CMRT penetrations on highly sloped armor

NUTTERNAME

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A guy who researches that quite a bit is saying that the hardness doesn't matter as much at high angles.
http://www.ww2aircraft.net/forum/ww2-general/german-75mm-v-allied-75mm-37327-4.html
I'm not so convinced.
Those guys at BF are using Lorrin Birds formula for Russian APBC shot which he developed by scaling that graph. In fact that is who originally posted that 122mm graph.
The only other high angle data I have is from modern tests (Military Technology magazine) of long rod penetrators during the late 1990's. Blunt rods do indeed have an effective high slope penetration less than the cosine rule. But not that much less, like only 10-15 degrees.
I will have to check it out.

I suppose the whole ricochet modeling vs. armor penetration modeling is what I am getting at. The Germans did not like testing at high obliquity since they could not get reliable results. But that is an effect of ricochet. The smallest factors, such as projectiles not flying in the projectile path (pitch and yaw, etc.) mess with expectations at extreme angles. Shape of projectiles and what hits first, also mess with expectations. The Germans didn't like testing against face hardened armor either. It was not easy to make consistent FH armor like it is with homogeneous armor.

By the way...is that a M79 or M61 round stuck in the armor of the jagdpanzer IV(A)?
 

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I will have to check it out.
By the way...is that a M79 or M61 round stuck in the armor of the jagdpanzer IV(A)?
Can't tell.
The only formula that I have which says anything about high angle penetrations and uses T/D is Nathan Okun's M79APCLC. Assuming good generic armor and then working backwards from NBL to ballistic Impact Vel. it looks like the 25mm @ 73° is equavalent to ~72mm for the M79 shot round.
[Edit] Make that ~72mm I had the weight 1lb short.
 
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NUTTERNAME

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A guy who researches that quite a bit is saying that the hardness doesn't matter as much at high angles.
http://www.ww2aircraft.net/forum/ww2-general/german-75mm-v-allied-75mm-37327-4.html
I'm not so convinced.
Those guys at BF are using Lorrin Birds formula for Russian APBC shot which he developed by scaling that graph. In fact that is who originally posted that 122mm graph.
The only other high angle data I have is from modern tests (Military Technology magazine) of long rod penetrators during the late 1990's. Blunt rods do indeed have an effective high slope penetration less than the cosine rule. But not that much less, like only 10-15 degrees.
I found some pretty good info as far as ricochet modeling. I have to do a bunch of data unit conversions and number crunches.

But the whole high angle obliquity of a round shape (BR-354B less windscreen) is actually looking at a very small area of the monobloc AP making initial contact on a very small part of the projectile (the 'lip'). Neglecting rotational angular change, during the first few centimeters of contact travel, a very small part of the penetrator is being subjected to tremendous forces. Unlike a 45 degree hit (for example), where the 'shared-load' across the front of the penetrator is rapidly taking place, a high obliquity hit will keep a small lip of the AP under the same forces 'for awhile'. It is quite analogous to the face hardened armor defeating pointy tip AP.

Any 'grinding' away of that small lip area just produces a bigger ramp just like the ogive area. In other words, it would need to stay intact to dig into the armor to have a chance. But the ogive area is fighting it.

An interesting thing comes into play. Any loss of material that changes the shape of the AP, if it is not equal through a perspective of the axial line through it, will make the penetrator unstable and the rotaional forces will come into play and create instability. I don't quite buy into the whole Soviet scheme of spewing off frontal shot areas to make blunt out of a pointy penetrator btw. It would have to be fairly uniform and I doubt that is achievable.

It may seem strange, but the rotational forces (usually neglected), play into ricochet. If I understand some of what I have read, it seems higher rates of angular velocity actually increases ricochet at low angles of obliquity!
 

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As far as that guy's stuff...It's good info and new to me. But, I have been convinced that the German 75mm AP is the 'gold standard' as far as WWII already. They MUST have been the most produced AP (over 37mm), most used (projectile was shared between PAK40 and KWK), and probably had the most number of soldiers trained on them. Basically the backbone of the Germans high velocity antitank efforts.

And, from the Yugo shoots, it handled T34 sloped armor fine without going 'blunt'. I have read of accounts where they shot through tanks, hit a stone wall and landed on a road, still spinning, and looking intact less the windshield. But it would still have issues attacking 20 degree or less sloped armor IMO.

I will read through that whole thread again. Just have to check to see how 'JasonC' he might go with the data. It's great to make theories, but it needs to be backed up.
 

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As far as that guy's stuff...It's good info and new to me. But, I have been convinced that the German 75mm AP is the 'gold standard' as far as WWII already.
He does have access to German documentation I've never seen before.
 

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An interesting photo of a Panzer IV that has been severely damaged by artillery hits. It looks like it took at least a direct hit on the drive sproket and one on the glacis. Note the bowed plate. The one open hatch appears rather sturdy. The tanks suspension appears to have failed as if it was crushed downward. The superstructure seems to be in place. I doubt there was an internal ammo explosion that is often seen in Panzer IV pictures. The mangled drive sprocket shows that many suspension parts and other external parts on tanks are not armored.

View attachment 46376
 

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An interesting photo of a Panzer IV that has been severely damaged by artillery hits. It looks like it took at least a direct hit on the drive sproket and one on the glacis. Note the bowed plate. The one open hatch appears rather sturdy. The tanks suspension appears to have failed as if it was crushed downward. The superstructure seems to be in place. I doubt there was an internal ammo explosion that is often seen in Panzer IV pictures. The mangled drive sprocket shows that many suspension parts and other external parts on tanks are not armored.
If indirect fire its likely only one hit caused all that front-side damage.
 

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That Pz IV looks more like a hit from an airplane bomb to me.
 

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I really believe that an artillery shell has struck the sprocket/track, broke the track and mangled the sprocket, and then detonated further back by the rear bogies. Note the condition of the first bogie right behind the sprocket. I don't think the tank had an internal explosion and the crew seems to have bailed.

But the other hit on the glacis shows that the armor was pushed down and appears not to have cracked. In any case, that glacis armor is not welded to the vertical front armor. The tank might be in North Afrika. the jagdpanzer IV (A) may be a case of crappy late war armor.
 

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I don't think there was a hit on the glacis. If one shell did all the damage on the roadwheels and sprocket and the same kind of shell hit the glacis it would of totally destroyed the glacis. I think the hit on the sprocket caused enough blast pressure to bend in the glacis. Maybe the shell explosion started at the fender level.

What's with the destroyed roadwheels and return roller wheels toward the rear? I don't know, maybe a near miss of another shell in that vicinity. Then internal fires often weaken road wheel mounts. Looks like the rubber has burnt off the rubber of some road wheels. So maybe just the one hit that cause a fire.
 
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I don't think there was a hit on the glacis. If one shell did all the damage on the roadwheels and sprocket and the same kind of shell hit the glacis it would of totally destroyed the glacis. I think the hit on the sprocket caused enough blast pressure to bend in the glacis. Maybe the shell explosion started at the fender level.

What's with the destroyed roadwheels and return roller wheels toward the rear? I don't know, maybe a near miss of another shell in that vicinity. Then internal fires often weaken road wheel mounts. Looks like the rubber has burnt off the rubber of some road wheels. So maybe just the one hit that cause a fire.
The glacis hit may have bounced off. Especially if set on delay fuse. If it ricocheted under the front armor, and detonated inside the tank, there would be no tank left. the tank appears to not have had an internal fire (the turret looks very clean). and the suspension is not sagging IMO. The return rollers have been taken off and I believe the bogies have been broken away. One appears to have been cracked off. I think the parts behind the soldier are also suspension parts. Not likely an internal fire but some of the rubber is removed and possibly charred.

If the hit on the sprocket was a super-quick fused shell, there would be great fragmentation damage especially to the bent back fenders. For the blast effect to push that glacis plate down seems to indicate it changed direction of force.

Panzer IV crews certainly used tracks as additional 'armor'. More so than most panzers. The glacis plate would certainly be vulnerable to indirect HE and large AP strikes. But to get back on topic...I don't think a Soviet 76mm AP (whatever type) would pose a threat at 1000+ meters to this plate. I have seen G models that have a lip between the glacis and vertical front armor. i will have to look at H models more closely. And to be clear, I don't think ALL ap is going to skip off the plate. I am sure a 122MM projectile (take your pick) will have definite results no matter what.
 

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I must have a bug in my remake of Okun's M79APCLC program. I ran his program in it's native BASIC and found that the Russian 76mm APBC will not penetrate the 25mm glacis at any range. It will penetrate the 20mm glacis only at under 50m.
 

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I must have a bug in my remake of Okun's M79APCLC program. I ran his program in it's native BASIC and found that the Russian 76mm APBC will not penetrate the 25mm glacis at any range. It will penetrate the 20mm glacis only at under 50m.
Thanks. I assumed that 1000-1500 meters was outside a penetration model of calculation (in addition to a ricochet model) of most models perhaps?

This is interesting research as far as ogive ricochets at low obliquities. But I would like to say some things regarding the target itself, before stating my position.

target:
Thickness of the 'carrier plate' is 20-25mm. It has three openings. It may lay at a marginal overlap with the more-vertical 'bow armor' and present a vulnerable area. The later model (H or J?) under question in CMRT has the 'scooped' hinged 'brake' covers. These appear to be a thicker version of the earlier covers, with different 'handles' or 'air vents'. The center 'flush' plate appears to be bolted down and not hinged. It is actually designed to have tracks over by designed in holders. I think it may be the same thickness as the maximum carrier plate thickness. But present some weak areas in joining.

The carrier plate has openings that show a ledged area . There may be an overlap regarding the 'brake covers.
 

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The good news is that I found the bug in my program. A 17 lb. 3" shot vs 1" @ 75 degrees has a limit velocity of 2737 ft/s.
 

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A 17 lb. 3" shot vs 1" @ 75 degrees has a limit velocity of 2737 ft/s.
That 'curve' is from one data point. That is a joke that engineers use on calibration techs. "He can draw a strait line with one point and a ruler..."

It makes me wonder if they only fired one round? Maybe they fired more and the others ricocheted? It is a very odd report if the X and + and * are the only data. I thought the Brit's criteria was a 50% through and 50% other? You can't get 50% without two data points.
 

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British criteria for a penetration is 50% chance that 20% of the shell mass goes through armor. That is for a 2-pr test. Later tables had something like an 'armor holed' criteria. Penetration Table with label of ''perforative".
 

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Interesting report that addresses the shapes of penetrators as far as bluntness.

http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0916925

I have to say that there are a couple of odd things with the report. They include data for projectiles that are produced too heavy by a miscalculation. They also monitor yaw, which is great, but don't include that data. They throw it out. It's one of the causes of real world ricochets. But I suppose they assume that they are modeling reality. They also control velocity through charge weight changes. While this may not seem to be a problem, with a fixed rifling, it actually changes the rotational spin as well as the translational velocity. Rotational velocity in real life does not get 'scrubbed' as fast as translational velocity.

But it is a good read even for most maths-challenged wargamers. Flat nosed AP are basically trying to punch out a plug in the armor as well as trying to get inside. I believe that plugs actually have equal or greater velocities in most cases. Since the AP has scrubbed it's energy getting into the armor, it makes sense that the plug has received much of it.

The dividing by the cos of the obliquity is very interesting as far as finding the ballistic limit velocity from just using the normal angle data.
 
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