rexford

Our estimates are based on a penetration-vs-velocity model that seems to have worked for 45mm, 85mm, 100mm and 152mm APBC data from Russian sources. As suggested in my previous response to the above comments, random variations can enter into penetration tests and make the results look much different than the true average. Without a math model to compare results to, those random fluctuations might not be given the proper consideration. Have you normalized the penetration-vs-velocity data from the tests you have using regression analysis? That would help reduce the impact of random variations. [ November 13, 2002, 05:36 AM: Message edited by: rexford ]

One of the big concerns is that CMBB may not penalize tanks that have large amounts of turret side armor visible from the front, where ricochets would occur on hits due to angle. Gun scatter enters the picture with regard to how often that flat area gets hit. Tiger 88mm APCBC pretty much travels in a straight line horizontally with little side to side movement, 75L43 APCBC scatters much more. At 800m, 68% of Tiger 88mm rounds are within 5" of the aim point, left or right. Or within 0.128m. At the same range, 68% of 75L43 shots are within 11.5" of aim point, left or right. Or within 0.293m. Throw in some errors for out of alignment scopes and gunner errors and many shots will still be closely lined up laterally with aim point. So hits will tend to bunch laterally around the aim point, which is the center of the turret width when the turret is pointing straight at the gun. Turret center and lower sections are hit more often than outer width and upper sections when aim point is center of mass (on glacis). That flat area is in a choice location for hits. In our miniatures games, which plot shot location against the aim point on a model, the flat area on the T34 turret mantlet gets hit alot.

CMBB may include a cast armor deficiency factor that was not in CMBO. IS-2 turret front and mantlet may suffer from some high hardness factors as well as quality decreases. CMBB introduces many factors that change armor resistance quite a bit. 100mm cast Panther mantlet loses 6% of resistance against hits compared to rolled armor, just because it is cast.

Turret front on T34 M41 has this big flat area just below the gun which is 45mm thick. See pictures and drawings on following site: http://www.battlefield.ru/t34_76_2.html So the armor is not really well rounded but contains a nice fat flat area. Panther 100mm cast mantlet is fully rounded. 100mm cast resists 85mm hits like 94mm of rolled armor (rolling armor introduces structure changes which toughen the steel, castings are not rolled). Assume Panther mantlet is rounded with 70 arc above and below apex or center point, and calculate vertical resistance against 85mm APBC: ---------------------------------------------- 18% strike at 10° or less, resistance is 98mm vertical ---------------------------------------------- 18% strike at 11° to 20°, resistance varies from 98mm to 102mm 36% strike armor that resists like 102mm or less when hit by 85mm APBC ----------------------------------------------- 17% strike at 21° through 30°, resistance is 102mm through 109mm ----------------------------------------------- 15% land at 31° through 40°, resistance is 110mm thru 126mm. ------------------------------------------------- If 85mm penetration is 104mm at 1000m, just under half hit Panther mantlet with enough to usually get through if turret is pointing straight at gun. Introduce an angle from turret front to gun and armor gets a little better. Key here is APBC slope effect. When 88mm APCBC hits 94mm at 30 degrees angle, vertical resistance is 116mm, when 85mm APBC hits same armor resistance is 109mm. APBC flat nose digs into armor, reduces or eliminates ricochet forces, and promotes penetration (although APBC is much softer than German APCBC so penetration difference is not as large as it could be). Panther 100mm mantlet is curved but good percentage of hits land near center where angle is not that large, and 85mm APBC has superior slope effects which reduce impact of angle on penetration capability.

Forgot to add in previous post that our 45mm L46 APBC penetration estimates, which were based on a calculation from 122mm APBC, matched up well with a 1940 Russian test. So many of our data points for a wide spectrum of gun sizes are in close agreement with published Russian figures. As I noted on Tankers forum, Russian 76.2mm APBC penetration data has a 7% standard deviation, so the average penetration from a single data point could be more than 7% from the true average 32% of the time. Have you considered that? An 8% difference could result from random fluctuations in ammo and plate resistance. Please publish the 0 degree penetration figures for 76.2mm APBC that you have, including the muzzle or striking velocity and the source, as long as we are putting our data out into the open. Or at least advise if the figures in our book on page 59 (80mm at 250m and 75mm at 500m, at 0 degrees) appear high or low. That would allow us to discuss your figures in a logical way. For 76.2mm BR-350B APBC, we assumed 680 m/s muzzle velocity and the penetration dropped off with velocity according to the equations presented on page 49 in our book. The Russian penetration figures for BR-350B at 0 degrees from 100m to 1000m, as posted by Vasiliy Fofanov, drop off at almost the same rate as our predictions. Russian figures for BR-350B at 0 degrees, ----------------------------------------- 9% drop in penetration at 100m to 500m, 18% drop in penetration from 100m to 1000m Our book estimates, ----------------------------------------- 11% drop from 100m to 500m, 21% drop from 100m to 1000m If actual muzzle velocity is 655 or 662 m/s, this may account for differences over range since penetration is assumed to change as velocity raised to a power. 76.2mm APBC velocity profile we assumed over 0m through 500m range: 100% of muzzle velocity at 0m 98.3% at 100m 96.7% at 200m 95.1% at 300m 93.5% at 400m 91.9% at 500m Here is how we derived the 500m penetration figure for BR-350B APBC from 76.2mm tank gun: A. muzzle velocity is 2230 fps B. 500m velocity is 2230 x .919, or 2049 fps C. 122mm APBC penetration at 2049 fps equals 0.00012434 x (2049)raised to 1.80508 power, or 118mm D. 76.2mm APBC penetration at 500m is 118mm x 76.2/122, or 74mm. Slight difference from book result is due to spreadsheet calculations in chart which used a difference velocity profile over range. As noted earlier, would appreciate seeing something from your data, including how many shots at each range were used to develope points. Fair is fair. I showed you ours, now show me yours.

Thank you for offer. Would like to see the list, at your convenience. The book section you refer to is based on U.S. trials with 122mm APBC, Russian penetration test results during WW II (provided on Russian Battlefield site and by Vasiliy Fofanov), data in Woodman's book and analysis of all the data to see if it made sense and was consistent. Recent posts on Tankers forum show that APBC estimates in our book for 122mm and 85mm rounds are consistent with Russian figures from WW II. Our penetration data was applied to post-WW II Russian trials against captured American armor from Korea and worked fairly well. Firing tests with 100mm APBC captured during 1950's showed rounds penetrating less than we predicted, which could be due to lowered quality export ammo, or could be result of high impact velocity which diminished APBC performance. The 76.2mm T34 APBC estimates we prepared look reasonable but have some troublesome aspects. Our analysis of 57mm APBC penetration data from Russian sources, using all the data we have accumulated, suggested muzzle velocity was 871 m/s instead of the 990 m/s that is usually quoted. Mile Krogfus sent me an American penetration graph for Russian ammo at 30 degrees that listed 57mm L73 APBC muzzle velocity at 850 m/s (interesting, wouldn't you say). While there is always room for improvement, and I am always going back over the Russian penetration figures and comparing them to combat results, our work seems to have many consistencies going for it. Fragile is not the correct word for the Russian penetration estimates, since the results have been tested many times. It may be that further work will change some of the figures. The biggest issue right now concerns Russian AP penetration stats, which limit 100mm and 122mm guns to very short effective ranges against 82mm/55 degree armor. Source references that might help verify what we have done to date, or suggest improvements, would be gratefully accepted. Lorrin [ November 12, 2002, 07:02 AM: Message edited by: rexford ]

Actually, Jeff's statement is not totally correct. When 122mm APBC proved effective against sloped tank armor it appears to have surprised the Russian tank designers. 122mm APBC was not necessarily developed to fight Panthers. However, it is notable that SU 100 was originally intended to use APBC ammo and would have if production problems had not eliminated that option. The Russians appear to have known about the superior sloped armor effectiveness of APBC by the time SU 100 was being designed. I never implied that APBC was developed to penetrate sloped German armor, and don't remember anyone else say something like that on this forum.

Jeff's last statement, about APBC only doing well against overmatched armor, is not correct. Actual firing test results disprove his assertion. 122mm APBC firing tests showed that the round did better and better against really thick armor as the impact velocity increased. The rate of penetration increase for a given increase (%) in velocity improved as impact velocity increased. Above 2200 fps 122mm APBC penetration increases as velocity raised to 2.5 power, from 1800 to 2200 fps penetration increases as velocity raised to 1.8 power. The math disproves Jeff's point. A 10% increase in velocity above 2200 fps buys 27% more penetration, at 2000 fps a 10% velocity increase buys 19% more penetration. 122mm APBC penetrates 207mm at 2600 fps impact, which is the opposite of the condition Jeff referred to. When the impact velocity of flat nose APBC increases, the armor's ability to resist the tremendous impact imparted by the blunt shape appears to radically decrease. There are limits here, such as when 57mm APBC strikes at 3000+ fps. 57mm APBC doesn't do very well for some reason.

The site has some really interesting details and I appreciate your bringing it to our attention. Looking over the gun stats: The penetration data is for tungsten core rounds for most weapons, even if the tungsten round was not available at Kursk (like 76.2mm APCR from T34 or field gun). Data does not cover the majority of ammo, which was APCBC (German), or APBC and AP (Russian). 122mm field gun was supposed to be most effective Russian weapon at Kursk against Tigers, site presents HEAT penetration figure for a gun that fired AP as primary round (122mm HEAT given to SU 122 for self-defense).

Presumably then the APBC had a higher velovity too - 'cos I'd certainly expect a pointed round to have better penetration than a blunt one at that range and angle?? Yep - my point exactly.</font>

Russian APBC has a flat nose and ballistic windscreen to reduce air resistance, AP is pointed nose and uncapped, loses velocity much faster than APBC. 122mm APBC penetrates 207mm at 0m and 0 degrees, 122mm AP defeats 174mm at same range and angle. 122mm APBC is superior against sloped armor since square nose digs in and counters ricochet forces, penetrating 82mm/55 degrees at 1750m. 122mm AP penetrates same armor at 100m. Having a few 122mm APBC for use against Panthers drastically changes things.

Muddying the waters some more, Miles Krogfus just posted on the Yahoo! Tankers site to effect that American and British compilation of Russian 100mm and 122mm ammo found in Berlin was all pointed nose. No APBC found. Currently seeking more details on number of tanks and guns that contributed to ammo finds. Could be a few vehicles where APBC all used up, or wasn't available due to street fighting nature of combat (emphasis on HE). Or 122mm APBC limited use in general and not available to many guns and tanks.

My calculations in the past for 37mm German AP overlooked some factors such as big HE burster cavity and probable use of less than ideal metal quality. Penetration estimates for German 37mm rounds have been downgraded for purposes of our book. Posts on this forum addressed possible 37mm penetration revisions which could be examined by CMBB crew. With revised figures, German 37mm AP doesn't appear to bust through T34 turret front armor as much. We also revised 50mm APC penetration due to bigger than typical HE burster size, and inability of 50L42 on PzKpfw III's to do much against KV-1 75mm side armor. Possibility that 50mm APC penetration needed some downgrading was noted in some posts. German 75mm APCBC and Tiger APCBC had 0.2% of projectile weight as HE burster, which is really small. 37L45 AP has 1.9%, which is ALOT. 50mm APC had 1.2%, I think. 88L56 Flak rounds had 1.65% HE burster during early and middle war years, and metal was not so good based on penetration figures presented in Jentz' DREADED THREAT book. This may have been posted in the past on this forum.

Sherman 75mm AP round outpenetrates APCBC against rolled homogeneous armor, and is not so good against face-hardened. Difference is the caps, and uncapped AP loses velocity much faster than APCBC. 75mm AP Homogen. armor: 109mm at 100m and 84mm at 750m Face-Hard armor:91mm at 100m and 66mm at 750m 75mm APCBC Homogen. armor: 88mm at 100m and 77mm at 750m Face-Hard armor: 102mm at 100m and 90mm at 750m 75mm APCBC does to face-hard what 75mm AP does to homogeneous armor. I think CMBB only lists the homogeneous penetration for a weapon, which might be misleading people. Americans found that uncapped M72 AP for Sherman 75mm gun was shattering ALOT. I believe that Russians found that Sherman 75mm ammo was pretty good against Tiger side armor at close to medium range. 75mm AP looks like it would eat up Tigers frontally and from side at close and medium range, but it shatters and has other problems.

Could you give us a link?[/QB]</font>

Eh? I always thought that, other things being equal, capped shot performed better at high angles of impact and uncapped at near normal. Of course, other things aren't equal here, because of the FH plate. All the best, John.</font>

What is the penetration of the 122mm AP compared to the APBC. It now seems certain according to Svirin that the APBC was never actually used in front line combat apart from field trials and rare tests. Heereswaffenamt august 1944 tests with JSII 122mm AP v Panther glacis, show it couldn't penetrate it at point blank range.</font>

What is the penetration of the 122mm AP compared to the APBC. It now seems certain according to Svirin that the APBC was never actually used in front line combat apart from field trials and rare tests. Heereswaffenamt august 1944 tests with JSII 122mm AP v Panther glacis, show it couldn't penetrate it at point blank range.</font>

Latest thoughts on subject is that 122mm APBC became available in limited quantities starting January 1945, and that 122mm AP was primary round through end of war. I believe that CMBB makes 122mm APBC the only armor piercing round starting August 1944, which may overstate effectiveness of 122mm ammunition.

The width of Russian tank mantlets is generally narrow, but so is the lateral dispersion of certain German ammunition: 88L56 APCBC 500m 68% of lateral scatter within 0.11m of aim point 1000m 68% within 0.16m of aim point 1500m 68% within 0.23m of aim point ---------------------------------------- 75L48 APCBC 500m 68% within 0.17m of aim point 1000m 68% within 0.40m of aim point 1500m 68% within 0.68m of aim point ------------------------------------ 88L71 APCBC 500m 68% within 0.12m of aim point 1000m 68% within 0.21m of aim point 1500m 68% within 0.38m of aim point ---------------------------------------- Above figures based on scatter of shots when aim is fixed, and they come from German WWII documents. Same documents suggest that above figures be doubled for combat results where gun sights may be slightly out of adjustment, gunner is under pressure and does not aim at center of target mass, target center of mass is indistinct, etc. IS-2 turret mantlet and turret front that is curved in one plane to directly facing gun is about 1m wide, or 0.5m to left or right. Call this width the "vulnerable area". At 1000m, Tiger E round that has vertical trajectory landing on IS-2 "vulnerable area" will have almost all of the rounds (88%) scatter laterally within 0.5m of aim point and hit that area (with doubled scatter). At 1000m, 75L48 round with vertical trajectory falling on IS-2 "vulnerable area" have 47% of shots scatter laterally within 0.5m of aim and land on area (with doubled dispersion). Guns like 88L56 not only have good penetration, but possess exceptional scatter characteristics which make a large difference on the battlefield and result in added effectiveness against turret fronts with narrow vulnerable areas. British firing tests with Tiger 88L56 show gun puts shots within a narrow band (when Tiger aims at an ATG or the turret/hull intersection, it has good chance of hitting it). [ November 02, 2002, 07:11 PM: Message edited by: rexford ]

We have German ballistic tables for vertical and lateral scatter based on constant aim. Then one cranks into the scatter spread due to range estimation errors. For the 75L48 against IS-2 front, I assumed 65% chance that vertical scatter will fall within 1m of aim point, and 90% chance that lateral scatter will fall within 1m of aim point. Overall probability of landing shot with 2m x 2m is actually 59%. For our wargames we estimated scatter probabilities for first, second, third and following shots based on ability to put shots within the 2m x 2m box. Separate probabilities for vertical and lateral scatter, since range estimation errors make vertical scatter much larger. If you e-mail me directly and my scanner works I'll send you some of our tables. One table has shot scatter from aim point as a function of scatter probability within 2m x 2m box and dice roll with two decimal dice (1 through 0 on each dice). Interesting thing is that assuming 25% average range estimation error on the first shot and test based lateral scatter grossly overestimates hit probability at close and medium ranges. According to the ballistic model, being 25% off on range at 200m should never miss, however, actual combat results show misses do occur, particularly when gunners are scared, tired or inexperienced. A book I read had a Jagdpanther 88L71 miss a stationary Sherman at close range, the math says this would never happen but a "straight out of gunnery school" novice missed. The bottom line is that people act like people on the battlefield and do not follow ideal statistical trends, which is something BTS has been saying for a long time. P.S. In the Unforgiven, when Clint Eastwood faces off against a room full of "bad guys" at the end, most of them hold their guns out and shoot without taking careful aim. S.L.A. Marshall did studies where about 25% of infantry fired their weapons. Getting people to accurately fire is alot different from what some wargames assume.

Jeff Duquette posted a drawing of 75L24 ammo on the Tankers site and it had an armor piercing cap that was shaped like a ballistic windscreen cap. So the round is APC. Or, even better, as APC/BC, cause the cap has two functions. British rounds that were APC had a square looking armor piercing cap on the nose, and lost velocity like crazy. 75L24 APC has a streamlined cap that functions in two ways, like the earlier post on this thread stated, which is correct. The 75L24 cap protects the nose from shatter by absorbing and spreading the impact forces, and cuts air resistance due to good aerodynamic shape. Alot of authors, myself included, were mislead into believing 75L24 fired APCBC. So don't believe everything that appears in a published book.

88L71 penetrated IS-2 Model 1944 turret front/mantlet/cupola and lower hull nose (127mm at 30 deg). Sounds like bad rolls.

Using shot distribution tables for the case where 75L48 APCBC where gun has 65% chance of hitting a 2m x 2m target, and rolling dice against a 1/72 scale model, following results obtained against IS-2 front which is aimed directly at firing gun: 59% hit probability (274 hits in 464 shot rolls) 17% of hits strike inpenetratable turret side or top armor 57% land on hull 20% hit turret front/mantlet/cupola with impact angle under 43 deg. 16% land on turret front/mantlet/cupola with angle of 30 deg or less 6% strike turret front/mantlet/cupola with impact angle 43 deg or greater Above figures slightly different from calculations due to use of PST 1/72 scale model for dice rolls and measured shot location relative to aim point, which differs from average figures used in computations. So 16% of 75L48 hits that can penetrate 100mm of armor with an impact angle of 30 deg will defeat turret front/mantlet/cupola armor. Since hit probability is about 60% in above case, this means that roughly 10% of the 75L48 shots will penetrate IS-2 front when gun has 60% hit probability and penetration allows shell to defeat 100mm x 30 deg slope effect x 0.90 quality multiplier (about 113mm penetration for 75L48 at 0 deg).

The subject topic has been discussed quite a bit recently, so I did a ballistic analysis for the probability of hitting the turret front/mantlet, and what the resulting impact angle would be. I assumed that 75L48 APCBC is being fired, with a 65% chance of putting a round within a 2m x 2m box. Important results follow: A. 6% of hits land on turret front/mantlet/cupola that is curved in one direction with impact angle of 56 to 90 deg. 6% land with 42 to 56 deg. angle 6% strike at 30 to 42 deg. 6% land at 19 to 30 deg. 6% land at 10 to 19 deg. 6% land at angle below 10 deg. Curved in one direction means that the turret front areas that have vertical and side slopes are assumed to be too resistant for 75L48. This is the edge of the turret front where it starts to curve towards the turret side. B. About 36% of the hits land on the turret front/mantlet and cupola areas that are curved in one direction ("potentially vulnerable"). Turret sides and top that are seen from front view are not vulnerable for analysis purposes. Although the "potentially vulnerable" turret area/cupola is only 18% of total turret/hull area, about 36% of hits land in the "potentially vulnerable" area. This is due to way that shots are distributed. Most of the scatter is vertical and the mantlet/turret front is close to the aim point where a high percentage of shots land, and the narrow width of hittable turret front is a very insignificant factor. C. If cupola and turret front/mantlet are 100mm thick, and range is such that 75L48 needs a hit within 30 deg. impact to have a chance to penetrate, 18% of the hits would hit armor with resistance equal to or less than penetration when target armor is facing directly at firing weapon. Boring technickel Deetales follow: D. The turret front/cupola area equals 17.2 square feet. Hull front area is 37.5 square feet (area below hull bottom is assumed to be blocked by earth banks) However, potential penetrating hits are limited to cupola and a 3.2' width of turret front which includes the mantlet (eliminates turret front where it is curved in two directions). Turret front/cupola area that might be penetrated ("potentially vulnerable") is 8.6 square feet. Turret front/mantlet and cupola that might be penetrated is about 18% of total area. E. 65% of shots hit tank when aim is at intersection of turret and hull (common German practice that simplifies estimates). 29% of shots hit turret/mantlet/cupola, 36% hit hull front. F. 30% of hits strike turret front/mantlet that is curved in vertical plane ("potentially vulnerable"), and 6% hit cupola. This is close to one-third factor that CMBB supposedly uses for chance that turret will be hit. [ October 31, 2002, 01:20 PM: Message edited by: rexford ]