Interpreting Russian Penetration Data

[rexford]

The ARTKOM equation presented in Miles Krogfus' AFV News article on DeMarre and ARTKOM (May-Aug 2003) explains the basis for Russian penetration figures and calculated estimates.

Some additional insights can be obtained through analysis of published Russian penetration figures for 76.2mm ammunition, which have been provided by Vasiliy Fofanov on Yahoo! Tankers forum site (with the same figures available on Russian Battlefield and other Internet sites).

76.2mm APBC BR-350A

CP Penetration for 80% Success Probability

80mm at 100m, 76mm at 300m, 70mm at 500m and 63mm at 1000m

76.2mm APBC BR-350B

CP Penetration for 80% Success Probability

86m at 100m, 81mm at 300m, 75mm at 500m and 68mm at 1000m

Using the ARTKOM equation with the appropriate constants and shell factors from Miles' article, along with an assumed velocity-range curve, one obtains (80% success):

76.2mm BR-350A

75mm at 100m, 72mm at 300m, 68mm at 500m and 61mm at 1000m

76.2mm BR-350B

79mm at 100m, 76mm at 300m, 72mm at 500m and 64mm at 1000m

The Russian firing tests for both rounds exceed the ARTKOM equation estimates by an average of 4.6% for BR-350A (range is 2.9% to 6.9%) and 6.5% for BR-350B (range is 4.2% to 8.9%).

How to interpret the apparent variations?

Miles' article indicated that production fluctuations could result in the penetration constant ranging from 2300 to 2500 for a round with an average constant of 2400 like BR-350B. If the Russian firing trials used 2300 constant ammo instead ot the typical or average 2400, the penetration estimates from the ARTKOM equation would be increased by 6.3%.

One explanation is a random variation in the projectile "quality" used in the tests, where the guns fired above average rounds.

Another possibility is the normalization of the ARTKOM equation, where the penetration of all rounds was forced to fit the DeMarre equation. If the actual relationship between penetration and velocity was different from the DeMarre equation, the 76.2mm APBC may have penetrated more than the equation predicted but a "one size fits all" equation may have glossed over some of the differences.

Looking at 76.2mm APBC versus 85mm APBC, about 40% of the 76.2mm round diameter is "flat nose" as opposed to about 20% for 85mm APBC. Perhaps a wide flat or blunt area increases the face-hardened penetration.

If the Russian firing test results are for 2400 constant ammo, the 76.2mm APBC BR-350B penetrates 75mm at 500m on 80% of the hits, or about 79mm at 500m on half the hits. So even at the higher test firing figures, 76.2mm APBC would not routinely penetrate an 80mm face-hardened plate.

While the ARTKOM equation predicts 111mm at 500m, 102mm at 1000m 93mm at 1500m and 85mm at 2000m for 85mm APBC, the Russian firing tests resulted in:

105mm at 500m (ARTKOM estimate higher by 5.7%)

100mm at 1000m (higher by 2%)

92mm at 1500m (higher by 1%)

85mm at 2000m (no difference)

Oddly enough, the 85mm AP penetration estimates from firing tests are very close to the figures for 85mm APBC at every range, suggesting that someone may have used the same velocity-range profile for 85mm AP and APBC.

[rexford]

Miles Krogfus' article on the DeMarre Equation and ARTKOM provided some eye-opening insights into what the Russian penetration figures mean, namely that they are not pegged to medium hardness homogeneous armor plate.

The article is not specific about the meaning of high hardness armor, and suggests, if one reads into the text, that high hardness is related to face-hardened armor. The Germans switching from high hardness to homogeneous armor is consistent with face-hardened to homogeneous armor, while high hardness homogeneous to medium hardness homogeneous would not.

In reality, the appearance of Tiger tanks was a major transition from the face-hardened armor which had previously appeared on front of PzKpfw III and IV and StuG III, where all the plates on Tiger were homogeneous. While the initial Panther D and Panther A which the Russians fought appear to have carried face-hardened armor, information provided by Lawrence Sims some time ago indicated that Panther production went with all homogeneous armor types starting late 1943.

A German Intelligence report on the SU 85 provides Russian penetration data for 85mm APBC (119mm at 100m, 111mm at 500m, 102mm at 1000m, etc.) with an explanation for the Russian data, which I translated to mean:

"the penetration is calculated from the formula Jacob de Marre for a cemented armor plate using the coefficient K=2400." Plate is described as "eine zementier te panzerplatten".

Converting the penetration figures to velocities using the ARTKOM equation and a constant of 2400 closely matches the assumed velocity-range profile for 85mm APBC.

If the ARTKOM estimates are assumed to be against cemented or face-hardened it adds to the usefulness of Miles' article.

The 76.2mm APBC BR-350B would penetrate 76mm face-hardened at 500m, 68mm at 1000m and 54mm at 2000m. The 50mm face-hardened armor on the front of PzKpfw III and IV, and StuG III, would be vulnerable at the 1500m range and beyond. But a PzKpfw IVH with 80mm frontal armor would be a hard nut to crack at 500m.

The ARTKOM equation predicts 165mm penetration for 122mm AP (BR-471) at 0m, which is for 80% success. Converting to 50% success results in 175mm (1.06 multiplier).

By way of comparison with Allied AP rounds and their ratio's of face-hardened to medium hardness homogeneous armor penetration, 122mm AP might penetrate about 201mm of vertical homogeneous armor at 0m. And 170m homogeneous at 700m.

An 85mm homogeneous Panther glacis at 55 degrees from vertical would resist 122mm AP hits like 177mm vertical, which would result in a small percentage of 122mm AP hits at 700m succeeding. This is consistent with the reports on the initial combat between IS-2 and Panther, where penetrations at 600m and 700m were obtained with many ricochets (see Russian Battlefield article on IS-2 development).

[JasonC]

The 6% difference looks suspiciously like a 50% to 80% correction factor.

The default, obvious way to understand a specification of hard armor in a Russian test is Russian steel, which is homogeneous hard (high brinell), not face hardened. Unless a test specifies use of captured German tanks as targets, the Russians had their own steel for test plate, not German steel.

The continual assumption that any Russian penetration report or data that indicates possible success against any sort of 80mm plate at any range must reflect "magic bullet" ammo, above that normally available, is tendentious reasoning, for which there is -no- evidence. Specifically, it is pure gratituous speculation that rounds used in any of the "offending" reports were above the average. That above average rounds existed may be true, but there has been no indication they were involved in any cited case.

Moreover, dispersal in results on the order of 10% from round to round are to be expected without any change in ammo or armor quality. Reports of such dispersion in observed penetration are commonplaces, and some have been advanced here recently (as though due to armor quality, when shot to shot variation is obviously present).

Some reports of failure and some reports of success at similar ranges, angles, plates etc, are to be expected. They do not need an additional layer of explanation, claiming ordinary rounds could not penetrate and only superior ones (purely hypothetical as to their actual use in the reported cases discussed) could.

"It never works, unless it does" is "data indistinguishable" from "it sometimes works and sometimes doesn't". The Occam's razor explanation is that the round's penetration is marginally capable of defeating 80mm, that therefore some do and some do not, that therefore some reports show failure and others show success, with no magical difference in round quality or mistakes about test plates or any of the rest of it.

Meanwhile, the only reports of consistent failure regardless of range and angle stem from a report containing a known physical impossibility - failure of PAK 40 with German ammo at 500m flat against 80mm vertical. Which is about as credible as 45mm kills from the front.

The Tiger lobby is grasping at straws.

Meanwhile, I showed some time ago that taking the Russian battlefield site figures - which are quite close to existing CMBB penetration numbers printed in the charts, as opposed to observed "shell broke up" behavior seen in CMBB today - literally, one would find the level of effective protection of the Tiger I close to absolute in practice, anyway.

Specifically, shots from random locations distributed evenly within 1 km of a Tiger I would be expected to fail at least 96% of the time. Even with R-B 350B numbers. Actually, considering the fact I use IP numbers to measure "penetration possible" side angles and ranges, it could be as high as 99% protection (since IP range means only 1/5 gets in).

Only a minority of shots within tiny side and rear lobes of limited side angle and close range could partially penetrate. The closer half of the 1 km range envelope is 1 part in 4. The flat angle lobes are about 1 part in 5. IP means 1 penetration in 5. Even without track hits or weighting forward arc and more distant ranges more heavily (for live shooters), that means 1/100 is the right order of magnitude to fufill all 3, with a random shooting location.

Tigers were perfectly effective on the British sector of Normandy against 75mm gun tanks, which all conceed were theoretically capable of penetrating the sides with a low enough side angle. It is simply very hard, tactically, to get low side angle, short range shots within tiny vunerable lobes.

Notice also that Russians report liking LL short 75 Shermans for interior comfort and especially mechanical reliability. They were perfectly willing to praise LL equipment in those areas they considered it superior. But there is no trace of them saying "finally we had a gun that could kill a StuG or a Panzer IV".

The US 75mm is clearly superior to a Russian 76mm firing 350A ammo, as early in the war. But by R-B numbers, once the 76s have 350B there is little to choose between them. The US gun may be marginally better, but only marginally. As they are guns of about the same muzzle energy and once the Russians have 350B both are capped, that is hardly surprising.

If the US gun was markedly superior in the most common match ups (vs. IVs and StuGs), don't you think they would have noticed? Every CMBO player knows how routinely US 75mm tanks handled StuGs and Pz IVs out to medium range. Every CMBB player knows by now how invunerable a StuG is to Russian 76mm from the front.

If the difference between a short 75 Sherman and a T-34/76 was "routinely effective to 1000m" and "almost never effective even at point blank", shouldn't there be a record of it in Russian comments about LL Shermans? Wouldn't it have been slightly more noticable and worthy of comment than a comfy seat cushion?

Attempting to eradicate even the tiny vunerable lobes has resulted in ahistorical results like the uberStuG, of which there is no trace even in German tactical claims. German StuG aces attribute their own success to superior gunnery, getting in the first shot and the first hit, better optics, superior range, firing from well camoed ambush, and hull down use of the StuGs low profile.

There is no need for the straw grasping, the magic Russian bullet theories (heat treated for tests only, or reported kills only), the armor quality difference assumptions (that "hard" means face hardened, etc). Tigers would be effective in the hands of anyone not tactically incompetent without any such nonsense. We do not need the crutch. Anybody who does can't drive.

[ May 04, 2003, 01:16 PM: Message edited by: JasonC ]

[PzKpfw 1]

Originally posted by JasonC:

The default, obvious way to understand a specification of hard armor in a Russian test is Russian steel, which is homogeneous hard (high brinell), not face hardened. Unless a test specifies use of captured German tanks as targets, the Russians had their own steel for test plate, not German steel.

Their is evidence that the Soviets use of the term High hardness may have been to identify German Face Hardened armor Ie:

Throughout 1943 tests against German Tigers, Panthers, Ferdinands, and other new tanks and assault guns caused ARTKOM to realize that a change from high hardness to homogeneous plate was occuring in German tanks. Thus in 1944 a graph was published that showed the performance of guns of Soviet and lend lease tanks versus current German armor plate

*See: Krogfus Miles. De Marre and ARTKOM p.18

The article also tells that ARTKOM 122mm BR-471 calculations vs German Panther armor produced the same striking velocity of glacis penetration as the actual BR-471 Panther glacis defeat's striking velocity in the live fire tests @ Kubinka.

This new data strongly implies that Soviet wartime penetration data was calculated based on German armor type, not vs domestic plate.

Concerning Soviet test plate the fact is we have no idea what the composition was. Miles who has done more research on this then most useing actual documents, instead of say, unsubstatiated opinion, as some posters here are fond of useing, states the Soviets used *High hardness ballistic plate. He does not identify type of armor plate used.

*See: ibid. p.18

Valera on the RBF states*:

Unfortunately, the armor quality (hardness etc)usually missed in those reports, so I cannot reveal it's real quality. All what is mentioned is "homogenous hardened armor" or simply "homogenous armor" and nothing more.

*See: http://www.battlefield.ru/guns/defin_4.html

So Jason if you have an refrence that identifies the armor composition quality,of Soviet test plate armor, empericly as homogeneous etc, please cite it, I'm sure Miles etc will want to aquire a copy of your refrence.

Regards, John Waters

[ May 05, 2003, 11:22 PM: Message edited by: PzKpfw 1 ]

[rexford]

Jason C stated: "The continual assumption that any Russian penetration report or data that indicates possible success against any sort of 80mm plate at any range must reflect "magic bullet" ammo, above that normally available, is tendentious reasoning, for which there is -no- evidence. Specifically, it is pure gratituous speculation that rounds used in any of the "offending" reports were above the average. That above average rounds existed may be true, but there has been no indication they were involved in any cited case.

"

Horsefeathers.

Miles Krogfus' article clearly states that some of the BR-350B APBC were routinely heat treated for better penetration.

In addition, the tests against Tiger II were conducted against the turret side, hull side and hull rear, and the penetration ranges were all consistent with an added 10% penetration.

Anyway, you're never going to admit that we are being fair about things and that everything can be explained in a reasonable manner.

And even if way above average BR-350B defeated the Tiger II, it still points out that average BR-350B could fail against the Tiger side, as well as below average.

Lorrin

[PzKpfw 1]

As to the use of rounds in cited cases , the fact is not 1 cited case presented here, identifies round type used in tests except the 1st LF tests conducted in April 25 - 30th 1943, these identify the 76.2 rounds used as *BR-350A, & BR-350B.

*See: Krogfus Miles. De Marre and ARTKOM

p.17

The available data on the September tests identify weapon type but, but not round type except concerning the 57mm & 85mm as obtaining penetrations useing an improved round.

The available data concerning later tests concerning 76.2mm fireing vs various other German tanks, do not identify round type they state Ie, domestic ammunition.

Most publications can't even agree on 76.2mm IMV, Ie, sources on the BR-350A MV state 662m/sec, 676m/sec etc, while ARTKOM BR-350A calculations appear to have been derived useing an IMV of 655m/sec.

Regards, John Waters

[ May 05, 2003, 03:26 PM: Message edited by: PzKpfw 1 ]

[Redwolf]

Bump.

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[dieseltaylor]

Lest we forget .....