find a lot of interesting, if not entirely useful information. But I continue to find the same people posting over and over again about basically the same subjects. At some point I hope we get to the point that people will just send a suggestion along to BTS and if it starts to get extraordinarily detailed, it moves over to a seperate forum or a more technically oreinted site. This allows people looking for mods, CMBB inforamtion, tactics, or general BTS information to find it easily.

[PzKpfw 1]

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

This allows people looking for mods, CMBB inforamtion, tactics, or general BTS information to find it easily.<HR></BLOCKQUOTE>

Thats why their is a thread subject title, ppl who arn't interested in armor etc, can simply skip threads that don't interest them, no seprate forums needed etc.

As to these threads contiuance on the forum I'd say they still exist because new info is always popping up in them, that eventualy is adressed, & or implemented into CMs engine Ie, the Tiger E mantlet armor was undermodeled, the Jumbo Sherman armor was overmodeled, etc.

Regards, John Waters

[ 07-05-2001: Message edited by: PzKpfw 1 ]

[Nick Carter]

Being a machinist myself, I find these posts very interesting, as ultimately it is the machine tool industry and machinists (ok, engineers too!) who won the war. Successful designs also seemed to have the loosest tolerances, if success is measured by how many of a given unit could be manufactured in a given time (T-34 vs. Panther for instance)

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

I have worked in the metals and machining industry for years and know the standards by heart. But I also know the processing and the games played with tolerences and can tell you that many measuring systems, including the ruler, are single variable tools with one dimensional answers. I have seen people swear up and down that metals were delivered sub-standard, only to find out the hardness tester was never calibrated or an operator didn't know how to use it, or the user used a sample size of one.

<HR></BLOCKQUOTE>

[Dittohead]

Questions?

1. How do they measure the armor thickness in the field? Standards? Does each country do it differently?

2. How many measurements should be taken?

Thanks

Tony

[rexford]

John,

The data you posted for Russian gun penetration appears to use German made ammo for the German tests (7.6 kg weight for projectile), and Russian APBC for Russian tests (6.3 or 6.5 kg projectile).

[PzKpfw 1]

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

John,

The data you posted for Russian gun penetration appears to use German made ammo for the German tests (7.6 kg weight for projectile), and Russian APBC for Russian tests (6.3 or 6.5 kg projectile).<HR></BLOCKQUOTE>

Yes Lorrin thats why I posted what both countries had for results as I thought it was interesting in the difrences in results.

Regards, John Waters

[ 07-05-2001: Message edited by: PzKpfw 1 ]

[rexford]

Regarding the use of DeMarre style analysis, we have U.S. penetration tests for German and Russian ammo against American test plate, and U.S. ammo against the same test plate. Why bother with DeMarre analysis when data is available for a common basis comparison.

There is also the issue of how do nose hardness variations change DeMarre estimate penetration? U.S. penetration tests with 20mm AP at various nose hardness actually underestimate German advantage over U.S. by about 5% when one applies nose hardness factors from 20mm AP tests. Could be 20mm data does not directly scale up to 75mm rounds, or nose hardness is only one factor in a complex picture (impact resistance could be another).

Problems with DeMarre estimates for varying nose shape and nose hardness rounds is why British tested U.S. 76mm APCBC, German 75mm APCBC, 17 pounder APCBC and Russian APBC at 610 m/s against vertical plate.

Russian APBC does not follow DeMarre analysis, because penetration for flat nose projectile does not vary with velocity^1.428 power, it varies by different factors within certain velocity ranges.

We only use DeMarre type equations when there is a need to estimate data for which there is no published figure or a particular figure looks funny (too high or low).

American APCBC does not penetrate as much as German at same velocity, weight and diameter due to nose hardness differences and other factors. British tests at 610 m/s showed this, 103 for German 75mm and 90 for U.S. 76mm. Sherman 75mm APCBC would penetrate 89mm at 610 m/s when DeMarre estimate is made from 76mm penetration in test.

CM has much higher homogeneous penetration for Sherman 75mm APCBC, about 98mm at 610 m/s versus 89mm in British and American tests.

[rexford]

One of the issues regarding published Russian penetration data is the success criteria that was used. Russian tests could use 20% success criteria (20% of hits result in successful penetration), 50% or 80% success.

Germans use 50%, like Americans, most of time. British data generally based on 50% for larger ammo, but some 80% may slip in occasionally.

Using Russian data that does not have the success criteria spelled out is subject to possible variations.

The Russian Battlefield published two types of penetration data, tests at 20% and 80% success criteria and calculations. The calculations ("tabular" data) may not be as reliable as tests, since we don't know the equations used or the assumptions.

Since we have tests for Russian APBC against American plate (50% success criteria), our book presents consistent penetration estimates for all Russian APBC, which we compared to data on The Russian Battlefield. Much of the data on that site is very close to our figures, with notable exceptions.

Americans estimated that 122mm APBC would lose velocity faster with range than Russians did, is one example of a difference.

Russian Battlefield penetration for uncapped AP is lower than our estimates based on nose hardness differences from U.S. AP. About 13% lower, using DeMarre estimate with nose hardness modifier.

Our book presents our estimates for Russian penetration and compares result to Russian Battlefield figures. Book also presents estimates based on British test of 76.2 APBC against vertical plate at 610 m/s, which we compared to our estimate and Russian Battlefield data.

[rexford]

Russian APBC has very low slope effects at high angles, which has been discussed in previous posts. When 76.2 APBC hits 40mm at 60° resistance is same as 70mm vertical plate, when U.S. 76.2mm hits 40mm at 60° resistance is same as 105mm vertical.

The slope effect difference is due to flat nose digging into armor and helping to turn projectile into armor plate, instead of ricochet effect that occurs when pointed or rounded noses strike at an angle.

The potential problem in wargame application of APBC slope effects is that the data is based on softish homogeneous armor (250-300 Brinell Hardness), and most German tank targets for Russian guns will have face-hardened armor where hardness may be over 550 Brinell.

There is no published Russian penetration data for face-hardened armor at 0° and other angles, based on our research (available data is for homogeneous armor, while face-hardened armor has hard thin surface layer and softer body of armor). So Russian penetration data may not address resistance of PzKpfw III, IV and Panther armor due to face-hardening.

And slope effects for Russian APBC against face-hardened armor may be greater than homogeneous tests, since projectile does not dig in as much on face-hardened prior to failure of armor or projectile.

Homogeneous armor defeats hits by allowing round to drive into armor and push plate material around, which uses up energy. Face-hardened armor attempts to break up and shatter projectile before round breaks through hard surface layer.

Face-hardened panzer armor appears to be one of the main issues that face CM2.

[rexford]

Based on U.S. tests of Russian APBC against sloped armor, 76.2mm APBC against T34 glacis (45mm at 60° slope from vertical) would be resisted by 90mm vertical plate equivalence.

If T34 armor is high hardness, modifier would reduce vertical resistance to 68mm at 0°. This suggests that T34 gun firing Russian APBC could penetrate T34 glacis at 875m.

If this is correct, Germans could have ended T34 problem by enlisting captured T34 as T34 tank destroyers.

However, if the slope effects for flat nose APBC are influenced by armor hardness (high hardness or face-hardened), than penetration range for T34 against T34 would be reduced significantly.

There may be a report where T34 gun was fired at T34 to determine resistance, and this would be very valuable to review.

[kipanderson]

Lorrin, hi,

This is all “very” interesting stuff.

Thanks to the research you and your colleague have done I believe a fuller picture is finally starting to emerge as regards the penetration of Soviet rounds.

Charles will clearly have to “tweak” the equations for Soviet ammo, showing less penetration against the vertical but greater penetration at higher angles of attack. i.e. against side armour at 30+ degrees.

In thinking about the “type” of battles there will be in CMBB it is worth remembering that many Panzer attacks will be against “PAK fronts” of twelve or more Soviet AT guns on a map of, say, 1.5km by 2km. In the more open terrain of Eastern Europe there will be any strikes against the side armour of attacking German AFVs. The Soviet advantage at these higher strike angles will show up. I have done a “test shoot” over open terrain using 6 pdrs and attacking Panthers and life is “very” dangerous for the Panthers due to their thin side armour.

All good fun,

All the best,

Kip.

[Jeff Duquette]

The Germans must have been testing Soviet Ordnance against German armor plate at various stages of the War. I am willing to bet that the Germans conducted ballistic tests of Soviet F-32 and F-34 76mm tank guns firing both AP and APBC as part of the design process for the Panther (and perhaps the MkIVF and Tiger I). Probably the Soviet 45mm was test fired against German plate as well. Question number one would be if this test data survived the war. Question number two would be weather the Soviets or the British or Americans got hold of these records right after the war and carted them off to their own respective countries for analysis. This information could be scattered about in the archives of four different countries.

[PzKpfw 1]

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

Lorrin, hi,

I have done a “test shoot” over open terrain using 6 pdrs and attacking Panthers and life is “very” dangerous for the Panthers due to their thin side armour.

All good fun,

All the best,

Kip.<HR></BLOCKQUOTE>

Did you try using PzKpfw IV's on the flanks Kip?.

Regards, John Waters

[gunnergoz]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Nick Carter:

Being a machinist myself, I find these posts very interesting, as ultimately it is the machine tool industry and machinists (ok, engineers too!) who won the war.

--snip--

<HR></BLOCKQUOTE>

Wow, Nick, I had no idea that millions of engineers and machinists were killed in WW2! Who was busy designing and making the armaments that they carried into battle? This totally revises the image I had erroneously built in my mind of WW2! In reality, engineers and machinists fought mano-a-mano in the front line while all those drafted soldiers ran the plants and factories. Wooaaa, dude, I'm shaken to the core!

:eek: