rexford

Face-hardened armor has a thin surface layer that is very hard. The armor defeats uncapped AP by shattering or cracking the nose. Armor piercing caps have a fairly thick cap over the projectile nose and shoulder, with an air space directly above the vulnerable nose. This decreases the chance that face-hardened armor will crack the nose. Flat nose rounds spread their impact on face-hardened armor over a larger area, which is less likely to crack the armor. Some sources state that face-hardened armor does better against flat nose rounds. Russian APBC is also low nose hardness, which might further decrease performance against face-hardened plate. No one seems to know for sure if Russian APBC is good or bad against face-hardened plates. APBC would seem to have larger slope effects against face-hardened than homogeneous armor. We think. Russian APBC has a windscreen ballistic cap, German APCBC has the windscreen ballistic cap and an armor piercing cap.

At 500m, Russian 76.2mm APBC penetration at 60° is 41mm. At same range, German 75L48 APCBC penetration at 60° is 45mm. So 75L48 outpenetrates Russian 76.2 by 123 to 75 at 500m against vertical armor, but 60° difference is 45 to 41. The Russian APBC slope effects are based on homogeneous armor, where projectile dig in allows flat nose to rotate round into armor instead of away from plate (ricochet reaction). With face-hardened armor, success or defeat will occur within a short distance of surface, which may not allow nose dig in. Many German tanks use face-hardened armor which may not allow as much nose dig-in due to very hard surface layer, so we don't know if the APBC slope effects work against panzers such as PzKpfw III and IV (front) and Panther (side hull). No one seems able to provide data for Russian APBC against face-hardened armor. This is a serious data problem.

85mm APBC penetrates 145mm at 0° and 0m. Panther glacis resistance to 85mm APBC equals 182mm at 0° if good quality, 168mm at 0° with medium flaws. No 85mm APBC penetrations against Panther glacis, and since 76.2mm APBC has less penetration against vertical, nothing for that gun either. Hetzer 60mm at 60° resists 85mm and 76.2mm APBC hits like vertical plates of 145mm and 163mm, so no 85/76.2 APBC penetrations of good quality Hetzer glacis either. APBC has low slope effects but that doesn't make up for low nose hardness, which depresses penetration all-around. Hetzer is disliked due to tight fit of crew, and extremely vulnerable side armor. Plus gun didn't have a recoil mechanism, it was firmly attached to tank. In fact, Hetzer gun originally was same as 75L48 with a muzzle brake, but the lack of recoil mechanism caused wicked vibrations, so end of gun (with muzzle brake) sawed off. Shortened gun did not vibrate badly. Hetzer muzzle velocity in CM should be 750 m/s. APBC slope effect will make side armor on Panther, PzKpfw III and IV, StuG III and IV, etc. very vulnerable on wide angle hits.

And now for a taste of T34 superiority over the Sherman. The Russian Battlefield has an Archive report on comparative study of T34 and KV-1 at Aberdeen Proving Grounds. Russian 76.2mm was let loose on Sherman glacis, and penetrated it at 1100m!!!!!!!!! Based on our numbers, Sherman 75mm APCBC would bounce of T34 glacis at point blank!!! What gives, one might ask, since T34 penetration at 0° is inferior to Sherman 75. 1. Early Shermans have glacis with as many as EIGHT separate pieces welded together. Hit on or near a weld and resistance might drop. 2. Shermans use some cast pieces in glacis, and they have less resistance than rolled armor. 3. American armor very prone to flaws prior to late 1943 4. Russian 76.2 APBC penetrates less vertical armor than Sherman 75 but T34 gun penetrates ALOT MORE at high angles. This is due to wonderful flat nose rounds. Russian 76.2mm APBC penetrates about 40mm less vertical armor at 500m than American 76mm, but outpenetrates U.S. 76mm against 60° slope armor at that range. T34 glacis armor is probably easier to penetrate with German 75mm than Sherman, but face to face T34 gun wins hands down against targets with sloped armor. Unfortunately, Tiger has vertical armor, which brings T34 76.2 back to earth. Maybe Germans went for vertical armor on Tiger sides cause they knew (or guessed, or were lucky) about 76.2mm ability against sloped armor. Granted that every T34 hit on a Sherman glacis at 1100m would not penetrate, but between that test at Aberdeen and the ability of T34's to cut open PzKpfw IVF2's and G's things are not that bad.

APDS is not so good. Inaccurate quite a bit difficulty hitting targets in firing tests. Shatter fails if impact velocity too high. Decreases APCBC accuracy after APDS is fired. Has about twice the constant aim scatter of APCBC ammo. Not good. All it has going for it is low slope effects when it does work properly. But how confident would crews be when a properly aimed shot at a stationary target at 500 yards misses by a mile. Would you want to face down a Tiger II and have your life depend on APDS flying straight and true? And even if it did hit the turret front on a Tiger II, would it shatter into little pieces and anger the gunner.

Rex (The King) says: Thank you very much. And here is a little number I call Shatter Gap Hotel, and it sounds a little like this.....

Data table and discussion is presented on the Saumur Intranets site at following address http://musee-des-blindes.intranets.com/disc/default.asp?command=detail&id=6615&thread_id=6534&l_form_id= Log in as visitor, post should be under discussions, armor and projectiles, and then book errata page 6. Previous shatter gap threads dealt with steel projectiles, this tungsten business is something new that I found in a report last week. What sparked my interest is reading about how great tungsten ammo was, and how it was the end-all and be-all against German armor. APDS has a very high muzzle velocity and the hits appear to fall within shatter fail region quite often at close and medium range, which is CM country. U.S. HVAP has muzzle velocities much lower than APDS and the chance for a shatter failure against Tiger or Panther armor is restricted, compared to APDS. For those who hate technical hair splitting I have kept this thread simpler and in summary fashion. If one wants the details, go to Saumur Intranets and download the page with the table and write-up. What I found interesting is how we think we have got things pinned down, and along comes another really odd and off-the-wall anomaly. I previously thought the penetration failures with 17 pounder APDS were due to flight instability, then along comes critical shatter velocity and it fits much of the failure data when rounds have too much penetration. Did I detect a Mr. Bill accent in the "oh nooooooooo!" response. Well, rest assured that I have no plans to present endless technical posts that further refine intricate drawings on the head of a pin. Elvis has left the building, and that is all for now.

Just like steel projectiles, tungsten core ammo can fail if it has too much penetration. Test results presented in the report EFFECT OF IMPACT AND EXPLOSION show that tungsten ammo will fail if the velocity exceeds a critical value, which is a function of angle. So when 6 or 17 pounder APDS hits the Tiger front hull at 100m, the APDS core may shatter and fail. And when 76mm HVAP blasts into the curved areas on the Panther mantlet at close range, a shattered nose may defeat the hit. Based on the report text, hits that exceed the critical velocity abruptly increase the diameter of the penetration hole, which increases the velocity needed for penetration (more material thrown out of the way, more energy used). What proof that these lab test results actually show up on the battlefield? Glad you asked. Our book looks at APDS tests against Tiger tanks, and hits failed at velocities and angles that exceeded the critical velocity from the lab tests. And when hits succeeded, the velocities were below the critial velocity. Like your mother always said, too much of a good thing is no good, and sometimes having too much penetration spoils the broth. Or something like that. [ 07-14-2001: Message edited by: rexford ]

Sherman 75mm penetrates 81mm homogeneous armor at 500m and 95mm face-hardened. Tiger uses all homogeneous armor PzKpfw IVH is face-hardened on front Panther A and D hull side is face-hardened Tiger II curved 100mm mantlet is face-hardened StuG III appears to be face-hardened on front CM penetration data for Sherman 75 is inbetween TM9-1907 data against face-hardened and homogeneous, 89mm at 500m. So CM may overestimate Sherman 75 against all-homogeneous armor Tiger and homogeneous Tiger II side, and underestimate effectiveness against face-hardened targets. British tests of several different 75mm and 76.2mm rounds against their homogeneous armor resulted in the same homogeneous penetration for U.S. 75 and 76 as TM9-1907. The 10% greater penetration for Sherman 75 in CM compared to TM9-1907 data means that Sherman pierces Tiger 80mm side at 500m with side angles from 0° to 21° in CM (half hits penetrate criteria). I've lost ALOT of Tigers within that angle spread. If one goes with TM9-1907 data, Sherman 75mm at 500m has to hit Tiger 80mm side armor with side angles from 0° to 2° to penetrate on half the hits. On the wargame battlefield, Sherman 75 gains a big advantage against Tiger side armor if penetration is 89mm at 500m, compared to results with 81mm penetration at 500m. That 10% difference means a big change in the penetration angles (a much wider arc for successful hits). Our book analyzes Allied firing test data against Tiger and Panther and shows that German armor quality was the same as Allied penetration test plate. So U.S. and British penetration data can be directly compared to German armor. Not to appear too Tiger oriented, but our book also uses 82mm for Tiger side armor instead of 80mm. Every little bit helps, ya know. 82mm for Tiger side armor is only 2.5% more thickness, but if that is what the British measured, that is what they measured. Russians seem to use 82mm quite a bit too in their analyses. To be fair, our book presents actual measured thickness for 76mm armed Sherman mantlet, which is ALOT THICKER than the 89mm figure that is normally assumed. Russian armor is usually thinner than spec thickness when it is measured, but only for certain vehicles. [ 07-09-2001: Message edited by: rexford ]

The data in TM9-1907 for 40mm M81 penetration leads to the following slope multipliers at 2250 fps impact: Homogeneous Armor 1.15 at 30° Face-hardened Armor 1.19 at 30° 1.37 at 45° 1.82 at 60° AP rounds normally have slope effects over 1.25 for 30° and over 2.50 at 60° for the thicknesses penetrated by 40mm at 2250 fps. The above slope effects look like what would result from flat nosed rounds hitting sloped plate, rather than standard AP ammo. Anti-aircraft rounds with flat noses called "wad cutters" cause they knocked out a wad of armor when they hit. Local term.

Book is being sold now. Frederic Erk at Saumur Museum is handling European orders, I handle rest of world. Book review is available at following site, go to articles, articles and essays and then halfway down page. http://www.tabletoptactics.com/ For ordering info e-mail me at rexford179@cs.com or Frederic Erk at curator@musee-des-blindes.intranets.com Book is 136 pages text and about 64 other pages with graphs, drawings and tables. Thanks for interest.

Even though 40mm M81 AP doesn't have a flat nose there are similarities between that round and Russian APBC, which will be analyzed. The 40mm AP data may help estimate Russian APBC penetration and slope effects against face-hardened armor.

Never saw that Carlisle site before, great info! Thanks. 40mm M81 AP is for Bofors anti-aircraft gun, and has unusual nose and ogive shape. This helps our research quite a bit.

Penetration data for 40mm M81 AP suggests that it might be flat nose. 2 pounder AP penetrates about 87mm of homogeneous armor at 2600 fps and 2.375 pound weight, 40mm M81 AP penetrates 61mm at same velocity and 1.96 pounds. Both rounds are solid AP shot without caps. When U.S. 40mm M81 AP penetration is adjusted upward for lower weight, penetration at 2600 fps and 2.375 pounds would be 70mm, still alot less than 2 pounder AP. So U.S. 40mm AP M81 is either much lower nose hardness than 2 pounder, or 40mm is a flat nose projectile.

Does anyone have a drawing of the subject rounds (M81 and M81A1) that would show if they had a flat or blunt nose. A friend who was stationed at Fort Drum in Watertown NY told me that anti-aircraft rounds would sometimes have flat nose, which were designed to be extra effective against thin skin targets. While a pointed nose might blow through the armor, in one side and out the other, a flat nose round would use lots of energy getting though armor and take a big chunk of plate with it, increasing chance of major damage and injuries. Military folks referred to flat nose anti-aircraft rounds as "wad cutters" because they blew fairly large pieces of armor into the aircraft instead of cutting nice neat holes with petal shaped fold back edges. Flat nose rounds also limited the range of the projectile, which could prevent practice rounds going off a base and striking houses and cars. Thanks for any help that can be provided.

Based on U.S. tests of Russian APBC against sloped armor, 76.2mm APBC against T34 glacis (45mm at 60° slope from vertical) would be resisted by 90mm vertical plate equivalence. If T34 armor is high hardness, modifier would reduce vertical resistance to 68mm at 0°. This suggests that T34 gun firing Russian APBC could penetrate T34 glacis at 875m. If this is correct, Germans could have ended T34 problem by enlisting captured T34 as T34 tank destroyers. However, if the slope effects for flat nose APBC are influenced by armor hardness (high hardness or face-hardened), than penetration range for T34 against T34 would be reduced significantly. There may be a report where T34 gun was fired at T34 to determine resistance, and this would be very valuable to review.

Russian APBC has very low slope effects at high angles, which has been discussed in previous posts. When 76.2 APBC hits 40mm at 60° resistance is same as 70mm vertical plate, when U.S. 76.2mm hits 40mm at 60° resistance is same as 105mm vertical. The slope effect difference is due to flat nose digging into armor and helping to turn projectile into armor plate, instead of ricochet effect that occurs when pointed or rounded noses strike at an angle. The potential problem in wargame application of APBC slope effects is that the data is based on softish homogeneous armor (250-300 Brinell Hardness), and most German tank targets for Russian guns will have face-hardened armor where hardness may be over 550 Brinell. There is no published Russian penetration data for face-hardened armor at 0° and other angles, based on our research (available data is for homogeneous armor, while face-hardened armor has hard thin surface layer and softer body of armor). So Russian penetration data may not address resistance of PzKpfw III, IV and Panther armor due to face-hardening. And slope effects for Russian APBC against face-hardened armor may be greater than homogeneous tests, since projectile does not dig in as much on face-hardened prior to failure of armor or projectile. Homogeneous armor defeats hits by allowing round to drive into armor and push plate material around, which uses up energy. Face-hardened armor attempts to break up and shatter projectile before round breaks through hard surface layer. Face-hardened panzer armor appears to be one of the main issues that face CM2.

One of the issues regarding published Russian penetration data is the success criteria that was used. Russian tests could use 20% success criteria (20% of hits result in successful penetration), 50% or 80% success. Germans use 50%, like Americans, most of time. British data generally based on 50% for larger ammo, but some 80% may slip in occasionally. Using Russian data that does not have the success criteria spelled out is subject to possible variations. The Russian Battlefield published two types of penetration data, tests at 20% and 80% success criteria and calculations. The calculations ("tabular" data) may not be as reliable as tests, since we don't know the equations used or the assumptions. Since we have tests for Russian APBC against American plate (50% success criteria), our book presents consistent penetration estimates for all Russian APBC, which we compared to data on The Russian Battlefield. Much of the data on that site is very close to our figures, with notable exceptions. Americans estimated that 122mm APBC would lose velocity faster with range than Russians did, is one example of a difference. Russian Battlefield penetration for uncapped AP is lower than our estimates based on nose hardness differences from U.S. AP. About 13% lower, using DeMarre estimate with nose hardness modifier. Our book presents our estimates for Russian penetration and compares result to Russian Battlefield figures. Book also presents estimates based on British test of 76.2 APBC against vertical plate at 610 m/s, which we compared to our estimate and Russian Battlefield data.

Regarding the use of DeMarre style analysis, we have U.S. penetration tests for German and Russian ammo against American test plate, and U.S. ammo against the same test plate. Why bother with DeMarre analysis when data is available for a common basis comparison. There is also the issue of how do nose hardness variations change DeMarre estimate penetration? U.S. penetration tests with 20mm AP at various nose hardness actually underestimate German advantage over U.S. by about 5% when one applies nose hardness factors from 20mm AP tests. Could be 20mm data does not directly scale up to 75mm rounds, or nose hardness is only one factor in a complex picture (impact resistance could be another). Problems with DeMarre estimates for varying nose shape and nose hardness rounds is why British tested U.S. 76mm APCBC, German 75mm APCBC, 17 pounder APCBC and Russian APBC at 610 m/s against vertical plate. Russian APBC does not follow DeMarre analysis, because penetration for flat nose projectile does not vary with velocity^1.428 power, it varies by different factors within certain velocity ranges. We only use DeMarre type equations when there is a need to estimate data for which there is no published figure or a particular figure looks funny (too high or low). American APCBC does not penetrate as much as German at same velocity, weight and diameter due to nose hardness differences and other factors. British tests at 610 m/s showed this, 103 for German 75mm and 90 for U.S. 76mm. Sherman 75mm APCBC would penetrate 89mm at 610 m/s when DeMarre estimate is made from 76mm penetration in test. CM has much higher homogeneous penetration for Sherman 75mm APCBC, about 98mm at 610 m/s versus 89mm in British and American tests.

Could some provide the web site address where the Canadian tanker talks about Panther kills through mantlet ricochets and estimates the size of the area he had to hit. Thanks.

Based on the area that has to be hit to ricochet a round down on the Panther hull top, what is the overall probability of doing the job? What is the total area in terms of meters squared or feet squared? I think the Canadian expert at ricochet Panther kills defined the size but I don't have the web site address anymore, could someone post it on this thread. Thanks.

Giving high rate of fire guns the same effectiveness against tank weak spots was one of the joys of the TRACTICS ruleset decades ago. A machine gun, quad .50 cal halftrack or 20mm auto cannon would plaster a King Tiger with hits and some would end up going down the 88 barrel and doing all sorts of damage, or would find their way through a vision opening, or down the hull machine gun barrel, or between two armor plates, etc. High rate of fire is usually associated with smaller rounds, and small ammo is more impacted by all sorts of things than 75mm projectiles. Slope effects for 37mm APCBC are head and shoulders higher than 57mm APCBC through 90mm APCBC, so it would be reasonable to assume that when 37mm hits 100mm cast mantlet at a high angle the nose gets bent more than 75mm round. A bent nose would seem to result in more chance of awkward flight angles down towards the Panther hull top, where the nose impact angle on armor is different from the projectile direction. High rate of fire comes with some features that are bound to decrease the effectiveness.

The only thing that might impact a 37mm round and not apply to 75mm hits is what happens when the round ricochets off the rounded mantlet underside. 37mm ammo is long and thin, compared to 75mm, and probably would bend and fly off at an odd angle. Meaning much less penetration when it hits the hull top, maybe even too little to penetrate. No one has a model to predict percentage of mantlet ricochets that defeat the Panther, since data and theoretical stuff is in short supply. It might be that 37mm rounds would not ricochet down from the mantlet and penetrate the hull top, due to bending and distortion as they bounce. 75mm ammo has much higher bending resistance and stronger nose. There are reports of 75mm kills on Panther via mantlet ricochet, anyone ever read of a Stuart getting such a penetration? Regarding weak spots on Panther hull, first M10 combats against Panther in France only resulted in frontal penetrations against tank via ricochet from mantlet bottom, and hits on MG ball that drove it into tank and set Panther on fire. No M10 penetrations of any other frontal armor, including the mantlet itself.

John, The data you posted for Russian gun penetration appears to use German made ammo for the German tests (7.6 kg weight for projectile), and Russian APBC for Russian tests (6.3 or 6.5 kg projectile).

The 76.2mm gun in T34 could penetrate 75mm at 0° and 66mm at 30° at 500m with APBC flat nose ammo. BR-350B ammo. Note that the 30° slope effect is 75mm/66mm, or 1.14. This is less than the thickness/cosine(angle) and is due to the superior penetration of sloped armor by rounds that dig into the armor. Instead of ricochet forces on the nose that push upwards and raise slope effects, flat noses tend to turn the projectile into the armor when the noses bite in. When German 75mm hits 66mm at 30°, the slope effect is 1.23, for Russian APBC it is 1.14. The differences at 60° are even greater. When German 75mm hits 40mm at 60°, the armor resists like a 106mm vertical plate. Against Russian 76.2mm APBC, 40mm at 60° resists like a 70mm vertical. Russian flat nose APBC is wonderful against sloped armor and not so good against vertical armor unless the velocity is very high (over 2200 fps or 670 m/s).