rexford Posted January 7, 2001 Share Posted January 7, 2001 Due to variations in powder charge, armor resistance and projectile metal quality, penetration vs. armor resistance is not an "all or nothing" situation. WW II Russian penetration data presented on Potapov's site has about a 12% variation between the 20% and 80% penetration probability figures. What this means in statistical terms is that a round must have about 20% more penetration than the average armor resistance to succeed 100% of time, and that penetrations are still possible when penetration is 20% less than armor resistance. This is in line with reports in Potapov site that Soviet ammo quality varied alot. If a Tiger has 103mm at 0° effective armor resistance on the driver plate, than hits with 120mm average penetration at range will sometimes fail and hits with 82mm penetration will sometimes succeed. The exact percentages can be calculated from normal distribution curves (bell shaped probability curve). U.S. penetration test scatter during WW II showed that if penetration exceeded armor resistance by less than about 12%, some hits would fail. And hits with 10% less penetration than armor resistance would sometimes pass thru. U.S. armor and projectile consistency during tests was better than Russian. When penetration = armor resistance, 50% succeed and 50% fail. The ballistic limit is found by averaging the highest velocity failure with the lowest velocity success, if the difference is within a certain figure. Link to comment Share on other sites More sharing options...
Jarmo Posted January 7, 2001 Share Posted January 7, 2001 Seems in line with what I see in CM. Although I'm not so sure about the underpowered penetration. Link to comment Share on other sites More sharing options...
rexford Posted January 7, 2001 Author Share Posted January 7, 2001 Following data from Potapov site illustrates Soviet ammo case: 76.2mm L41.5 APBC at 500m: Penetrates 75mm 80% of time at 0° Penetrates 84mm 20% of time at 0° Calculated 50% penetration is 79mm. 100% penetration requires about 58mm effective armor at 500m, 0% penetration against 100mm effective. If this round hits 80mm Tiger side at 500m, penetration probability is 44% with 79mm average penetration. When 88L71 (174mm penetration at 0°) hits Sherman Jumbo glacis at 2000 (179mm at 0° resistance), penetration probability is about 24%. Link to comment Share on other sites More sharing options...
rexford Posted January 7, 2001 Author Share Posted January 7, 2001 Assuming that CM considers actual lateral angle from firer to target armor that is hit, say a T34/76 during 1943 fires on the Tiger 80mm side armor with a 10° lateral angle to armor perpendicular. T34 round has 80mm penetration at 0° at range of shot. Tiger armor resistance equivalent to about 82mm at 0° (slope effect at 10° = 1.03), which barely exceeds 76.2 penetration at 0°. Penetration/effective armor ratio is 80/82, or 0.98. 39% of hits penetrate. Say that T34 hit Tiger 80mm at same range but effective armor was 88mm at 0°, about a 20° angle from armor perpendicular to gun barrel. Penetration/effective armor ratio is 0.91, and about 10% of hits penetrate. Potapov site says that Russian ammo quality improved during 1944 and 1945, say standard deviation drops from 7% to 3.5%. When penetration/ratio is 0.91 during 1944 combat, penetration probability will be 1/2%, one of every 200 hits will penetrate. Whereas, during 1943 20 of every 200 hits would penetrate. Armor rules have long struggled with the lateral shot angle issue. TANK CHARTS gave effective armor resistance at shots taken at 0° and 45° to hull or turret facing. Some board games in the 1980's placed a template over the target vehicle and identified the lateral hit angle, and individual tank cards gace effective armor at lateral angle. The T34 has 45mm armor at 40° on the hull superstructure side. If a 75mmL48 hits this on a direct side shot (0° angle from hull side perpendicular), the effective armor resistance is about 67mm at 0° (we'll forget about high hardness effects for now). Say the 75mmL48 hits the side superstructure at a 45° lateral angle to side hull perpendicular. Compound angle is combination of 40° from vertical and 45° from perpendicular, for 57° hit angle. 45mm at 57° under attack by 75mm APCBC has a slope effect of 2.5, so effective armor resistance is 45mm x 2.5, or 112mm at 0°. If 75L48 has 108mm penetration at 0° on above hit, penetration/effective armor ratio is 0.96 and penetration probability will be about 23%. Penetration and armor resistance figures are AVERAGE values from tests and they vary from shot to shot, so under-penetration can still result in a success. This type of calculation thread is best accomplished on a spreadsheet or with pre-programmed equations that include slope effect vs. angle and T/D ratio. Link to comment Share on other sites More sharing options...
StellarRat Posted January 7, 2001 Share Posted January 7, 2001 Hey Rexford, You seem to be the resident ballistics expert on this forum. I can't remember the formula that determines the effective armor thickness if you are shooting at sloped armor. I seem to recall it having something to do with sine or cosine. Do you have it? [This message has been edited by StellarRat (edited 01-07-2001).] Link to comment Share on other sites More sharing options...
rexford Posted January 8, 2001 Author Share Posted January 8, 2001 Slope multiplier is a function of angle and T/D ratio, and varies from one ammo type to another. APCBC is different from AP which is different from APBC. And tungsten core is another story alotgether. Link to comment Share on other sites More sharing options...
hnh3_cm Posted January 8, 2001 Share Posted January 8, 2001 anti-spam bump Link to comment Share on other sites More sharing options...
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