122mm APBC Availability

[Jeff Duquette]

Lorrin:

Actually your BR-350B data does not match up well, nor does your recent alternate data help. While the front end of your most recent set of figures looks ok -- i.e. 0m to 250m – correlation between your estimates and actual drops with range. This may represent an error in your velocity decay assumptions. What are you using for velocity relative to range?

Or the error may be resulting from something else. Are you using a ratio based upon another known projectiles penetration data to back out the BR-350B penetration data? Or are you using slope effects from 30-degree figures to back out 0-deg obliquity figures. Would you post a sample calculation and derivation? I can’t disscuss this with you in a logical manner if I don’t know how you are arriving at your penetration figures.

Regards

Jeff Duquette

[Ari Maenpaa]

Originally posted by Rex_Bellator:

I have seen the numbers on the data page, and my gut feeling is that the 'Rounded' bonus is not working.

Yes indeed, the 'Rounded' or 'Curved' bonus in CMBB seems to be notably smaller than it was in CMBO. In case it works at all. Perhaps that's intentional and historical, I don't know.

For example the T-34/85 is repeatedly able to knock out Panthers from 1000 meters with hits on frontal turret where the armor is 100mm/curved. The 85's penetration on that range is 104 mm, so it seems like the curved armor surface can't affect the penetration power at all. As an additional detail it can be noted that the 100 mm armor isn't overmatched by the shot's caliber which is 85 mm only. Also the IS-2's curved turret armor is quite a soft spot too.

Could it be a bug in the game mechanics?

Ari

[rexford]

Originally posted by Jeff Duquette:

Lorrin:

Actually your BR-350B data does not match up well, nor does your recent alternate data help. While the front end of your most recent set of figures looks ok -- i.e. 0m to 250m – correlation between your estimates and actual drops with range. This may represent an error in your velocity decay assumptions. What are you using for velocity relative to range?

Or the error may be resulting from something else. Are you using a ratio based upon another known projectiles penetration data to back out the BR-350B penetration data? Or are you using slope effects from 30-degree figures to back out 0-deg obliquity figures. Would you post a sample calculation and derivation? I can’t disscuss this with you in a logical manner if I don’t know how you are arriving at your penetration figures.

Regards

Jeff Duquette

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.

[rexford]

Originally posted by Rex_Bellator:

Hi Rexford,

I don't want to sideline your interesting thread, but as the most knowledgable fellow around , can you please spare one post to help me with something which is bugging me with the T-34M41 series.

Dou you think it is reasonable that according to the armour thickness colour bars around the T34 picture in the toolbar, the weakest armour on the whole tank is on the front turret? It would seem that the T-34 is an awful design if they put the weakest point at the most likely place to be hit.

I have seen the numbers on the data page, and my gut feeling is that the 'Rounded' bonus is not working. I know the penetration capability of various smaller German AP rounds is being tweaked in a patch, but I wonder if they have approached the problem from the wrong end.

Many thanks

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:

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18% strike at 10° or less, resistance is 98mm vertical

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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

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17% strike at 21° through 30°, resistance is 102mm through 109mm

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15% land at 31° through 40°, resistance is 110mm thru 126mm.

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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.

[rexford]

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.

[Guest Mike]

Originally posted by rexford:

</font><blockquote>quote:</font><hr />Originally posted by Rex_Bellator:

Dou you think it is reasonable that according to the armour thickness colour bars around the T34 picture in the toolbar, the weakest armour on the whole tank is on the front turret? It would seem that the T-34 is an awful design if they put the weakest point at the most likely place to be hit.

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.

</font>

[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.

[rexford]

Originally posted by Jeff Duquette:

Lorrin:

Actually your BR-350B data does not match up well, nor does your recent alternate data help. While the front end of your most recent set of figures looks ok -- i.e. 0m to 250m – correlation between your estimates and actual drops with range. Regards

Jeff Duquette

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 ]

[Ari Maenpaa]

Thank You for the very detailed reply Rexford.

It indeed seems that the cast defiency has been modelled in CMBB as an elite T-34/85 was occasionally able to kill a Panther through the front turret from 1500 meters.

In the game there's also a very interesting difference between the Soviet 85 mm and German 75 mm shots. Often a single full penetration hit from the German shot ain't enough to stop the target enemy tank, whereas a single partial penetration with the Soviet shot usually knocks out it's target. Why does the 85 mm have so much more stopping power than the 75 mm?

Ari

[Jeff Duquette]

Lorrin:

Sorry I didn’t read through everything. However I wouldn’t have brought this up if your penetration figures were within a couple of mm’s of actual. Even very controlled trials will yield ballistic limit spread in the realm of ~5%. The error as range increases is quite significant. My first take upon looking at pg 49 is that I again suspect your velocity decay assumptions may be in error. I will try to have a closer look at the 122mm APBC ratio this weekend. This is reinforced by the fact that the boundry conditions for your three equations are velocity dependent.

In the mean time you should really consider digging up actual firing tables rather than trying to guess what the decay is. I believe I have indicated on several occasions where this material can be found.

You should also be aware that recently obtained source material indicates that significant hardness changes occurred in Soviet AP between the end of WWII and the mid-1960’s. This would suggest either different metallurgy and/or different manufacturing processes were being employed by post-war Soviet ammunition industry. Using AMMRC data from 1972 “firing trials” (or should I say graph) to represent circa 1941-1945 penetration figures is questionable.

Regards

Jeff Duquette

[Ex Bellator]

Another thanks to rexford for your great reply to my off topic question and the link to the site.

Mike, can I suggest you check out one of the blueprints linked at the bottom of the screen (especially the M42) or look at the picture about halfway down the page (of Factory#183 model).

The blueprint front view really shows that the actual turret front is small and has a big area which is as flat as a pancake due to the mantlet. I'd say you are extremely likely to hit it if you are dead in front of it. However, as you suggest, should this just be one big 'Weak Point'?

It also looks like you would have about a 50% chance of hitting the steeply sloped side turret armour which IIRC is something I don't see in CMBB. However, as rexford says, if the shot scatter is not too great laterally then perhaps that is acceptable anyway, as most shots cluster near the mantlet when aiming at the centre of mass.

[ November 13, 2002, 04:16 PM: Message edited by: Rex_Bellator ]

[rexford]

Jeff,

Your statements are so vague that it is difficult to see what you mean. Put up some numbers from the info you have so we can see what you are talking about. And stop throwing around accusations that are not supported in the same post.

And please stop saying that what you have is correct and everything else is in error. We checked our penetration estimates against all sorts of data and they appeared reasonable, you have one trial that you may be misinterpreting for all I know.

The Russian velocity decreases with range that I use are based on Russian figures we obtained, ballistic equation estimates and other approaches.

You may not know this but practically all WW II velocity estimates vs range are based on ballistic equations, and the results can vary by quite a bit. Use a different methodology and obtain a different number.

"This is reinforced by the fact that the boundry conditions for your three equations are velocity dependent." What the heck does that mean? Another comment that is impossible to interpret.

When velocity is 2200 fps, the equations for 2200-2600 fps and 1800-2200 fps penetration result in 135.6mm and 134.3mm.

When velocity is 1800 fps, equations for 1800-2200 fps and 1400-1800 fps result in 93.5mm and 94.1mm.

I curve fit through areas of the curve that appeared to have the same relationship between velocity and penetration.

"In the mean time you should really consider digging up actual firing tables rather than trying to guess what the decay is."

Which is what we have done, and we filled in the empty areas with other estimates, and then turned the data into spreadsheet friendly equations.

"I believe I have indicated on several occasions where this material can be found." Nonsense. No specifics, just like your posts.

"You should also be aware that recently obtained source material indicates that significant hardness changes occurred in Soviet AP between the end of WWII and the mid-1960’s. This would suggest either different metallurgy and/or different manufacturing processes were being employed by post-war Soviet ammunition industry. Using AMMRC data from 1972 “firing trials” (or should I say graph) to represent circa 1941-1945 penetration figures is questionable."

We were keenly aware of this possibility when we received the 122mm APBC curves about two years ago, long before you received data that suggested it. That's why we thoroughly tested the estimates from the equations before we accepted them for use in the book.

You have totally missed the point on all the material published in our book and on various forums to explain why using post-WW II trials with 122mm APBC appears to be a reasonable approach. While what you say sounds reasonable, use of the 122mm APBC curves results in estimates that closely match Russian figures from 1940 and 1943-1944 tests, post-WW II firing tests against captured American armor, etc, etc, etc.

Until you post some real data and information that clearly shows that my numbers are rubbish, what you say has no real validity. Our figures for T34 76.2mm BR-350B are close to Russian figures from WW II but lower. If you have something that shows that they should be even lower, put it on the table so we can look it over and see if it is as "correct" as you assume.

I posted my methods and info so you, and others, could critically analyze it and challenge it (which you've done without being specific), why don't you do the same?

[ November 13, 2002, 08:01 PM: Message edited by: rexford ]

[Guest Mike]

Originally posted by Rex_Bellator:

Mike, can I suggest you check out one of the blueprints linked at the bottom of the screen (especially the M42) or look at the picture about halfway down the page (of Factory#183 model).

The blueprint front view really shows that the actual turret front is small and has a big area which is as flat as a pancake due to the mantlet. I'd say you are extremely likely to hit it if you are dead in front of it. However, as you suggest, should this just be one big 'Weak Point'? .

I've seen the pictures there (and I've been familiar with T34 geomettry for over 30 yrs now as a modeller and gamer! )

It's not the mantlet that's the problem - the mantlet is 60mm thick.

It's the small vertical plate covering the front of the gun recuperator immediately below the gun barrel.

It also looks like you would have about a 50% chance of hitting the steeply sloped side turret armour which IIRC is something I don't see in CMBB. However, as rexford says, if the shot scatter is not too great laterally then perhaps that is acceptable anyway, as most shots cluster near the mantlet when aiming at the centre of mass.

I take the point about shot scater - however that point assumes that every shot is always aimed at the exact centre of mass.

In fact teh aiming points will themselves have some scatter.

Lastly I can't believe Rexford used his wargaming experience to justify something!! Man that's something I only ever do in extremis, and then only in terms of what the rule author thought something was and comments about the autor's reputation.

I'd never say that the T34 turert was weaker because I can kill it with a 4-6 on a D6 instead of a 5-6 for the hull or something like that!! lol

[rexford]

Originally posted by Ari Maenpaa:

Thank You for the very detailed reply Rexford.

It indeed seems that the cast defiency has been modelled in CMBB as an elite T-34/85 was occasionally able to kill a Panther through the front turret from 1500 meters.

In the game there's also a very interesting difference between the Soviet 85 mm and German 75 mm shots. Often a single full penetration hit from the German shot ain't enough to stop the target enemy tank, whereas a single partial penetration with the Soviet shot usually knocks out it's target. Why does the 85 mm have so much more stopping power than the 75 mm?

Ari

85mm APBC drives a plug into the tank interior that is as wide as the projectile, whereas German 75mm APCBC burster may not explode (they usually didn't in some German tests with angled hits) and the armor breaks off in smaller pieces.

A partial penetration by 85mm APBC probably drives an 85mm wide plug into the tank interior, while 75mm APCBC partials send fragments and less of them than 85mm.

85mm APBC also makes a bigger hole, and has a bigger HE burster. German 75mm APCBC has 0.2% of the weight as HE burster, which is one of the smallest percentages for a WW II armor piercing HE round. German 75mm APCBC has 0.03 pounds of explosive.

[rexford]

Originally posted by Mike:

"Lastly I can't believe Rexford used his wargaming experience to justify something!! Man that's something I only ever do in extremis, and then only in terms of what the rule author thought something was and comments about the autor's reputation."

First off, aim at T34 front will vary from exact center of mass, and that was mentioned in my post.

We use a miniatures system where shot location is measured on a model from the aim point, and takes into account random shot scatter, scatter of gunner aim point, range estimation errors, stupid errors due to human factors, etc. The experience with our wargames was that the T34 turret front area was getting hit alot on that vertical piece below the gun barrel.

This lead us to look into whether it was realistic to have that many hits land on the vertical piece below the barrel, and it appeared to be logical after we analyzed the situation. The wargame bit was brought up as part of our examination of how often the vertical piece should be hit.

When someone says wargame during a research debate, many people discount the findings or conclusions that are drawn. It's expected. We have the most realistic and accurate wargame system for individual shot resolution (whether it hits, where it hits and what it does), and it is occasionally used to help answer questions on this forum.

If someone says alot of T34 turret side armor is visible on turret front shots and about 50% of the shots should bounce off the turret sides, we take our wargame model and I roll the dice 400 or 500 times and tabulate the results. I did this on an earlier thread.

Each roll results in a vertical and lateral drift of the round from the aim point which takes into account all of the factors mentioned above. I also have a computer program which does the dice rolling and range estimating and everything else and outputs shot location from aim point.

Most of the turret hits were bunching up around the vertical center (middle of left to right dimension) at 800m, but quite a few did hit the turret sides. We did the tests with a 75L48 APCBC round which has alot of scatter.

[Guest Mike]

The next question is pretty obvious then - if this point was so weak why wasn't it up armoured?

Ity's relatively small, and I'd think that adding, say 20mm of armour thickness there wouldn't be too much bother - it seems unlikely to be something tht will unbalance the turret excessively, or put too mcuh strain on teh front road wheels??

another obvious question - did the Germans know about this weak point - eg are there instructions to aim for it?

Your modelling sounds impressive, but as with all modelling I'd like to see some backup from teh "real world".

Edited 'cos I just looked up the Russian battlefield to see what they said about it, if anything. There is mention there of the Gun mantlet being a good target - but it's qualified by "at close range" - the main target for the short 50mm is the vertical sides and rear (quoting a report from the Germans date 26 May 1942 on http://www.battlefield.ru/t34_76_3.html). The turret ring is also notes as being vulnerable to being jammed.

So there is some justification for the mantlet being a weak spot, but recommended as targetable "at close range" only.

[ November 13, 2002, 08:57 PM: Message edited by: Mike ]

[rexford]

Originally posted by Mike:

The next question is pretty obvious then - if this point was so weak why wasn't it up armoured?

Ity's relatively small, and I'd think that adding, say 20mm of armour thickness there wouldn't be too much bother - it seems unlikely to be something tht will unbalance the turret excessively, or put too mcuh strain on teh front road wheels??

another obvious question - did the Germans know about this weak point - eg are there instructions to aim for it?

Your modelling sounds impressive, but as with all modelling I'd like to see some backup from teh "real world".

Edited 'cos I just looked up the Russian battlefield to see what they said about it, if anything. There is mention there of the Gun mantlet being a good target - but it's qualified by "at close range" - the main target for the short 50mm is the vertical sides and rear (quoting a report from the Germans date 26 May 1942 on http://www.battlefield.ru/t34_76_3.html). The turret ring is also notes as being vulnerable to being jammed.

So there is some justification for the mantlet being a weak spot, but recommended as targetable "at close range" only.

When the IS-2 glacis was uparmored from 105mm/30 degrees to 110mm/60 degrees,and the nose armor went from 95mm to 127mm at 30 degrees, why wasn't the mantlet and turret front armor significantly boosted in resistance?

Because the IS-2 turret was unbalanced by the large gun, and adding more weight in the form of armor would have played havoc with the whole affair.

The flat area underneath the T34 gun is pretty far out on the barrel and contributes a given moment about the gun rotation point. Add weight and things might not work well anymore.

This is similar to PzKpfw IVH not having turret front/mantlet armor increased when front hull goes from 50mm to 80mm. Why put 82/55 degrees on Panther glacis, which resists 17 pdr APCBC like over 200mm vertical, when the mantlet has 100mm cast? It's all related to weight.

The flat area may be a good target to aim at at close ranges but trying to hit it at 800m is probably going to expend more effort than it is worth. How big is that flat area in a gunsight at 600m?

German crews trained to aim at intersection of turret and hull, where even a 37mm AP hit could damage the turret race on KV and T34 tanks.

We have compared the results from our ballistic model to combat results and they are close. At close range, when one aims at the center of mass (T34 or Panther glacis), very few shots will strike the turret because:

A. shot to shot scatter is extremely small

B. variations in aim point are small

C. errors in range estimation are small and round tends to hit close to aim point

D. trajectory is flatter at close range so errors in range estimation have less effect on vertical placement of shots

We have read about a 75mm armed Sherman that was firing on and hitting a Panther on the glacis at close range. After this went on for awhile the Panther commander spotted another Sherman to his flank and rotated the turret onto the second Sherman and drilled it.

While the Panther was rotating its turret and firing the first Sherman kept hitting the same glacis area, shot after shot.

How many wargames decrease the percentage of total hits that land on turret as range decreases?

And the percentage of track hits that occur at close range will be small, compared to longer ranges, when a tank is pointed directly at the firing gun. Due to abovenoted reasons.

Our wargame took over 15 years to develop and is based on alot of research and analysis.

[Amedeo]

Originally posted by rexford:

<cut>We have compared the results from our ballistic model to combat results and they are close. At close range, when one aims at the center of mass (T34 or Panther glacis), very few shots will strike the turret because:

A. shot to shot scatter is extremely small

B. variations in aim point are small

C. errors in range estimation are small and round tends to hit close to aim point

D. trajectory is flatter at close range so errors in range estimation have less effect on vertical placement of shots

<cut>

How many wargames decrease the percentage of total hits that land on turret as range decreases?

I think this statement, although a side note in this thread, should deserve special attention.

Maybe a range dependent turret hit probability is something PFC should seriously consider for the next CMBB patch (I'm assuming this feature is absent in the current model).

Regards,

Amedeo

[rexford]

The probability of hitting a tanks' tracks is greatest when front of vehicle is at 30 degrees angle to the firing gun aim, which places the front track area in direct line with the gun barrel (below the center of mass).

As range increases, ground folds (small rises and valleys) tend to block out a firing guns line of sight to the bottom areas of the target tank (tracks and front lower hull). At Isigny, firers had trouble seeing enough of the Panther front lower hull armor to hit it and ranges were 200 to 800 yards. If they couldn't see the front lower hull well in very case, they couldn't see much of the tracks either.