rexford Posted August 22, 2003 Share Posted August 22, 2003 The British report on "German 75mm and 88mm APCBC Ammunition at Oblique Angle", Department of Tank Design Report No. M.6914A/4 No.1 provides test data at 45 and 55 degrees from vertical. Converting the data to performance against vertical armor provides some interesting insights into relative effectiveness. A graph in the report presents the following penetration figures for 88mm APCBC, which are then converted to performance at the Tiger and Tiger II muzzle velocities (2558 and 3280 fps) against vertical plate using U.S. slope effect curves and the DeMarre equation: ========================= 88mm Large HE Capacity APCBC 65mm at 55 degrees & 2750 fps => 135mm at vertical and 2558 fps 58mm at 55 degrees & 2310 fps => 150mm at vertical and 2558 fps 62mm at 45 degrees & 2060 fps => 139mm at vertical and 2558 fps Average = 141mm vertical at 2558 fps ========================= 88mm Small HE Capacity APCBC 81mm at 55 degrees & 2965 fps => 160mm at vertical and 2558 fps 76mm at 55 degrees & 2887 fps => 154mm at vertical and 2558 fps 57mm at 55 degrees & 2220 fps => 156mm at vertical and 2558 fps Average = 157mm vertical at 2558 fps ========================= Note that the small capacity 88mm round outpenetrates the large capacity ammo by about 11%. Following converts small capacity data to 3280 fps muzzle velocity of 88L71 gun: ========================= 88mm Small HE Capacity APCBC 81mm at 55 degrees & 2965 fps => 228mm at vertical and 3280 fps 76mm at 55 degrees & 2887 fps => 220mm at vertical and 3280 fps 57mm at 55 degrees & 2220 fps => 223mm at vertical and 3280 fps Average = 224mm vertical at 3280 fps ========================= Curves are presented for 17 pdr APCBC penetration vs velocity against 45 and 55 degree plate (2900 fps is muzzle velocity of gun firing APCBC): =================== 17 pdr APCBC Solid Shot 82mm at 55 degrees and 2900 fps => 209mm at vertical and 2900 fps 100mm at 45 degrees and 2850 fps => 182mm at vertical and 2900 fps =================== Notable that 17 pdr APCBC is not going to pierce the Panther glacis on other than an occasional hit at 100m and beyond, if hits take place on level ground and do not strike highly vulnerable spots (weld lines, MG mount and ball, driver visor area). The penetration data at 55 degrees results in a vertical estimate which appears to be high, while the 45 degree figure is in line with published figures against vertical armor. 17 pdr APCBC appears to outpenetrate large capacity 88mm APCBC at 45 and 55 degrees by a considerable amount, which may be due to the following combination of factors: 1. solid shot vs HE burster yields greater penetration at all angles 2. British claim 17 pdr APCBC projectile nose is harder, increasing penetration Data is also presented for German 75mm very small HE capacity APCBC: ============================= 75mm Very Small HE Capacity APCBC 58mm at 55 degrees and 2440 fps => 138mm at vertical & 2460 fps 62mm at 45 degrees and less than 2099 fps => above 130mm at vertical & 2460 fps ============================= The vertical penetration estimates for 75L48 APCBC at 2460 fps are consistent with the figures developed using the German equations presented in the BIOS report, while the penetration figures for small capacity 88mm APCBC are lower than the BIOS material predicts. Jeff Duquette deserves much credit for finding the abovenoted British report and pointing others toward the valuable work. 0 Quote Link to comment Share on other sites More sharing options...
rexford Posted August 22, 2003 Author Share Posted August 22, 2003 The following notes provide some additional details on the subject firing tests: 1. report is held by the British Public Records Office (PRO) 2. U.S. armor slope curves are based on an analysis of slope effect vs impact angle and T/D ratio (plate thickness/projectile diameter) 3. Projectile weights and HE burster capacity is as follows: 88mm large capacity APCBC: 9.6 kg and 1.65% of weight is HE filling 88mm small capacity APCBC: 10.1 kg and 0.65% of weight is HE filling 75mm very small capacity APCBC: 6.8 kg and 0.20% of weight is HE filling Report indicates that large capacity 88mm ammo is used by Flak 36 and Tiger guns, whereas small capacity is fired by Tiger II and Pak 43. Other references have Tiger I firing small capacity 88mm rounds (German ballistic tables list 88L56 APCBC at 10 kg weight, with 10.2 kg for 88L71 APCBC). 4. 88mm projectiles are single piece monobloc (the main projectile body) whereas 75mm APCBC is two piece with a welded on nose. 5. U.S. firing tests with welded nose projectiles indicated that the round was superior to monobloc rounds at high impact angle, since the nose would break off and allow the ammunition to penetrate intact (single piece rounds would suffer much nose damage, increasing the limit velocity above the two piece rounds). However, past discussions on welded nose German APCBC indicated that 75mm APCBC two-piece shells were heat treated in such a manner that the welded nose did not result in superior performance at high angle (Jeff Duquette contributed the welded nose info if I am not mistaken). The British firing tests with 88mm and 75mm APCBC suggest that German welded nose ammo had about the same sloped armor performance as one piece projectiles would have. 0 Quote Link to comment Share on other sites More sharing options...
kipanderson Posted August 22, 2003 Share Posted August 22, 2003 Rexford, hi, Very interesting stuff as always. In this case it all seems to confirm what would have been expected. There is a clear trade off between penetration and HE content. My view had always been that penetration should be the priority, which today it is of course. Having seen up close what a “partial penetration” of a Tiger1 front plate looks like, Bovington Tank Museum has a 17pdr shot round stuck in a 100mm plate, I can tell you even without the HE fill rounds coming through in the 75mm class is “very bad news”. All the best, Kip. 0 Quote Link to comment Share on other sites More sharing options...
rexford Posted August 23, 2003 Author Share Posted August 23, 2003 The British report indicates that at 45 and 55 degrees impact, none of the German rounds penetrated in a condition where the HE burster would work. So, at high angles the German HE filled ammo was just like a solid shot except for the loss of penetration and added work that the HE filler entailed. 0 Quote Link to comment Share on other sites More sharing options...
rexford Posted August 23, 2003 Author Share Posted August 23, 2003 Some time ago Jeff Duquette shared a graph with me that provided penetration figures for 17 pdr APCBC at angles from 0 to 70 degrees, with extrapolation to 75 degrees (rolled homogeneous armor). The vertical penetration is a bit higher than we estimate, 187mm vs 177mm at 0m. The British penetration figures were presented to 600, 1000 and 1500 yards and we extrapolated the data to 0m and 2900 fps impact velocity. The following analysis compares the slope effects for the British data at 0m with the estimates generated by our equation for U.S. APCBC slope effect: 0 degrees, 187mm penetration, 1.00 slope effect 20 degrees, 173mm penetration, 1.08 actual and 1.11 predicted slope effect 30 degrees, 150mm penetration, 1.25 actual and 1.29 predicted 40 degrees, 115mm penetration, 1.63 actual and 1.59 predicted 45 degrees, 101mm penetration, 1.85 actual and 1.82 predicted 50 degrees, 88mm penetration, 2.13 actual and 2.12 predicted 55 degrees, 77mm penetration, 2.43 actual and 2.51 predicted 60 degrees, 66mm penetration, 2.83 actual and 2.97 predicted 65 degrees, 56mm penetration, 3.34 actual and 3.36 predicted 70 degrees, 50mm penetration, 3.74 actual and 4.41 predicted ============================================= Extrapolated penetration data at angle: 75 degrees, 38mm penetration, 4.92 actual and 5.22 predicted The 17 pdr APCBC slope effects follow the U.S. curve fairly closely except at 70 degrees. 17 pdr APCBC penetration at 55 degrees and 0m set at 77mm from British curves, compared to 82mm on curve in test report for German 75mm and 88mm APCBC at oblique angles. In the absence of a low probability success (or hits on weld line, machine gun port, previous hit gouge, etc.), 17 pdr APCBC will not penetrate Panther glacis at any range on level ground. Our analysis of flaw effect for Panther glacis versus 17 pdr APCBC indicates a 0.95 multiplier, which improves British gun performance a little but still results in low success probability. 0 Quote Link to comment Share on other sites More sharing options...
rexford Posted August 23, 2003 Author Share Posted August 23, 2003 Some time ago Miles Krogfus shared a number of British Ordnance Board graphs with me for German 50mm APC, 75mm very small capacity HE APCBC and 88mm APCBC with small and large HE capacity. Going back over the graphs after estimating the vertical penetration of 75mm and 88mm ammo from trials at 45 and 55 degrees, the graphs are in close agreement with the estimates from oblique hits: VERTICAL PENETRATION ESTIMATES 75mm small capacity APCBC at 750 m/s (PzKpfw IVH muzzle velocity) 137mm from oblique hit 140mm from British O.B. curve 88mm small capacity APCBC at 780 m/s (Tiger muzzle velocity) 157mm from oblique hits 157mm from British O.B. curve 88mm large capacity APCBC at 780 m/s (Tiger muzzle velocity) 141mm from oblique hits 138mm from British O.B. curve 88mm small capacity APCBC at 1000 m/s (Tiger II muzzle velocity) 224mm from oblique hits 220mm from British O.B. curve ========================== 50mm APC at 2240 fps (PzKpfw IIIG muzzle velocity) 76mm from British O.B. curve 50mm APC at 2700 fps (PzKPfw IIIL muzzle velocity) 99mm from British O.B. curve The consistency of the British Ordnance Board curves with the estimates from oblique hits suggests that the O.B. curves may have been based on firing tests. 0 Quote Link to comment Share on other sites More sharing options...
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