CMRT penetrations on highly sloped armor

NUTTERNAME

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These two Panzer IV got it in back to back turns. 45mm at 650m.
One got a roofie hit and also a track hit on the glacis. Look by the bow MG barrel.
The other got multiple glacis hits and include a 'track hit' also.
Regular AP penetrations.

There was another Panzer IV that got 3 76mm infantry gun hits in a row on it's roof. At 500 meters, that's mighty fine shooting!

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NUTTERNAME

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A Panzer IV that shows detail of the hatch lock. Also other mounting points on glacis. An example of an internal explosion I would presume. The driver's side has blown out. Nearest glacis hatch blows open, and the middle plate (bolted) also has taken off. RO side hatch has stayed closed. The whole upper structure has lifted and landed off orientation. This includes the turret.

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NUTTERNAME

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It's a far cry from dots on tanks.
The dark spots in CMx3 denote penetrations. The 'gouges' (grey) denote non-penetrations. They are sized by caliber. Supposedly, the actual area hit is modeled or at least represented in the graphics. I am not sure if you have the demo.

Do you have any comment in regards to a 45mm ATG either getting multiple hits on the glacis or the penetrations at 650 meters?

I posted the picture of the last panzer IV to show details of the area under question. Also, it shows a typical catastrophic event from an internal explosion.
 

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This panzer IV was hit by a 45mm ATG at 650 meters. It has been hit three times. One hit is on the track that covers the center panel on the glacis (It is the black area). The other two hits are the black holes on the glacis.

I have no idea what destroyed the panzer IV that is missing it's left side suspension and final drive, etc. (if that is what you mean?)

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mOBIUS

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Even a 45mm/L66 shouldn't be able to penetrate that front plate from 650m with APBC or APCR.

Actually, this may be a jump ball. Running this through Okun's homogenous armor program the 45mm doesn't penetrate. But running it through the face hard armor penetration program has it a partial pentration with part of the body penetrating but breaking up.
 
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NUTTERNAME

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Even a 45mm/L66 shouldn't be able to penetrate that front plate from 650m with APBC or APCR.

Actually, this may be a jump ball. Running this through Okun's homogenous armor program the 45mm doesn't penetrate. But running it through the face hard armor penetration program has it a partial pentration with part of the body penetrating but breaking up.
I suppose my question is "How often does the 'face hard' program predict ricochets to occur?". It's simply impossible to predict 'a partial pentration with part of the body penetrating but breaking up' as an outcome. I assume you ran APHE and not APCR.

Basically, if I were modeling this, the psuedo-code would be...

Where is the hit located
What is the obliquity
Run ricochet routine
If No ricochet
then run penetration routine
If penetration, then run damage routine...etc.

An interesting aspect of the whole event is the kinematics regarding the translational movements, rotational movements and the actual time lapse of the event. The projectile is spinning at a tremendous rate. Something on the order of 10,000 RPM. Given the weight of a 7.62cm APHE (12 pounds?), this is a lot of energy involved. I've read that rifled weapons puts about 1/6th of the energy of the gunpowder into rotation of the projectile, the rest going into translational velocity and friction. In most cases, such as a projectile striking armor at an angle of 60 degrees, the amount of rotation the projectile experiences during the penetration event is insignificant. But when striking a highly sloped plate, the event is much longer and the rotation does come into play. As an example of time, we are talking on the order of a tenth of a millisecond (100 microseconds).

My take on the 'flat nosed' projectile striking a highly angled plate is that the contact point is not only small, almost a 'stripe' of contact is being made, but the contact is being worn while the actual armor being 'worked' is being 'renewed' as the projectile slides along the plate. When striking a more 'vertical' plate, even something like 45 degrees, the rest of the projectile's frontal area is rapidly brought into play. Something like 10 microseconds or less. The rotation of the projectile during such a small amount of time might be a degree or so.

But when a projectile is 'sliding' along a plate, attempting to dig in, the projectile rotation does come into play. Especially if the initial projectile contact area has become worn or broken. The reason being that the new projectile contact area (from rotation) will ride up as it replaces the worn area! This will be constantly happening as the projectile rides along the plate. Also, the rotational forces are effected by loss of material in the symmetric projectile. If a substantial piece comes off, as these Soviet designs appeared to be designed for, then the projectile becomes unstable as far as translational movement and being pointed in the direction of travel. Also, the projectile will start to rotate (yaw). An interesting point is that one study showed that faster rotating bodies actually promoted ricochet.

The projectile is reduced to striking the plate and either cracking it through shock or another failure mechanism.
 
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mOBIUS

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I'm not sure face hard is a good model for this. In that I had to modify the program to accept smaller thicknesses. The original program doesn't allow anything less than 2". My 45mm round test is for something 3.4lbs, 1.77" striking at 2150f/s.

Actually, I was modelling using crappy armor. If I use good stuff like Class'A' or German Bismarck armor it doesn't penetrate.
 
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An interesting aspect of the whole event is the kinematics regarding the translational movements, rotational movements and the actual time lapse of the event. The projectile is spinning at a tremendous rate. Something on the order of 10,000 RPM. Given the weight of a 7.62cm APHE (12 pounds?), this is a lot of energy involved. I've read that rifled weapons puts about 1/6th of the energy of the gunpowder into rotation of the projectile, the rest going into translational velocity and friction. In most cases, such as a projectile striking armor at an angle of 60 degrees, the amount of rotation the projectile experiences during the penetration event is insignificant. But when striking a highly sloped plate, the event is much longer and the rotation does come into play. As an example of time, we are talking on the order of a tenth of a millisecond (100 microseconds).
The Russian F-34 76.2mm gun has a rifling of 1 rotation per 25 calibers. The US 76mm is 1 per 32.
 

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The Russian F-34 76.2mm gun has a rifling of 1 rotation per 25 calibers. .
Maths work out very close to 10K rpm for F-34. 41.6x76.2=3.17 meters. Time in tube is approx 9.75 mS. 1.664/0.00975=170x60=10,200rpm or so
 

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76.2mm x 25 = 1905mm.
One rotation for every 25 calibers is one rotation each 1.905 meters.
With a MV of 655m/s for the BR-350B then that is 655/1.905 = 343.8 rps.
Or 20,629 rpm. That’s a lot of rotational KE and stability. It is fighting not to ricochet.
If the edge is chipped it might just bite into the armor like an Uruguay soccer player into an Italian and retain its direction.
 

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76.2mm x 25 = 1905mm.
One rotation for every 25 calibers is one rotation each 1.905 meters.
With a MV of 655m/s for the BR-350B then that is 655/1.905 = 343.8 rps.
Or 20,629 rpm. That’s a lot of rotational KE and stability. It is fighting not to ricochet.
If the edge is chipped it might just bite into the armor like an Uruguay soccer player into an Italian and retain its direction.
Yes, I flubbed 'barrel time'. It should be 1.905/0.0059=323 rev/s x 60=approx 20K rpm.

It is fighting not to ricochet? That needs more discussion.
 

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It is fighting not to ricochet? That needs more discussion.
The gyroscopic effect to maintain its line of travel. Hmmm, come to think of it. It might also fight not to normalize into the plate as much as imagined. I've only seen strobe xray photos of blunt nosed long rod penetrators normalizing into highly angled plates. They are fin stablized so there is no rotation going on.
 

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The gyroscopic effect to maintain its line of travel. Hmmm, come to think of it. It might also fight not to normalize into the plate as much as imagined. I've only seen strobe xray photos of blunt nosed long rod penetrators normalizing into highly angled plates. They are fin stablized so there is no rotation going on.
Yes, my thoughts also. The whole 'normalization' concept is made worse by that awful little cartoon showing the projectile changing direction outside the armor (Soviet website?). The change in penetration direction, for a WWII AP type projectile, actually takes place within the armor as the projectile follows the path of least resistance.

I must also comment on some of the reading I see that people say 'drill' into the armor. Drills, at least the ones I use, spin very fast but penetrate into the material very slowly. The exact opposite happens when a AP is striking the armor. The rotation is very slow in the process of penetration. The mechanism for penetration is either plugging or forcing material out of the way.

Projectiles are spun mainly to have stability. It is a case of "enough is enough" and more is not the goal. Too much spin will bring out defects in mass in the projectile and cause wobble, and other unwanted effects. Basically, the smaller the projectile, the more spin needed. Large artillery shells, with great mass, do not want or need great amounts of spin. In fact, since they have to vary the charge, rifling must be a compromise of sorts.

But spinning masses are gyroscopes and will respond to disturbance forces as such. Losing mass, especially on the outer edges, is not good. Also, forces acting on the outer edges, will have corresponding effects on the 'gyro'.

It is also a force that does not like to stopped. I am amazed at photos that show embedded rounds that appear to have stopped in a few inches of armor. Not only the translational velocity has been 'swallowed' by the armor, but that rotational energy has gone from spinning 20K rpm to 0 rpm in perhaps tens of microseconds.
 

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The Russian F-34 76.2mm gun has a rifling of 1 rotation per 25 calibers. The US 76mm is 1 per 32.
As a comparison, the PAK40 has a progressive (and aggressive) rifling of 1/24 to 1/18. The KWK40 L48 was a constant 1/22.

Even tank and antitank guns are tasked with firing a variety of ammo with differing velocities. A PAK40 75mm antitank gun firing APCR (if it had one to fire), is really spinning the spit out of the projectile. And also stressing the tube. The Germans certainly standardized the KWK40 and KWK42 to fire HE at a lower velocity. Makes sense since tanks actually fire a lot of HE.
 
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Speaking of the German 75mm. The British captured a lot of 75mm APHE round in N. Africa. They then converted them to be used by the Grant's 75mm by lathing down the driving bands. There was worry that the spinning lathe would arm the round. But a lathe spin around 1500-1800 rpm. A lot less than the fired rounds potential. So no wonder the shell wasn't armed.
 

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yeah right...

[video]http://www.flamesofwar.com/Portals/0/all_images/weapons/AT-apcbc.gif[/video]
 

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The penetrations are still modeled against highly sloped armor. I did a quick test and one Panzer IV received a hit on it's turret roof, deck roof and two hits on it's bow 'roof'. All were penetrations by 45mm ATG at about 500 meters. Normal AP.
 

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I was interested in doing a test with a hull down StuGIII getting shot at by a 45mm ATG. I wanted to see what effects it might have on the highly sloped armor on either side of the gun. I was able to make a test with a 500 meter range. I drove up a StuGIII with a small covered arc and buttoned and the 45mm started shooting. The ATG never hit the sloped armor at all. It hit the 'weapon mount' and 'weapon' close to 20 times. But, since it was a late model StuG with the cast mantlet, I was surprised that the 45mm was penetrating. It seems the game models dispersion in very tight groups. I really doubt that 45mm would penetrate the StuG 'pig's head' mantlet.


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