German Ammo Versus Sloped Plate

[rexford]

Thanks to excellent research efforts by Jeff Duquette, who found one of the key firing test resports for WW II ammo performance, we just received a British firing test report from WW II where German rounds were fired at 45° and 55° sloped plates:

88L71 APCBC penetrates 80.8mm @ 55° at 2965 fps

75L48 APCBC penetrates 57.8mm @ 55° at 2440 fps

Our book relates an 88L71 hit on 80.8mm/55° to 201mm at 0° resistance, which 88L71 penetrates at 1094m. Estimated impact velocity at 1094m is 2929 fps, so data in our book closely matches actual British test for 88L71 (2929 vs 2965).

75mm hit on 57.8mm/55° is equivalent to 137mm at 0°, which 75L48 penetrates at 33m. Velocity at 33m is 2446 fps, very close to British result (2446 vs 2440).

British test uses large HE filler cavity 88L56 round, which appears to penetrate alot less armor than Tiger ammo (which was small capacity). Large capacity 88L56 ammo would be used by 88mm Flak prior to Tiger introduction, based on our research (with further reports welcome as we do not claim finality on this issue).

Report is from British Public Records Office (PRO), where it is held, and is WO 194/749.

There are many other test results including 17 pounder APCBC against 25mm at 75° armor, which is penetrated at about the same velocity that our book estimates. We just started to analyze the data.

British report comments on wide variations in plate resistance which are not related to armor hardness, and our initial review indicates that standard deviation is about 5%. If a round has 5% more penetration than armor resistance it will succeed on about 84% of hits, and 10% greater penetration succeeds on about 98% of hits. A hit where penetration is 5% less than armor resistance will succeed about 16% of time.

[ 10-05-2001: Message edited by: rexford ]

[rexford]

For 88L71 APCBC vs. 75.87mm at 55°, test velocity is 2882 fps for 50% success.

Our book relates that armor and angle to 185mm at 0° resistance, which would be penetrated by 88L71 at 1680m.

British test velocity of 2882 fps against 75.87mm/55° is associated with 1300m range.

The disparity between theoretical and actual penetration range in the above case is due to wide variations in armor plate resistance, where plate/projectile combination limited 88L71 penetration to a shorter range than normal.

Due to greater resistance than average, 88L71 APCBC needed 195mm penetration to defeat 185mm resistance on half the hits (plate resistance was 5.4% higher than average).