88L71 PENETRATION

[rexford]

88L71 APCBC penetration has been subject of

much past discussion and here is another angle.

DeMarre equation allows penetration to be estimated from a reference, and works very well if ammo quality is consistent (also allows 57mm ACPCBC penetration to be estimated very well from 90mm APCBC< or vice versa).

For 88L71 APCBC we'll treat U.S. 75mm APCBC as DeMarre reference, with 91mm penetration at 2030 fps for 75mm M61 U.S.:

88L71 pen = 91 x (velocity/2030)1.428 power

x (88/75)1.07143 power

x ((10.16kg x 2.2lbs/88 cubed)/(15 lbs/75 cubed))raised to 0.7143 power.

Here is 88L71 velocity vs. range data from German booklet on ammunition:

0m-3247 fps

500m-3123

1000m-2972

1500m-2821

2000m-2673

2500m-2532

3000m-2391

3500m-2257

4000m-2125

Plugging velocity into DeMarre equation yields following 0° penetration if 88L71 APCBC ammo were same quality as U.S. 75mm:

0m-199mm

500m-189mm

1000m-176mm

1500m-163mm

2000m-151mm

2500m-140mm

3000m-129mm

3500m-119mm

4000m-109mm

We have seen British data where 30° test penetration of Panther and Tiger guns is much higher than German data, which British attribute to harder German test plate (harder to penetrate?). Americans fired German 75L46 APCBC at same velocity as U.S. 75mm at U.S. plate and "German penetration was somewhat higher".

If British reports during WW II of Panther 30° are converted to 0° using T/D multipliers the result is 190mm penetration for Panther at 0m and 0°. Since Germans list Panther penetration as about 168mm at 0m/0° (estimated from 30° test penetration using assumed slope effect), this suggests that German test plate was "harder to penetrate" and German rounds outpenetrated U.S. due to greater nose hardness (60.7 average Rockwell C hardness on German rounds analyzed by Brits as opposed to 56 Rockwell C hardness for U.S. ammo).

If we do a DeMarre for Panther 75mm at 3068 fps from U.S. 75mm we obtain 164mm at 0m/0°, suggesting German ammo outpenetrates U.S. by 190/164, or 1.158 ratio.

Multiplying previous DeMarre estimates for 88L71 by assumed German quality advantage (1.158)leads to:

0m-230

500m-219

1000m-204

1500m-189

2000m-175

2500m-162

3000m-149

3500m-138

4000m-126

This would be the penetration against U.S. best quality test plate with 240 Brinell Hardness Number, corresponds to good U.S. armor without flaws after October 1943 when quality control and quenching practices improved.

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

There is another way to look at German penetration data based on 30° slope multipliers. British BIOS report data on German penetration lists 30° figures, so where did Germans get those 0° figures? They probably calculated them using assumed figures:

Look at the slope effects for 88L71 that result from published data:

100m (202@0°)/(177@30°)=1.14 slope effect

2000m (132@0°)/(121@30°)=1.09 slope effect

We have studied slope effects for U.S. APCBC and above figures look bogus. If U.S. 90mm APCBC hits a 180mm thick plate at 30°, the slope effect is about 1.32. Why would 88L71 be 1.14?

Lets convert German 30° penetration figures to 0° using U.S. slope effects:

100m-177mm@30° x 1.32 = 234mm @ 0°

500m-165mm@30° x 1.32 = 218mm @ 0°

1000m-151mm@30°x 1.31 = 198mm @ 0°

2000m-121mm@30°x 1.30 = 157mm @ 0°

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

Panther Fibel lists slope effects for Panther 75mm APCBC, with 3.00x slope multiplier at 60° and 2.00x at 45°. If Panther gun penetrates 190mm at 0m/0° than slope effect of 3.00x results in 63mm penetration at 60°. U.S. slope effect for T/D=0.84 (63/75) and 60° is 3.10, which also is very close to Panther Fibel.

If Panther slope multiplier is 2.00 at 45° with 190mm penetration at 0°, 45° penetration is 95mm and T/D = 1.27. U.S. slope effect at 45° and T/D = 1.27 is 1.85, very close to Panther Fibel result of 2.00.

This, of course, is based on premise that Germans tested Panther gun against armor quality close to U.S. and British and reported actual slope effects they found.

If memory serves me, Panther Fibel presents different slope effect data than Tiger Fibel

and we assume that Panther Fibel is the real thing, and alot of other German slope effects are assumed figures that disregard T/D effects.

Above exercise suggests that Panther Fibel slope effects are based on 190mm penetration at 0° against Allied quality armor plate.

It is possible that Germans tested Panther gun againt recreated Allied armor because Germans reproduced hard T34 armor and shot their 37mm and 50mm ammo against it, we have report.

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

We use DeMarre from U.S. 75mm M61 times 1.158 for German APCBC penetration data, which results in 88L71 penetration of 219mm at 500m and 175mm at 2000m.

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

When two homogeneous armor plates are placed in contact, naval test data suggests that the effective thickness of the two plates is less than the combined thickness. Material in outer plate around hole can be pushed out of way in radial direction without much resistance from inner plate, other than some friction.

This may decrease Sherman jumbo armor resistance if it consists of two plates in contact.

Two face-hardened plates in contact resist like a greater thickness of face-hardened, which may be due to thicker total face-hardened layer in two plates than one single. PzKpfw IIIH front hull gained by having two 30mm face-hardened in contact.

Crusader matched regular and hard armor in contact, which added to overall resistance.

If someone will provide Sherman jumbo glacis and turret front armor we will examine whether 88L71 could penetrate and at what range, based on DeMarre estimate times 1.158.

[Guest Rob/1]

Woow where are you geting all this from?

[rexford]

We have had access to original WW II documents through National Technical Information Service, Bovington Museum, Canadian sources and some data from Germany.

At one point we had many WW II reports from U.S. Navy regarding 76mm APCBC penetration, and shatter gap.

Analysis of data was accomplished over a 20 year period.

We also collected articles from alot of different mags, including naval journals.

88L71 was very close to failure area during German tests, due to excessive stresses on projectile. BIOS report not only goes into armor but presents penetration data from tests.

Germans used very best rounds during penetration tests and admitted that service rounds used in battle were inferior. German penetration data gives two curves, best quality and service.

Uncapped German 50mm AP shatter failed in tests.

[Dittohead]

From the previous thread the numbers Jentz used were in question.

<BLOCKQUOTE>quote:</font><HR>For comparison:

Penetration at 30 degrees when using Pzgr.39:

______CM_____Jentz_____

range

100m 177mm 202mm

500m 165mm 185mm

1000m 151mm 165mm

2000m 121mm 132mm<HR></BLOCKQUOTE>

So your numbers for 30 deg match what CM models, not what Jentz used.

[Ari Maenpaa]

Thanks for the analysis Rexford. High quality post as usual.

Basing on this it seems that CM's penetration values for 88L71 are pretty much on spot:

CM v1.1b24

rnge penetration @0^

100m 220mm

500m 205mm

1000 188mm

2000 157mm

Although at the further end CM's L71 seems to be losing momentum rapidly when compared to DeMarre estimation (157mm <> 175mm).

Ari

[This message has been edited by Ari Maenpaa (edited 01-04-2001).]

[Jeff Duquette]

were penetration values up'd in the latest patch? I havent downloaded it as I'm in the middle of an PBEM operation.

[PzKpfw 1]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Jeff Duquette:

were penetration values up'd in the latest patch? I havent downloaded it as I'm in the middle of an PBEM operation.<HR></BLOCKQUOTE>

Good question Jeff since my HD crashed & was damaged i can't realy run anything cept the net & mail etc, so I can't even reinstall CM till i get a new HD (sometime after Xmas bills paid up).

So according to Rex converted 30^ data to US 0^ results the KwK.43 penetration @ 0^ would be :

100m - 234mm

500m - 218mm

1000m - 198mm

2000m - 157mm

CM's current 0^ pen data is:

100m - 220mm

500m - 205mm

1000 - 188mm

2000 - 157mm

So the question remains on the 30^ penetration for the KwK.43 concerning Jentz's German test data for 30^ results & whether or not the KwK.43 could penetrate 202mm @ 100m Ie:

100m - 202mm

500m - 185mm

1000m -165mm

2000m -132mm

Regards, John Waters

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

"We've got the finest tanks in the world. We just love to see the

German Royal Tiger come up on the field".

Lt.Gen. George S. Patton, Jr. February 1945.

[This message has been edited by PzKpfw 1 (edited 01-04-2001).]

[JoePrivate]

<BLOCKQUOTE>quote:</font><HR>were penetration values up'd in the latest patch? I havent downloaded it as I'm in the middle of an PBEM operation.<HR></BLOCKQUOTE>

No they are still the same.

[rexford]

German 30° stats for 88L71 are:

100m-203mm

500m-185mm

1000m-165mm

2000m-132mm

These 30° figures result in some really large values when U.S. slope effects are applied. Key issue is that German penetration at 30° is based on best quality rounds and ammo used in field, the service rounds, were inferior by about 5% to 7% (BIOS report gives penetration for best quality and service rounds used by Germans).

88L71 penetration at 0° may also be increased artificially since armor at 200mm or 180mm thickness may have less resistance per mm than thinner armor.

88L71 30° data is subject to so many factors that we don't like to use it, it seems too high. 203mm at 30° converts to about 270mm at 0°, which is way high compared to what we believe is realistic.

We use data generated by DeMarre equation estimate from U.S. 75mm APCBC multiplied by 1.158.

88L71 penetration of Jumbo's occurs because:

1. Jumbo mantlet armor has cast piece,which loses resistance compared to rolled

2. Armor is two pieces in contact, which is weaker than one plate with same thickness

3. Penetration can occur when average penetration is below effective armor resistance because penetration probability is 50% when penetration=resistance, and changes slowly as penetration moves slightly below resistance value (175mm penetration will penetrate 179mm on 1/3 to 2/5 of hits).

Armor and projectiles vary in effectiveness and impact velocity, which accounts for above noted situation. Think of it this way, penetration and armor resistance computations yield "average" values of each and variations occur. Penetration must be much greater than armor resistance for 100% penetration chance.

[Vanir]

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

Key issue is that German penetration at 30° is based on best quality rounds and ammo used in field, the service rounds, were inferior by about 5% to 7% (BIOS report gives penetration for best quality and service rounds used by Germans).<HR></BLOCKQUOTE>

Ya know, if you had been around here a couple of months ago, you could have saved some people a lot of time and effort writing hundereds of posts about the 88L71. If correct this does explain a few things.

Where oh where is Paul Labowski

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

You've never heard music until you've heard the bleating of a gut-shot cesspooler. -Mark IV

[rexford]

We don't use German penetration data for 30° except for service rounds, but there is issue that their test plate may be 10% better than U.S. best quality armor.

We have British penetration for Panther and Tiger at 30° against what looks like allied test plate, we converted 30° penetration to 0° and Panther does 190mm at 0° at point blank. Then we used DeMarre equation and German data on velocity vs. range to estimate penetration by other APCBC. 88L71 APCBC does about 230mm at 0° and 0m based on above thread.

We are happy with above procedure since it has been shown in allied tests that German 75mm outpenetrates U.S. 75mm at same velocity and angle, and 16% German advantage is in line with harder projectile nose (61 Rockwell C for average German round, 56 for U.S.).

[PzKpfw 1]

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

88L71 30° data is subject to so many factors that we don't like to use it, it seems too high. 203mm at 30° converts to about 270mm at 0°, which is way high compared to what we believe is realistic.

<HR></BLOCKQUOTE>

Rex, I'm familiar with German test methods Ie, best quality rounds, & best plate etc. Could you explain what you feel is wrong with the German test results & or procedures to us.

And post what you believe the 8.8 cm KwK.43 was capable of in Penetration useing normal service rounds Ie, Pzgr.39/44 & why it was incapable of achieving 202mm @ 100m @ 30^ etc, in laymans terms for us.

Regards, John Waters

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

"We've got the finest tanks in the world. We just love to see the

German Royal Tiger come up on the field".

Lt.Gen. George S. Patton, Jr. February 1945.

[rexford]

Why published German penetration data at 30° may not be valid for battle use:

1.

200mm thick armor probably has less resistance per mm than a 100mm plate, because it is very soft compared to 100mm.

2.

Penetration data based on test ammo, service round would have less penetration and this is what 88L71 penetration in field is based on.

3.

If Panther 75mm can penetrate 190mm of U.S. or British test plate at 0m/0°, DeMarre for 88L71 at 0m comes to about 235mm. Since slope multiplier for 88L71 is about 1.3 against thick plates at 30°, divide 235mm by 1.3 to obtain about 181mm/30° for penetration of allied test plate at 0m. By coincidence this is close to 177mm at 30° and 100m, but purely coincidence.

Coming up with German, Soviet and alot of British penetration figures is science, art, speculation and detective work, all rolled into one. What seems reasonable is the bottom line. We feel like Kojak, Columbo and Law And Order.

Penetration ranges based on our figures generally agree with Jentz' ranges or anecdotes. 75L48 penetrates T34 hull front out to some impressive range, Soviet guns penetrate Tiger II side and rear to ranges that are very close to what Jentz has for Russian experience and test firings.

[aka_tom_w]

No official BTS comment on this thread yet??

Rexford,

GREAT research! I still fascinated by all this new accuracy and penetration data WOW.

When can we see all your spread sheets and penetration data publically posted or available? Are you interested in sharing all this info with Charles? Is he interested in looking at it? Maybe some of it will be handy for CM2?

It looks like there is a great deal of new info that you ahve there.

Thanks again.

-tom w

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

[Guest Big Time Software]

Hi Tom:

<BLOCKQUOTE>quote:</font><HR>No official BTS comment on this thread yet??<HR></BLOCKQUOTE>

OK, I guess we can say something

It is nice to see that there is another team of researchers/mathematicians/Columbos out there just as dedicated to figuring out the "most likely truth" as much as we are. It is of course extra nice that these guys (as spoken for by Rexford) have come up with roughly the same values that we arrived at, using a totally different methodology, and completely independently from us. When any scientific study is corroborated in such a way, a mixed cheer of joy and sigh of relief is always felt. The former because it is nice to see someone else coming at the problem from a different angle, and the latter because it comes to a similar conclusion

In this particular case, one of the conclusions is that the German figures that Jentz quoted (the ones that spawned a few hundred posts in at least 2 threads!) are most likely too high for the 88L71.

We also want to thank Rexford for detailing the Jumbo mantlet's makeup (two separate plates) as it pointed to a mistake in CM, which made it stronger than the real thing.

Thanks,

Steve

[This message has been edited by Big Time Software (edited 01-08-2001).]

[hnh3_cm]

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