rexford
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Posts posted by rexford
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The total weight of shrapnel is a non-factor, the payoff is in pieces and their velocity. Here is an extreme case that illustrates the point.
A 15# HE shell with small HE detonates on the ground and breaks into two low velocity pieces. There is less than a 50% chance that folks at 5' will be hit, and even then the fragments may not be able to pierce coats and skin (low speed).
Compare to a 5# HE shell that puts out 300 high speed pieces that have enough speed to pierce infantry clothing and skin.
15# of shrapnel has no meaning if it is too slow, and does not cover sufficient area, to yield a high injury probability.
Higher TNT in 75mm means alot of high velocity small pieces, small TNT in 76mm means fewer and larger pieces that often lack the speed to do anything worthwhile.
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Hunnicutt says Brits took out HE burster and put an "inert filler" in the round, could be sand with same weight as HE. Hunnicutt says resulting projectile had same ballistics as original, suggesting it wasn't filled with metal cause that would increase the weight, lower the muzzle velocity an change the flight path so the gun sight wouldn't match the projectile any more.
APCBC with an HE burster loses penetration because the HE burster opening weakens the projectile structure so that it absorbs impact energy during hits, which lowers penetration compared to solid shot.
If we assume that Brits used sand filler to maintain same exact weight, then 75mmL40 APCBC penetrates the same whether Brit or U.S. and we continue to ask why CM for 75mm APCBC is about +10% above U.S. penetration data when 76mm APCBC is about -8% below U.S. data. Both rounds were similar in size and construction.
Based on our analysis of German data in another message, the physics model appears to lower penetration as velocity increases and the model may give bonus' to low velocities.
One reason Brits were afraid of HE bursters is cause spaced armor on PzKfpw III caused round to detonate inbetween spaced armor and main plate, defeating round.
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While 76mm HE would have a bit more total weight shrapnel than 75mm HE (thicker walls and bigger round), it is the number of pieces and their velocity that does damage, not the total weight.
If one round has 15 lbs of shrapnel but 3 pieces due to a little explosion, and a 7 lb round puts out 500 pieces with effective velocity (sufficient velo to penetrate clothing and get through skin), which is more effective at 2' range?
Having twice the weight of shrapnel but only two pieces means the chance of hitting someone standing right next to the blast is less than 50%!
The bigger the explosion the more little pieces and the higher the velocity of the pieces, and the higher the probability of hitting someone and doing something.
Fragments and velocity is the key factor, pounds of shrapnel is almost a non-issue if the velocity and number isn't there.
We believe that the U.S. HE data is based on tank gun shots at the ground at some range that isn't listed on our pages. The blast area heavily sways to one side, suggesting it is a gun shot.
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It is possible in the game, but the question is whether it could occur in real life with 37mm.
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The equation for max trajectory height versus flight time matches actual data to within 0.1m, it has been checked against detailed German data and a sophisticated naval ballistic program in BASIC language. It is considered adequate for hit/miss estimation due to the small errors that result.
The trajectory height is taken above the line from gun barrel to target aim point, the dispersion is measured from the trajectory curve height.
If a Tiger is using battlesight aim and aims at the hull bottom on a T34, the trajectory height is taken from gun barrel to hull bottom.
Since most shots are at a good range, it might be okay to assume that the gun barrel is at the same elevation as the target point on the target, on level ground. This will be checked into.
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The DeMarre equation has been around a long time, and is generally accepted as a reasonable way to estimate the penetration of rounds at different velocity to predict an unknown projectile penetration from a known penetration for a different size round of the same type and country.
Projectiles must be reasonably consistent in national origin, construction and manufacture for DeMarre estimation, but exact consistency is not required.
In the past we have used the DeMarre equation successfully with American, British and Russian projectiles, and DeMarre should apply to German ammo.
Using CM data for the 75mmL48 as a basis we DeMarre estimated 0m/0° penetration for 75L70, 88L56 and 88L71 and compared results with CM listing:
75L48 (750 m/s)
144mm CM and DeMarre basis
75L46 Pak 40 (793 m/s)
144mm CM
156mm DeMarre
75L70 (935 m/s)
178mm CM
198mm DeMarre (194mm if 925 m/s)
88L56 (780 m/s)
159mm CM
169mm DeMarre
88L71 (1000 m/s)
224mm CM
244mm DeMarre
Since the penetration fall-off in CM with range appears to follow the standard DeMarre equation relationship:
penetration proportional to velocity raised to 1.4283 power,
the penetration estimates in CM for 75L46, 75L70, 88L56 and 88L71 may require re-examination since they appear to be low if the 75L48 penetration is correct.
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How does one download patches and where are they found.
All of this escapes me.
Thanks for help.
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HE tests from tank guns would probably strike at a small angle from ground level, like a few mils (thousands of a degree), and probably wouldn't bury themselves in the ground.
If a Sherman is 100m from infantry cowering in the brush and fires HE at them, the angle from gun to ground impact is maybe 1° above horizon. Burying seems a remote possibility.
HE effectiveness, after considering all thoughts in the spread, should be a function of target status.
1. Need to shoot HE through a bunker opening, hit a stone wall or knock infantry off a StuG III, got to have velocity and a flatter trajectory so U.S. 76 HE gets more FP than 75mm HE
2. Going after infantry in the open or in vegetation (including trees), 75 gets the call
3. Need to blow something up with blast, collapse a sandbag MG nest or intimidate with alot of noise so people keep their heads down, bring on the 105 and forget about the 75-vs-76 controversy
As an aside, Australian infantry in Nord Afrika found an innovative way to reduce sandbag MG emplacements when artillery could not be there. They used anti-tank rifles to knock over the bags, one by one.
Did not look at relative armor penetration between 75 and 76 HE, will do today after work.
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When Tiger I side armor was hit by 6 pounders and other guns in test firings, it acted like 240 BHN U.S. test plate. It takes very large hardness figures to change projectile penetration. Even 350 BHN Tiger I side armor seemed to act like 240 BHN U.S. test plate.
The 0.85 modifier you use for Sherman flawed armor converts the resistance to U.S. 240 BHN high quality test plate. I have read the back-up on this and saw the graph.
Firing tests during WW II suggest that German armor (homogeneous) may be harder than 240 BHN, but in the final analysis it resists like U.S. test plate at 240 BHN.
The harder the plate made by Germans, the greater the chance for bad things in there.
U.S. 75mm APCBC penetration with HE burster would be about equal to U.S data after adjustments, 76mm APCBC penetration by CM is about 8% higher than U.S. data. 37mm APCBC in CM is about 20% lower than U.S.
Why would U.S. 75mm with HE burster in CM perform consistent with U.S. data and 76mm be sub-par. This suggests that the physics model may need tweaking: the key to successful models is whether they are consistent with firing tests, it would seem that U.S. 75mm and 76mm should either both agree or both disagree with U.S. test data.
When 37mm hits 30mm face-hardened side plates on PzKpfw IVH, or 40mm face-hardened on Panther A side, it would not lose 20% of U.S. test penetration due to hardness. It would seem that German face-hardened would be equal or inferior to U.S. test material, not better.
When 37mm APCBC hits 300 BHN Panther or PzKpfw IVH turret side, a 20% reduction from 240 BHN penetration seems like too great a penalty. 37 APCBC is not about to penetrate 80mm plates at 350 BHN on Tiger I, and will mostly kill 40mm, 45mm and 50mm thick armor where BHN effects should be minimal.
37mm face-hardened and homogeneous penetration is about equal in U.S. tests.
There may also be a need to differentiate between U.S. and British 75 APCBC based on previous messages by others, due to penetration reduction associated with HE burster which may be about 8% to 10%.
(did British change all 75mm APCBC rounds used in their Shermans or did they use some American made rounds "as is" : it would seem that British industry might have other, more pressing matters than removing HE bursters from 75mm rounds and inserting metal filler)
We're not Stuart tank fanatics, although maybe a little fixated on the sanctity of U.S. test data and insanely driven with regard to a possible re-examination of 37mm data.
If a model is going to adjust U.S. data and is based on good reasoning, that is your choice and lawful right as game designer. We would not try to force any data on anyone.
We're just suggesting that the model might be improved by assuring that it is consistent in the manner that it treats U.S. 75mm and 76mm penetration after comparing model results with test firing data.
If 76mm performance is reduced, 75mm performance with and without HE burster should be reduced from U.S. test data. The rounds are too much alike to seem to warrant different model results.
Thanks for your patience on this thread.
P.S.
We view an 8% to 10% difference in penetration data as something meaningful. For 76mm APCBC, we're talking about a 500m change in penetration range on alot of shots. For 37mm APCBC, a 10% change in penetration (if CM data were only 10% different from U.S. instead of 20%) is associated with a 250m range shift.
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The physics model may be based on the British NPL equations which are limited to British plate characteristics and projectiles.
We have the NPL reports, British plate fell completely apart when it exceeded 400 BHN and rounds overmatched it at 40°, high hardness armor built by the Russians and Germans did not react as badly.
British armor plate did not harden adequately if it was thicker than 2.5", and 152mm was equivalent to about 139mm of U.S. armor. This is the stuff that may have been used in the NPL tests.
If 37mm APCBC penetrates 79mm of good quality U.S. test plate at 0m and 0°, what will it do against inconsistent German armor plate from an alloy starved industry that is being bombed on a regular basis and is using a complicated heat treating process prone to errors when one step is held for an extra second or two.
37mm APCBC is predicted in CM to penetrate less German armor plate (homogeneous and face-hardened) then it can do in a U.S. test against good test plate. British and U.S. test firing against German 30mm face-hardened plates in Afrika showed that the plate could vary in quality, usually lower than U.S. material and almost never better.
While everyone's data can't be taken at face value, we know so much about U.S. penetration data (TM-9-1907 and other publications) that is would seem logical to use the stuff and try to convert everything else to that standard.
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I put a detailed explanation of the spreadsheet on the tanknet site, in response to the inquiry from Conall.
The Peng stuff is never opened by me because it is obvious where it is headed, and we don't want to go there. Others can simply avoid our road.
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Robert Livingston did some measurements on a real M4A1, and it is alot more vulnerable than other Shermans with 55°/56° glacis angles.
The center portion of the glacis has 51mm at 52°, 53° and 55°, and the large driver hood is 64mm at only 35°. In addition, M4A1 front hull armor is all cast, which could lower the 85% quality modifier even further (the 85% quality appears to apply to rolled armor with flaws, and cast is less resistant than rolled).
While 56° glacis Shermans with rolled and cast armor put extra plates over the driver and MG hoods to bolster very weak areas, it was not done on the M4A1.
As noted by Robert in his AFV NEWS report, M4A1's were viewed as so easy to penetrate that 743rd Bn tankers kept them out of combat.
M4A1's may have curved surfaces that will occasionally cause a bounce, but the weak areas are right in the middle and would seem to make the tank inferior to other Shermans.
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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.
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Since physics models can't catch all the factors, one would think that test firings might be more accurate, and that physics model validity would be checked by seeing if it duplicated test results.
If 37mm APCBC penetrates 79mm of armor in a firing test against real armor, and a physics model predicts 63mm, which is better or more dependable?
The British took PzKpfw III's in the desert and shot 37mm, 40mm, 57mm and 75mm guns at them, and the penetration ranges agreed very well with predicted ranges from penetration test data.
Since Panther A and D have face-hardened armor hull side armor, did the physics model also predict face-hardened penetration. British tests in North Africa showed that allied penetration tests against face-hardened armor worked really well in the field for range prediction.
And DeMarre estimates for 2 pounder AP penetration against face-hardened armor from U.S. 57mm AP matched penetration ranges against 30mm face-hardened German armor.
If CM penetration data for 75mm APCBC were decreased by 9% for an HE burster, the figures appear to closely match U.S. test data closely. Why would 37mm APCBC vary by so much between CM and U.S. data if 75mm APCBC-HE appears to match?
The British tests for 6 pdr AP penetration against the side of a Tiger seemed to agree very well with test data. Using penetration estimates 20% below test data for 37mm APCBC just seems like a drastic move when the data has not been shown to perform in an unacceptable manner, and U.S. 75mm data appears to match test firing results.
It would be interesting to learn more about the physics model, which might put alot of questions to rest.
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U.S. TM 9-1907 lists following penetration for 37mm APCBC solid shot at 0°:
100m-77mm
500m-68mm
1000m-58mm
1500m-50mm
2000m-43mm
This is quite a bit different than CM listing. The 75mm APCBC is high and the 37mm is low.
Below is TM-9-1907 for 76mm APCBC:
100m-131mm
500m-119mm
1000m-106mm
1500m-95mm
2000m-84mm
2500m-75mm
This is much higher than CM listing.
Since penetration probability is sensitive to penetration/effective armor ratio, 10% difference in penetration figures can mean a big difference.
As an aside, have played several homemade scenario's with CM and the game flows really well, with slow times between shots and movement.
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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.
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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%.
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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.
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Data from same source as that used in 76mm inferiority study shows following probability of hitting 6 square foot target with effective fragments:
10'-76%
20'-13%
30'-3.9%
40'-1.6%
50'-0.76%
60'-0.41%
70'-0.23%
80'-0.14%
90'-0.09%
100'-0.06%
Had always thought that standing 20' from a grenade explosion would be more dangerous, will have to play my Nintendo 64 GoldenEye some more to see how they model grenades.
Grenade throws out 158 effective fragments at 10' with initial velocity of 1800 f/s.
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Filling the HE burster in 75 APCBC adds about 10% to the penetration. U.S. data for HE burster 75mm shows 91mm at 0m, 82mm at 500m.
A 10% increase can be alot.
Does CM have 50% penetration when penetration exactly equals armor resistance?
If CM does use the navy ballistic limit for penetration, than a 10% increase in penetration raises a 50% probability penetration (pen.=armor resistance) to almost 100% success.
The difference between 82mm and 89mm can make a difference on Tiger and Panther side hits at an angle, inside 500m range.
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For first shot HE at infantry in low brush woods, 75 HE will cause 30% more casualties than 76mm, based on our calculations.
The 75mm advantage is based on these factors:
1. More fragments and higher velocity pieces
2. Lower HE velocity than 76mm, which means less ground scatter
German data shows that flatter trajectories have longer ground scatter along the firing line, since random up-and-down dispersal effects flat trajectories more.
On follow-up shots, the 75mm HE advantage should increase.
Thanks Conall for tracking down the Jurens article. The article listed the BASIC program steps but Mr. Jurens provided a 5 1/4" floppy with the program, which I still have.
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37mm kills due to Panther mantlet ricochets is an issue that would be best addressed by some sort of historical support or report. Maybe some Panther crewmen who have knowledge of mantlet ricochet problems could speak on the limitations of the problem (which ammo types were of practical concern).
Would heavy machine gun AP bullets at 100m ricochet and kill a Panther?
We know that ricochet kills occurred but there really isn't a large database with ranges and what type of ammo and range.
37mm APCBC ricochet kills seem far-fetched, long thin 37mm rounds would probably bend and fly off at a weird angle.
37mm ROF adds to the problem.
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Rounds with caps will have less penetration at close range than uncapped AP, because caps absorb energy as they collapse.
Does American ammo penetration for Sherman 75mm vary from British?
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If plate thicknesses are equal, plate at 60°from vertical resists hits better than 45°, and that explains why one case penetrates and the other bounces after digging in for awhile.
Armor resistance determines if hit goes through or flies off.
M4A1 FRONT HULL ARMOR
in Combat Mission Archive #3 (2001)
Posted
Cast armor has less impact resistance because rolling change structure. Cast armor has less penetration resistance than rolled, cast 2" hit by 75mm has -14% less penetration resistance than 2" rolled.
Looking at the front hull of the M4A1, it has a large % of area that would deflect alot of hits due to vertical and lateral angles.
A smaller defeatable area may compensate to a degree for weaker armor. Good point about welded armor, although later 56° glacis Shermans may have had few glacis pieces.