rexford

Figures presented in CM for 75mm Sherman penetration appear to be solid AP shot, which may not have been primary anti-tank round during 1944 and 1945. TM-9-1907 lists APCBC-HE penetration as 91mm at 0m and 82mm at 500m. We've seen pictures of 75mm AP in France but solid shot seems to be in the minority. 75mm solid AP shattered alot in North Africa, and U.S. converted AP rounds to something else (APCBC-HE) to save material that would otherwise have been lost. Was 75mm AP a training round by France?

CM lists 110mm turret front, does game account for rounded mantlet where impact angles can vary from 0° to about 65° or 70° at top and bottom of round armor. Also curious if ricochet thru hull top probabilities account for bending of small rounds as they bounce off thick armor (high T/D), which decreases chance of a hull top penetration. This would address comment on whether 37mm APCBC ricochet penetrates Panther hull top alot.

The hit at about 45° penetrates the plate and heads downward after defeating the armor. The hit at a greater angle from vertical (the lower picture) faces too much effective armor resistance and drives into the plate and is pushed upward, plate wins and projectile loses. The defeat angle looks lile about 55° or 60° from vertical. Whether or not a ricochet results depends on effective resistance of armor compared to penetration of projectile. Hits at an angle win by pushing a plug out of the armor, the round follows the plug.

Why published German penetration data at 30° may not be valid for battle use: 1. 200mm thick armor probably has less resistance per mm than a 100mm plate, because it is very soft compared to 100mm. 2. Penetration data based on test ammo, service round would have less penetration and this is what 88L71 penetration in field is based on. 3. If Panther 75mm can penetrate 190mm of U.S. or British test plate at 0m/0°, DeMarre for 88L71 at 0m comes to about 235mm. Since slope multiplier for 88L71 is about 1.3 against thick plates at 30°, divide 235mm by 1.3 to obtain about 181mm/30° for penetration of allied test plate at 0m. By coincidence this is close to 177mm at 30° and 100m, but purely coincidence. Coming up with German, Soviet and alot of British penetration figures is science, art, speculation and detective work, all rolled into one. What seems reasonable is the bottom line. We feel like Kojak, Columbo and Law And Order. Penetration ranges based on our figures generally agree with Jentz' ranges or anecdotes. 75L48 penetrates T34 hull front out to some impressive range, Soviet guns penetrate Tiger II side and rear to ranges that are very close to what Jentz has for Russian experience and test firings.

Rounds basically ricochet because penetration isn't sufficient to accomplish plate defeat. If penetration is sufficient, rounds almost always go thru unless one of the factors that don't show up on the firing range raises its' head.

Machineman's post shows that when round hits armor with fair slope it penetrates downward. Americans were so afraid of Tigers that they often identified PzKpfw IV's as Tigers. 88mm Flak was an anti-tank gun to a Sherman tanker. Unless someone went up to enemy position and made positive ID it was often impossible to verify battle accounts. What makes 4 hits in 4 shots by M18 at 2000 yards a lucky string is that 95.5% of shots would be within 4' vertically of aim point, so hitting StuG on one shot entails some luck at 2000 yards. M18 commander called for lead based on 2 second flight time, it actually was 2.8 seconds to target. Still made four straight hits.

Oops! Meant to say in last message that few or none of Panther hits on 20mm at 70° glacis at 0m to 2000m will fail to penetrate.

Rexford means King's Crossing, or King's Fiord. Grandfather was half Mohawk "indian" (native american} named Dexter who won a load of medals during WW I, and fought in all the major battles that America was part of (including Meuse-Argonne, I believe). Even won the Croix de Guerre, the French were happy when other people fought the Germans. Following presents muzzle velocities for British HE and smoke, which is an interesting addition to earlier discussions: 3" tank howitzer 600 fps HE!!!! 95mm tank howitzer 1050 fps HE & 746 fps smoke!!!!! 6 Pdr tank gun 2675 fps HE 75mm M3 1550 fps HE & 850 fps smoke 2100 fps super charge (good for shooting through bunker openings when pinpoint accuracy is needed). Hitting a vertical target with a 3" tank howitzer would be an adventure beyond close range, but tanks with this gun were called "close support". Low velocity of smoke suggests thin walls to allow max chemicals, so not too much stress. (aside: Firefly had 3x/6x interchangeale gun sight, makes sense to easily see and target long range targets) Why is 75mm HE so potent when 105mm HE is also low velocity? Don't know. The data presented in previous messages is official American data which appears to be from field tests, and we never pursued the why's any further. We would be interested in an explanation if anyone has or finds one. We had, and still may have German data on HE charge size within all of the tank gun shells. Here are German HE muzzle velocities: 50L60 550 m/s (1804 fps) Data goes out to 6500m!!!!(?) Long range HE bombardment by Puma's? 75L48 550 m/s (1804 fps) 75L70 700 m/s (2296 fps) 76.2L51.5 550 m/s (1804 fps) 88L56 810 m/s (2657 fps) 88L71 750 m/s (2460 fps) "88" HE muzzle velocities seem kind of high, must have been for hitting anti-tank guns on the fly. Low velocity for smoke is interesting, no pinpoint accuracy with that muzzle velocity. German ballistic data for HE shells gives longitudinal distance for 50% of shots. For 810 m/s 88L56 HE, "lange" for ground dispersion on level ground is 107m at 2000m, so if range estimation is perfect than 50% of shots fall within a 351' long distance centered on 2000m range and running along the firing line. Longitudinal scatter for 75L48 HE at 550 m/s is 54m at 2000m, or 50% of HE shots fall within a 177' long distance centered on 2000m and running along the firing line. The longitudinal fall of shot is due to fact that flat trajectories are heavily influenced by vertical scatter, while lower velocities are not as impacted. 3" British howitzer at 600 fps or 75L24 HE would have a very small longitudinal dispersion about 2000m range if it followed the abovenoted German trend. How far afield do German HE rounds fall from the intended point: 50% of 75L48 HE shots at 2000m will fall within 1.6m of firing line after jump and other factors are cranked in. HE shots should not fall 100m left or right of target, under normal circumstances. For those who are interested in ballistics, William Jurens wrote a paper entitled EXTERIOR BALLISTICS WITH BALLISTICS that is the single best work on the subject, in our opinion. Has drag coefficients, equations and a computer program in BASIC that computes elevation, angle, etc. for shots and prints out results every 50m or so. The paper ran in a naval magazine, and an internet search on Mr. Jurens' name might identify a current source (we haven't had time to do this). The paper covers naval rounds and it is easy to apply findings to WW II anti-tank stuff.

U.S. 76mm APCBC steel shell vs HVAP tungsten core. This is from U.S. penetration data: 100m APCBC-131 HVAP- 232 500m APCBC-119 HVAP-205 1000m APCBC-106 HVAP-174 2000m APCBC-84 HVAP-127 3000m APCBC-67 HVAP-92 HVAP loses penetration faster but still ends up with more penetration. HVAP is also more accurate due to flatter trajectory. The big difference is the slope effect. At 55°, HVAP multiplier is 3.25, APCBC will be lower against armor thickness based on T/D. HVAP slope effect is not influenced by T/D. HVAP is brittle and tends to break against sloped armor, which is why multiplier is so high. How does one estimate velocity vs. range, use the DeMarre equation. If a round has 130mm penetration at 0m and 92mm at 1000m, moving terms around in DeMarre equation indicates that velocity ratio at range is proportional to penetration ratio raised to 0.7 power. (92/130) raised to 0.7 power is 0.785, so if muzzle velocity is 2600 fps than estimated velocity at 1000m is 0.785 x 2600 fps, or 2041. We use this all the time and it works reasonably well for almost all ammo, including HVAP but with a little less accuracy (but results still reasonable). Soviet APBC flat nose rounds have three different velocity regions where the power number changes drastically. Pushing a flat nose through a plate at high velocity is alot easier than at low speed, due to shape, whereas pointed or rounded noses have less drastic changes between high and low velocity (although they still do and using one 0.7 exponent on penetration ratio is a simplification. We have read all of Okun's work and correspond with him. His work on plates in contact was used to estimate Sherman Jumbo resistance. If velocity squared in DeMarre equation is equal to plate thickness raised to 1.4 power times a bunch of irritating constants, then taking the square root shows that velocity is proportional to penetration T raised to 0.7 power. This is powerful and lets one estimate striking velocity vs range for almost any round if one om velocity and penetration and penetration data vs. range.

Long ago we read that 17 pounder HE was not especially potent due to high muzzle velocity, and Advanced Squad Leader was going to treat 17 pounder HE as something smaller. The best HE comes from the low velocity guns. 75L24. 75L40. German high velo guns fire HE at reduced speed. We did a study and while high velocity is needed to hit vertical targets, low speed was better against a group of infantry in a field because flat trajectory fall on ground is highly influenced by vertical dispersion. Got to attack infantry crossing a field, bring on the close support 75L24. 75L24 could also fire cannister at human wave attacks due to absence of muzzle brake. And low velocity guns can indirect fire against relatively close targets, Panther can't. That is one reason why low speed howitzers are so valuable, big HE load and able to pop one in on a target with high arc fire.

Here is probability data for chance that effective HE fragments will hit 6 square foot target: 20' distance 100% for 75 and 105 80% for 90 67% for 76 35' distance 38% for 105 30% for 75 22% for 90 18% for 76 50' distance 19% for 105 13% for 75 10% for 90 8% for 76 100' distance 4.1% for 105 2.2% for 75 1.9% for 90 1.6% for 76mm 200' distance 0.8% for 105 0.4% for 75 and 90 0.3% for 76 Data comes from a TM that U.S. published during WW II, doesn't have title or number on the pages I have. Also shows blast shape and size, and armor penetration.

We don't use German penetration data for 30° except for service rounds, but there is issue that their test plate may be 10% better than U.S. best quality armor. We have British penetration for Panther and Tiger at 30° against what looks like allied test plate, we converted 30° penetration to 0° and Panther does 190mm at 0° at point blank. Then we used DeMarre equation and German data on velocity vs. range to estimate penetration by other APCBC. 88L71 APCBC does about 230mm at 0° and 0m based on above thread. We are happy with above procedure since it has been shown in allied tests that German 75mm outpenetrates U.S. 75mm at same velocity and angle, and 16% German advantage is in line with harder projectile nose (61 Rockwell C for average German round, 56 for U.S.).

Really good question, and one that goes beyond normal conclusions. They may be more to it than my previous answer considered. A 60° angle from vertical does not automatically mean that a certain percentage of hits will ricochet off. When 75mm APCBC from a Panther hits a 20mm at 70° plate, will most of the rounds bounce off because of the angle? In penetration tests of U.S. APCBC, 20mm at 70° is equivalent to 50mm at 0° when it is hit by 75mm rounds. A round that can defeat 50mm at 0° angle (vertical plate) on half the hits during tests will penetrate 20mm at 70° at the same velocity and range. At 2000m the Panther round will be descending onto the target if ground is level, so 20mm at 70° will resist like less than 50mm at vertical, and every Panther hit should penetrate. Will 100% of hits penetrate? The answer is probably "no", because some projectiles may lose stability in the air for any number of reasons and wobble, which decreases penetration capability. Air turbulence, worn guns that provide little spin to the round, bent guns due to recent hits, etc. German tests showed that putting spare tracks on 70° angled armor could disrupt the projectile motion enough to make a big dent in the penetration, which is why so many PzKpfw IVH carry spare tracks on the 72°glacis (this area of the pzKpfw IVH is very vulnerable to penetration by the Sherman 75mm). It is safe to say that most, no, practically all Panther hits on 20mm at 70° from 0m to 2000m will penetrate. Angle alone is not enough to guarantee protection, although I have seen wargames where it was assumed that all hits at 70° or greater would bounce. TOBRUK had a hit resolution table where 30% or more of the 88mm Flak hits on the Stuart side armor would fail to damage the tank, due to angle and other considerations. U.S. penetration data clearly shows that 70° and 75° slope armor can be penetrated, and naval test data shows the same result for up to 85°. Penetration data is based on test firing at close range with the velocity that is expected at a given range. They don't put a target at 3500m and fire 88L71 at it. At 2000m and greater ranges alot of things will occur that don't occur when one tests 2000m penetration using a 100m long firing range and reduced velocity. This is also why penetration data against highly sloped armor does not include descent angle effects, because they conduct the firing at a range where descent angle isn't a factor. Below 600m range, test firing data should closely match battlefield experience because fewer odd things occur. But consider wind. If a 30 mph wind is blowing directly at a Tiger I as it shoots, that retards the round and lowers the impact velocity. Cross winds of 25 mph can also help create ammo wobble or hits at angles that don't occur on the short firing range. In a similar vein, will 37mm APCBC hits on the lower Panther mantlet penetrate the hull top on ricochets as often as 76mm. No. 37mm rounds are long and thin, and bend alot easier than 76mm. When 37mm hits the Panther mantlet bottom and bounces, it is likely to do so after bending the nose and losing flight stability. Husky 76mm rounds are better able to hit and bounce without severe structural or aerodynamic disruption because of size. Bent noses and funny flight paths due to shape changes decrease the chance that the Panther hull top will be penetrated. There is an awful lot to armor penetration, but it is not the physics that is the killer, it is the natural phenomena that play games with data based on 100m shooting and is extrapolated to 3000m. Ricochets off the Panther mantlet bottom fall into the aforementioned category. What % of 76mm hits off the mantlet bottom will penetrate, what percentage will do nothing/ No one knows the answer, but it probably isn't 100% and may not be 0% either. Some 76mm hits on the mantlet bottom will have sub-par steel and will end up with bent noses. Softer Panther mantlet steel will allow the round to dig in more, so the round loses energy and may not ricochet at all, or will bend or even shatter. There are no tests on this and alot of odd events that can spoil a prediction. Angle alone will not cause a high percentage of ricochets, if it did we would see alot of 15mm at 80° glacis plates.

U.S. 76mm HE was grossly inferior to 75mm HE, and the following stats provide ample evidence of the differences: 75mm HE 3120 fps initial fragment speed 950 effective fragments at 20' from blast 105mm HE 3500 fps initial fragment speed 1010 effective fragments at 20' from blast 76mm HE 2260 fps initial fragment speed 560 effective fragments at 20' from blast 90mm HE 2900 fps initial fragment speed 672 effective fragments at 20' from blast What the above data shows is that 75mm HE from the Sherman was almost as effective as 105mm howitzer HE, and quite superior to 76mm and 90mm HE. There are benefits to having a low muzzle velocity (we have heard that low velocity means less need for thick walls on HE shells, which allows more HE< but we are not sure on this). The German 75mmL24 may have had similar benefits with regard to HE effectiveness when compared to 75L48 and 75L70. Short barrels shoot high potency HE. Shermans with the 75mm gun were handy anti-personnel weapons regardless of what one might say about the APCBC.

If CM does not attempt to model actual gun scatter in lateral and vertical directions, maybe this is why CM hit %'s are different than calculated figures using trajectory. Does CM consider range estimation error?

Regarding penetration probability, Russians tested ammo for 20% and 80% penetration probability. Average of two figures is 50% success thickness.

Slope effects are a function of the T/D ratio for a particular type of ammo, such as APCBC (T is armor thickness, D is projectile diameter for steel rounds). Why T/D? When a hammer hits a thick wall it may bounce off without a dent, whereas the same force may blow a plug of material out of a thin wall. The thicker the wall relative to the projectile diameter, the more material pushing back on the shot and the harder it is to penetrate. When 50mmL42 APC from PzKpfw III in Russia hit KV side turret wall, they bounced off without a visible dent. T/D was very high and too much material to even push the surface very far. Rounds penetrate sloped armor by pushing out a plug and following the plug down through the armor. This is very difficult to model with physics but easier to model using published penetration data. Analysis of tests shows that T/D and angle are the factors that matter. U.S. Army Technical Manual TM-9-1907 has penetration data vs. angle and range for APCBC and HVAP. British NPL report has slope equations for AP, as does TM-9-1907. We have U.S. test of 122mm APBC with flat nose, based on captured IS-2m gun and turret from Berlin. Really low slope effect since projectile doesn't have a nose and noses: 1. bend on impact, absorbing energy 2. hit the walls as projectile moves thru plug, using energy The only real way to predict slope effect is to analyze penetration data and plot results vs. T/D for particular angles. When Panther 75mmL70 APCBC hits 63mm at 60° from vertical (30° from horizontal), slope multiplier is 3.1!!!!!!!! This means that a round that can penetrate 190mm at 0° (vertical armor) can also penetrate 63mm at 60° from vertical at same velocity. Both armors will have same equivalent thickness. This is how slope effect or multipliers are calculated from penetration data, find penetration at 500m vs. 0° vertical, find penetration at 500m vs. 60°, divide 0° penetration by 60° penetration and that is the multiplier that converts 60° penetration to 0°. Note T/D ratio for 60° penetration and plot slope effect at 60° vs. T/D ratio. If slope effect = T/(cosine(angle)) raised to 1.43 then 60° slope effect is 2.69, which is too low for Panther vs. T/D = 0.84 (63/75). Most of the slope multipliers in published documents are based on a single data point, such as slope effect at 500m, because it is hard work plotting multiplier vs. T/D and results cannot be easily presented to non-technical types. British reports state that slope effect is function of many factors including plate thickness and projectile diameter. We plotted slope effect vs. T/D vs. angle for different ammo types using equations fit thru data, and it takes about 12 graphs to do everything including tungsten rounds. The spreadsheet takes data on projectile, armor thickness and compound angle (result of lateral and vertical angles taken together to form a single angle) and cranks out the slope effect and then compares everything to penetration at 0° and range, and says whether it penetrates or not. Since penetration data is based on 50% success when penetration at 0° = equivalent armor resistance at 0°, penetrations can occur when penetration is less than resistance and shots can bounce when penetration exceeds resistance. Think of it this way, penetration and armor resistance calculations represent AVERAGE values and variations occur in almost all projectiles and armor. Three hits on the same armor in different areas with similar angles can result in three different results.

Our spreadsheet can define projectile shot placement to within a very small area and the placement is then measured out on a model. If settings are exactly the same on the next shot, the round placement will change due to shot-to-shot dispersion variations. Measuring on a model gives a better result with regard to hits on odd shapes or potentially damaging ricochets.

A 100m lateral aim error at 2200m range equates to 2.6° error, or 0.0454 radians or 45.4 mils error. 45.4 mils is a very large aim error. Would it still be on the gun sight?

Germans trained to aim at center of turret/hull meeting point, Americans usually aimed at center of mass but July '44 training manual change said to aim at weak areas. Germans published booklets for gunners that identified weak areas, Panther and Tiger Fibel (bible) was given to tankers with enemy weak points identified. Tiger I mantlet a real difficult target for 17 pounder, hull front is easier. Problem is that tankers in combat may forget training and just try for hits, even if they bounce. Germans were most effective at training crews to target weak areas like turret/hull meeting line. 37mm Pak crewman in one message recently said that they automatically fired at turret/hull line due to kills on even a heavy tank like KV-1, and they were trained to do it.

17 pounder APDS fired at 4000 fps, which yields flat trajectory and good accuracy even given velocity loss with range. The problem is that field tests showed that about 50% of APDS was wild and lost penetration due to unbalance round. IN thoery, the sabot falls off as the round leaves the barrel, in actual practice pieces of the sabot would stick to the round jerking it to one side and decreasing penetration due to funny hit angle. During American tests during 8/44 at Isigny France, APDS missed Panthers in open at several hundred yards and didn't pierce glacis, while previous British tests showed ammo to be accurate and it penetrated Panther glacis at 700 yards. APDS was new during 1944 and inconsistent. Russians T62 was supposed to be greatest tank in world during 1973 war, smooth barrel gun with muzzle velocity over 5000 fps and APFSDS round. Round had discarding sabot like 17 pounder but used smooth bore gun for added velocity. Instead of gaining accuracy through spinning round (rifling does this), Soviet 115mm APFSDS released fins as it left barrel which were supposed to obtain true and straight flight that rifling normally buys. Problem was that fins often came at different times which unbalanced ammo. Israeli's reported that T62 rounds would strike the ground at odd angles or sideways. New APDS is an adventure.

German 30° stats for 88L71 are: 100m-203mm 500m-185mm 1000m-165mm 2000m-132mm These 30° figures result in some really large values when U.S. slope effects are applied. Key issue is that German penetration at 30° is based on best quality rounds and ammo used in field, the service rounds, were inferior by about 5% to 7% (BIOS report gives penetration for best quality and service rounds used by Germans). 88L71 penetration at 0° may also be increased artificially since armor at 200mm or 180mm thickness may have less resistance per mm than thinner armor. 88L71 30° data is subject to so many factors that we don't like to use it, it seems too high. 203mm at 30° converts to about 270mm at 0°, which is way high compared to what we believe is realistic. We use data generated by DeMarre equation estimate from U.S. 75mm APCBC multiplied by 1.158. 88L71 penetration of Jumbo's occurs because: 1. Jumbo mantlet armor has cast piece,which loses resistance compared to rolled 2. Armor is two pieces in contact, which is weaker than one plate with same thickness 3. Penetration can occur when average penetration is below effective armor resistance because penetration probability is 50% when penetration=resistance, and changes slowly as penetration moves slightly below resistance value (175mm penetration will penetrate 179mm on 1/3 to 2/5 of hits). Armor and projectiles vary in effectiveness and impact velocity, which accounts for above noted situation. Think of it this way, penetration and armor resistance computations yield "average" values of each and variations occur. Penetration must be much greater than armor resistance for 100% penetration chance.

When penetration is within a few percentage points of armor resistance, from 1/3 to 2/5 of hits might still penetrate, since 50% penetrate when penetration = resistance. 175/179 = 98% ratio, so penetration is still possible. Penetration data for everyone but Soviets is the armor thickness that can be defeated on half the hits. We use 0° angle as a right angle hit, with angle of plate measured from vertical. This is what U.S. used during WW II, and Brits too. When they give 30° penetration figures it is for a plate 30° from vertical. U.S. tests show that angle does not induce ricochets. If 60° penetration is 90mm and 90mm armor at 60° is hit, 50% penetrate and 50% don't. But there is a penetration value where 100% will penetrate 60° slope armor and none will bounce. 88L71 lateral dispersion at 2000m predicts that 50% of shot scatter will be within 0.7m of aim, and 95.5% will be within 2m of aim point. 50m and 100m lateral misses at 2000m with 88L71 seem to require an explanation since they indicate that the gunner is badly overcorrecting. A 100m lateral miss is 328' left or right, which is longer than a football field. If the 88L71 is aimed at the tank and corrected, it should be closer than 50m from aim point.

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