37mm APCBC PENETRATION

[rexford]

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.

[Slapdragon]

CM does not use penetration tables but a physics model that is more accurate than an abstracted table in most cases. Thus no CM pen figure will exactly match a tech manual or even a test firing -- it is trying to simulate condition in actually field firing.

[rexford]

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.

[John Hough]

Part of the problem has to do with the nature of the tests, done under different conditions, with different test plates, at different angles, and with different definitions of penetrations in each country, when cm has to provide numbers based on a consistent standard for everybody's guns.

CM's physics model is based on some post-war british paper, modified, based on someone else's research, because the original had problems with different angles. A search will probably turn up too much information, but I seem to recall there was a thread about the King Tiger's gun with a lot of good info in it. Try searching for 88L71 and physics model, that might get you what you're looking for.

-John

------------------

sometimes i'd like to kick your f-ing head

but i guess you're just a human too

-EMBRACE, "SAID GUN"

[rexford]

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.

[Guest Big Time Software]

Another problem with test firing data is that the Brinnell hardness rating of the target test plate varies from one to the next and even more so from country to country. This has a considerable effect on the results.

The penetration values printed on-screen in Combat Mission are for attacks versus 'typical' enemy plate hardnesses at the given thicknesses. So for this reason (among others) they may differ from published test results which are against 'friendly' (test) plate.

Combat Mission models Brinnell hardness of armor, BTW, along with face-hardened vs. homogenous. The penetration numbers you see on screen are 'typical' ones, not the only ones used in the game. We determine penetration using formulae, not tables.

Also, CM models the problems with late-war German armor (poor alloys, etc.) by downgrading many German vehicles with percentage-quality ratings below 100%, some as low as 85%. The Panther is rated at 85% in CM, meaning that its armor is treated as if it resists only at 85% of expected strength.

Charles

[This message has been edited by Big Time Software (edited 01-08-2001).]

[hnh3_cm]

anti-spam bump

[rexford]

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.

[illo]

Is 85% armor quality to panther and 95% to sherman realistic? Should there be variation in numbers. I guess not all Panthers were made of lowest quality armor.