rexford
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Posts posted by rexford
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See my post on Isigny tests, the 0.85 quality multiplier for Panther glacis does not appear to be warranted against front lower hull nose armor, the cast mantlet or hull side.
Armor flaws on Panther and Tiger II appear to be tied into the large size of the glacis plates and the hardness (above 250 Brinell), which made armor more susceptible to heat treatment errors in Germany than smaller plates or cast.
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American tests in France conducted during August '44, against 3 captured Panthers, are summarized below, with some important conclusions regarding CM combat results:
1. Guns aimed at glacis from 200 to 800 yards range, following accuracy is based on % of shots striking glacis:
76 HVAP 83%
17 pounder APCBC 87%
17 pounder APDS 53%
2. American crews said 76 HVAP was most accurate ammo they had ever fired, hit % slightly smaller than 17 pdr APCBC but spread of shots around aim point may have been smaller.
3. 3 penetrations of exposed glacis/nose weld line in 56 glacis hits, weld line resistance to penetration about 68% of what good quality glacis would generate.
4. 2 of 13 hits by 17 pounder APCBC crack glacis, follow-up hits near crack penetrate due to lowered resistance. Hits that crack glacis have about 73% of penetration needed to fully pierce good quality plate.
5. 76 HVAP penetrates glacis once at 200 yards on 6 hits, no other Panther glacis defeats by HVAP.
6. No penetrations of hull MG on 56 glacis hits, only 1 hit on MG port and it bounced.
7. Panther nose armor resists penetration like good quality plate without flaws, even on Panthers with defective glacis armor. 2 of 3 76 HVAP hits on nose at 400 yards penetrate, both nose hits at 600 yards bounce.
Theoretical nose resistance at 600 yards equals 60 x 3.35 slope effect for 55°, or about 200mm at 0°, and 76 HVAP penetration in U.S. tests is 202mm at 0° so about half hits should bounce.
0.85 modifier for sub-quality armor does not appear to apply to Panther nose, based on analysis of all hits against Panther nose (front lower hull).
8. 2 of 3 Panthers exhibit defective glacis armor, 1 glacis reacts like good quality plate.
9. Hits near cracks on Panther glacis indicate that hits resisted with 65% of good quality resistance.
CONCLUSIONS
1.
0.85 multiplier for inferior Panther glacis armor appears to be warranted after comparing penetration figures to armor resistance with slope effects.
2.
Front lower hull nose armor resisted like good quality armor and did not exhibit the lowered penetration resistance, or a tendency to crack, like the glacis. This suggests that the 0.85 modifier should only apply to Panther glacis.
The above conclusion is supported by other U.S. test results, where Panther mantlet resisted 76mm APCBC hits like good quality cast armor and the side hull armor did not show significant differences from good quality armor resistance.
The poor resistance of the Panther glacis has been attributed to the size and hardness of the plate, and the timed quenching procedures adopted by the Germans to substitute for rare alloys such as Nickel. Nickel allows armor treatment to generate good quality armor with variations in treatment from standards, Germans used multi-quench treatment instead of Nickel but it was sensitive to a few seconds variation and the bigger the plate the greater the chance for defective armor.
We believe that the Tiger II and Panther glacis armor was consistently poor, but smaller plates and cast on the rest of the tank did not show poor resistance.
Put another way, if cast Tiger mantlet armor was generally of good quality, why would Panther cast mantlets be consistently defective during the same time period. And if PzKpfw IVH 80mm rolled armor was generally good quality (did not require a multiplier like 0.90 or 0.85), why would Panther side hull be consistently poor.
The only difference between Panther armor and other tanks with good quality plate was the size of the glacis. Jagd Panther lowered the hardness of the glacis from 280 Brinell on Panther to 220 Brinell on Jagd Panther, which appears to have eliminated most or all of the substandard resistance problems (low hardness may be easier to consistently heat treat).
Our analysis suggests that large German armor areas with Brinell Hardness over 250 had consistently poor resistance, other areas were good.
3.
Tests support slope effects in U.S. firing tests of 76 HVAP, 3.33x at 55° while CM has 2.87x at 60°.
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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.
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75L48 muzzle velocity of 770 m/s could be a random variation from 750 m/s average.
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At Isigny France, 8 hits by APDS at 400 yards on Panther glacis, 1 penetration.
76 HVAP penetrated Panther glacis at 200 yards, 1 penetration in 6 hits on glacis.
Panther glacis resistance is 80 x 3.35 slope effect, or 268mm at 0°. 76 HVAP penetration is 227mm at 0°, penetration/resistance ratio is 227/268, or 0.85.
Combination on low quality armor and low probability penetration resulted in 76 HVAP penetration.
CM slope effects for HVAP would seem to warrant re-examination.
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Research on the impact of armor flaws resulted in multipliers that convert poor armor to an equivalent thickness of good quality U.S. 240 BHN test plate.
Example:
If a round penetrates 100mm of U.S. good quality test plate and penetrated 120mm of flawed plate at the same angle and velocity, the 120mm plate would have a quality factor of 100/120, or 83%.
Further research showed that the flaw effect was proportional to T/D ratio and influenced by impact angle, where plates that are thick relative to projectile diameter are able to spread impact around better and suffer less from flaws.
If a Panther glacis with medium flaws is hit by 90mm APCBC, the Quality multiplier for 55° hits would be 0.89. Against 122mm APBC, the Quality multiplier for Panther glacis would be 0.85.
When medium flaw Tiger 80mm armor is hit by 75mm rounds, T/D = 1.07, angle is 0° and quality multiplier is 0.98, so 75mm hits do not result in a significant reduction in armor resistance in this case.
Armor flaws is different from weak spots due to weld lines or shot traps.
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During August of 1944, the U.S. conducted firing tests on 3 captured Panthers using a variety of guns and ammo, including 17 pounder APDS.
The ammo proved to be wildy inaccurate. Of 13 shots aimed at the Panther glacis at 200 and 300 yards, only 7 hit the target. 1 penetration occurred.
Only 1 of 7 glacis hits penetrated at 200 and 300 yards.
The inaccuracy and inability to consistently penetrate were attributed to unbalanced rounds due to uneven shedding of sabot pieces.
British observers noted that in earlier trials at Balleroy, 2 hits out of 4 on the Panther glacis penetrated at 700 yards.
British penetration data for 17 pounder APDS is at 30°, using U.S. HVAP slope effects the 700 yard penetration at 0° would be 245mm.
The Panther glacis armor is 80mm @ 55° which is equivalent to 268mm at 0° using U.S. firing test HVAP slope effects.
If 17 pounder APDS penetrated Panther glacis on half the hits at 700 yards, this may approximate the ballistic limit and the armor quality vs. APDS would be (245/268), or 0.91 when penetration = effective armor resistance.
This analysis suggests that 17 pounder APDS can be modelled with U.S. firing test HVAP slope effects, which exceed CM figures. The results also support the theory that APDS was inconsistent and could vary widely in accuracy and penetration, sometimes failing to penetrate at 200 yards and then penetrating on half the hits at 700 yards.
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We use U.S. HVAP slope effects for all tungsten core, since tungsten brittleness makes slope multipliers greater than steel.
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APDS slope effects might be close to HVAP.
Plus about half of APDS shots might go astray and lose penetration due to uneven shed of sabot pieces.
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Just about run out of things to say.
Would like game to be about the same as our rules, cause it is easier to play with computer tanks, infantry and scenery than maneuver scale models on my bed and then have a stray infantryman stick into my back late at night.
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CM slope effect for 76 HVAP vs 47mm armor at 60° is 2.1, U.S. test data results in 4.3 estimate. CM also shows HVAP slope multiplier changing with T/D, firing test data shows that it remains constant.
Panther glacis resistance to 76 HVAP will be about twice what CM predicts, 55° slope effect for HVAP should be 3.3.
This is something else that needs fixin'.
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It appears that our data was based on von Senger after reviewing other published studies. 75L48 at 750, 75L46 Pak at 792 is what our data is based on.
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Excuse my ignorance of computer stuff, but how does one download game improvements and where are they found. The CM download page only listed one and people talk about alot of patches.
Thanks.
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Germans may have referred to 75L48 anti-tank gun as 75L46 to avoid confusion, with tank gun listed as 75L48.
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If 75L46 Pak penetrates 144mm at 0m/0° and 792 m/s, then 75L48 penetrates 133mm, and 75L43 penetrates 131mm. This is fairly consistent with figures we use.
Note that L43 to L48 barrel length increase only results in 10 m/s increase in muzzle velocity, + 1.3% velocity for 12% longer barrel. This may have lead authors to assume that muzzle velocities were in error and 75L48 should be 792 m/s.
German data clearly indicates in several different places that 75L48 was 750 m/s at muzzle. Maybe PzKpfw IVf2 and G were first tanks to carry 75L43 and powder charge reduced, PzKpfw IVH may have had stronger ring or earlier tanks proved that hull could hold 750 m/s and charge on 75L48 increased above 75L43 but still below 75L46.
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German projectile data sheet for 75L48 lists 750 m/s, which is what we use.
75L46 Pak has shorter barrel but may have had more powder charge, which is how we explain things. However, PzKpfw IVH turret ring not designed for large recoil forces, which limited the muzzle velocity of 75mm projectiles. Maybe 75L43 and 75L48 had reduced powder charges to safeguard turret ring and 75L46 had normal charge.
German penetration figures appear to be resolved by treating listed 75L48 penetration as really at 792 m/s (revision for 750 m/s would lower figures):
If 75L46 penetrates 144mm at 0m/0° and 792 m/s, then DeMarre for 0° and 0m has:
Panther 75mm penetrates 182mm at 935 m/s,
88L56 penetrates 157mm at 780 m/s,
88L71 penetrates 226mm at 1000 m/s.
Above figures for 88L56 and 75L70 are German muzzle velocities. The above DeMarre estimates may be slightly different from current CM figures at range.
PzKpfw IVG had 30mm face-hardened on top of 50mm face-hardened, CM lists 73mm armor which may be low.
Many WW II tanks had sad turret front and mantlet armor (PzKpfw IVH, IS-2m, Pershing, M4A3E8, etc.), and weak armor was due to turret unbalance due to gun weight.
Potapov article on IS tanks states that 122mm gun threw turret out of balance, and limited armor that turret front could carry.
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U.S. penetration test data for 76 HVAP shows 3.34 slope multiplier at 55° vs. 2.90" plate, and 3.40 slope multiplier at 55° vs. 2". Slope effect does not change with T/D.
300 yard penetration of Panther glacis by 76 HVAP in field test at Isigny, France, August '44.
Penetration at 300 yards is 2.63" at 55°, or 67mm. Armor is 80mm thick times 0.9 quality factor for 72mm effective.
Penetration ratio equals 67/72, or 0.93. Penetration probability about 20%, which is consistent with report on how shot penetrated glacis (paraphrased):
shot stuck in plate and stopped, then it suddenly pointed downward and entered the armor.
On subject of U.S. ammo penetration, tests of U.S. projectiles against a variety of plate appear to be consistent with TM-9-1907 data.
Fought battle with one Panther against 5 M5A1 with 37mm, Panther knocked out on frontal hit at 550m by penetration of weak spot in front lower hull armor. Guess one can't assume that 60mm armor is 37mm proof, even when 37mm penetration at 0° is less than plate thickness at 55°.
Shot probably hit rectangular weld line, which was noted to be vulnerable area.
Our studies of penetrations on Panther through front hull weld area, based on Allied firing tests, suggested that effective armor resistance was 2/3 computed, or about 100mm at 0°. Stuart 37mm probably didn't go thru here unless weld weakened by previous hits.
Interesting result.
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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.
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German data shows that 75L48 was fired at 750 m/s, 75L46 Pak 40 at 792 m/s.
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CM appears to seriously underestimate armor resistance versus HVAP, if U.S. tests are considered:
CM HVAP slope effect vs. 47mm at 60°
2000m range : 99 penetration at 0°, 47mm at 60°, for 2.11 slope multiplier at 60°
U.S. Test Data
1200m range: 173mm penetration at 0°, 51mm at 55°, for 3.40 slope effect at 55°
U.S. Technical Manual TM-9-1907 lists 133mm at 0° penetration for 76 HVAP at 2000m.
We estimate that 60° HVAP slope multiplier is 4.3, from regression equation for 0°-55° data, more than twice the figure in CM.
All U.S. tests for HVAP show slope multipliers that exceed APCBC by large amounts, and are significantly higher than CM.
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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?
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We assumed British would have tested service rounds found on a Panther, best quality ammo for plate proof tests would normally not be available at front.
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Did U.S. have HVAP during June '44?
M10 knocked out Panther at 500m with upper front hull penetration, which would only be possible with HVAP unless it went through MG port. M10 penetration data lists HVAP even though it may have been unavailable.
76mm HVAP slope effects in CM seem lower than U.S. test data. 76mm HVAP had 60° slope effect of 4.3 and it doesn't change with T/D ratio, CM slope effect at 60° is quite a bit lower and decreases with decreasing T/D. \
HVAP slope effect for 55° is about 3.3, so 60mm Panther front lower hull would have 3.3 x 60, or 198mm at 0° effective resistance to HVAP.
198mm front lower hull resistance would limit HVAP penetration range to about 600m.
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We had alot of British penetration charts, graphs and tables for Tiger I 88 and Panther 75 at 30°, and the penetration data was higher than any other data we had seen.
We converted the British 30° penetration to 0° using slope effect vs. T/D, and Panther penetrated 190mm at 0m/0°. The Demarre for 75L70 from CM 75L48 is a little higher than 190mm, suggesting that CM for 75L48 may be a tad high.
75L48 looks overstated, others look understated.
GERMAN PENETRATION DATA
in Combat Mission Archive #3 (2001)
Posted
If CM uses 50% as the penetration probability when listed penetration equals effective armor resistance, then a bell-shaped curve may already be assumed when penetration is above or below effective resistance.