Tiger I armor plate quality

[Yoozername]

The report above is interesting but it seems to deal with Non-German munitions? They talk about the windscreen being screwed onto the cap. In German Pzgr, the windscreen is a press-fit crimp and would yield easily. I really doubt it is going to impart much of anything to the main mass.

This image is an actual 8.8 cm Pzgr that has been cut open with 1/4th the projectile removed. Note the crimping of the windscreen, the thin material of the windscreen also. The mass of that cone is miniscule compared to the rest of that projectile. The mass would push through the crimping and ride through the windscreen.

The M62 drawing above has a hollow area under the windscreen perhaps 4X the German one. The German Pzgr uses sloping sides on the cap to act as a 'windscreen' necessitating just a small cone on top. The US projectile has somewhat uniform cap thickness that might decap the projectile when attacking sloped armor.

88crimp.jpg

[Peasant]

There is something very interesting I found: if, according to document posted by Miles, the M62 shell, w/o windscreen and the relative yaw issues, has the Navy BL of 1774fps against Tiger I superstructure plate, then the 75mm M61 shell would have the Navy limit 1781fps(DeMarre) which is equivalent to the range of 750m(!) when fired at 2030fps. In soviet trials the Tiger I side was defeated once from 400m, (75mm external diameter AND 15(!)mm internal diameter of the hole with a 300x300mm disk thrown from the back of the plate) which means attacking shell didnt enter inside the vehicle.

So after realizing this I went to check the report of this trial and there you go: the initial velocity for the M61 shell is listed as 564m/s(1850fps)!
The actual distances for the 75mm M3 gun w/ 2030fps muzzle velocity would not be 400m and 650m but 950m and 1200m respectively.

This is less than Terminal Ballistics reports for 3,22in/0° of the US RHA which is 1860fps.

Edit: Oh, yes it all comes together: the soviet document also report the propellant weight as 0,875kg while the "Catalogue of Standard Ordnance Items 1944" list the propellant weight for the M61 round as 2,16lb. or 0,98kg.

Edit2: These values are consistent with the distance reported here:

Source:http://www.matrixgames.com/forums/fb.asp?m=3017080

[Peasant]

Another thing: In the Tiger II trials by soviets, the US 76mm gun holed the Tiger II lower side armour (80mm/0°) only once out of the two shots directed at it with the striking velocity equivalent to 2000m range or, assuming the ballistic of the M1A1/M1A1C gun, 1916fps which fits nicely with the 1960fps Prot/Army limit for the yawed M62 shell.

[Peasant]

On their own these results are not very helpful for assessing the quality of these armor plates, so I've compared them in graphical form to the US RHA acceptance specifications taken from this document: https://apps.dtic.mil/dtic/tr/fulltext/u2/128818.pdf

[Peasant]

Another thing: In the Tiger II trials by soviets, the US 76mm gun holed the Tiger II lower side armour (80mm/0°) only once out of the two shots directed at it with the striking velocity equivalent to 2000m range or, assuming the ballistic of the M1A1/M1A1C gun, 1916fps which fits nicely with the 1960fps Prot/Army limit for the yawed M62 shell.

Okay, disregard what I just said here. Those shots were directed at the upper side armour (80mm/25°). Every shot directed at lower side armor penetrated up to and including "range" of 2000m.
Terminal Ballistic Vol.III give the BL(N) for M62 APC against 80mm/25° as 1990fps. Given the less than optimal armour quality of this specimen of Tiger II a BL of 50-100 fps less is very plausible.

[Peasant]

On the topic of stability of M62 projectiles:

The spin imparted to the projectile is a product of rifling twist and muzzle velocity. When the projectiles were fired at velocities lower than what they were designed for, the resultant spin was insufficient to keep the yaw within acceptable limits, which resulted in degraded anti-armor performance.

This might seem like it would imply that as projectile slows down with distance, it's spin would decrease proportionally, but is it the case? If you analyze carefully the forces in play, you will see that all forces acting on the surface of the shell due to drag, are acting in longitudinal plane and their vectors are always perpendicular to the direction of rotation of projectile. Therefore, they can't perform any work and cannot slow it's rotation down.

Therefore, I conclude that the projectile will not in fact loose any appreciable amount of spin at any reasonable distance and it's anti-armour performance will not suffer compared to the same projectile w/o windshield fired at a lower velocity.

[Yoozername]

It does not not look like a M62 at all?

[Peasant]

It does not not look like a M62 at all?

What gave it away? Maybe the text written in large font: "SHOT, AP, 90-MM, M77"? The difference in design doesn't matter, the theory applies to all spin stabilized projectiles. I've just used plain AP to make my schematic more simple.

[Yoozername]

Therefore, I conclude that the projectile will not in fact loose any appreciable amount of spin at any reasonable distance

I agree, when It is fired, generating spin, and striking a target possibly 1 to 2 seconds in most cases, it does not even have time to lose spin. A mass like that, spinning at that rate, would need a tremendous force to make it slow down. Long range artillery might take that into consideration. In fact, after penetration, the projectile is still spinning. The powder charge puts a majority of energy into the translational velocity, but also a good amount into the spin. I used to work with spindle motors. Getting any mass up to 20 to30,000 RPM takes a great deal of energy.

..and it's anti-armour performance will not suffer compared to the same projectile w/o windshield fired at a lower velocity.

Not sure what that means? What does spin have to do with this?

I think you should look into effects of center of mass and nutation. Also, the phenomena of projectiles initially coming out of the barrel and requiring some distance to stabilize forward motion and orientation. The use of muzzle brakes showed that projectiles 'uncork' with enough misalignment that they would hit the brake with driving bands and shoot back metal at the commanders.

IMO the M62 design is pretty bad compared to the Pzgr 39.

[Yoozername]

I guess there are windshields and then there are windshields.

75.jpg

Again, compare the designs. Look at the mass. The German design center of mass specifically.

[Peasant]

..and it's anti-armour performance will not suffer compared to the same projectile w/o windshield fired at a lower velocity.

Not sure what that means? What does spin have to do with this?

I think you should look into effects of center of mass and nutation. Also, the phenomena of projectiles initially coming out of the barrel and requiring some distance to stabilize forward motion and orientation. The use of muzzle brakes showed that projectiles 'uncork' with enough misalignment that they would hit the brake with driving bands and shoot back metal at the commanders.

IMO the M62 design is pretty bad compared to the Pzgr 39.

Interesting fact. Where can I read more? Google is not forthcoming with useful results.

My reasoning is: I assume that M62 shell as designed(w/ windshield attached) does not suffer excessive(compared to shell w/o windshield) yaw when fired at service m.v.(2600fps) at any distance. The Americans have extensive experience in designing Naval shells, and this is not an issue with their other tank/At guns. Only when fired at reduced m.v. there is an excessive yaw. Since the suggested solution to this problem was to fire the shells from a gun with bigger rifle twist, I assume a faster spin rate would solve this problem.

[Peasant]

Here are the figures for the 1942 DHHV tests of its Tiger plate and those from the Aberdeen tests of 3 Tigers. and pages 2 and 16 from the ABL report. Note that 1 of the 5 original DHHV 37HB75 plates was superior (in green), 2 inferior (in red), 1 of the 3 37HB75 Aberdeen plates and 1 of the 3 newer DHHV C81 plates superior, 1 inferior. Of the 5 Krupp PP718 plates, 3 were superior, 1 inferior.

The uncharacteristically high BL(N) against Tiger I driver plate by M72 shot (1991fps) makes me believe it suffered serious damage while trying to penetrate through this target, degrading it's performance. An intact M72 shot would have closer to 1800fps BL(N) against 4in./0° (estimated).

[Yoozername]

Interesting fact. Where can I read more? Google is not forthcoming with useful results.

There is a great deal that may edify you.

But answer my question above first?

[Peasant]

Interesting fact. Where can I read more? Google is not forthcoming with useful results.

There is a great deal that may edify you.

But answer my question above first?

You didn't ask one. Ask away.

[Yoozername]

..and it's anti-armour performance will not suffer compared to the same projectile w/o windshield fired at a lower velocity.

Not sure what that means? What does spin have to do with this?

I think you should look into effects of center of mass and nutation. Also, the phenomena of projectiles initially coming out of the barrel and requiring some distance to stabilize forward motion and orientation. The use of muzzle brakes showed that projectiles 'uncork' with enough misalignment that they would hit the brake with driving bands and shoot back metal at the commanders.

IMO the M62 design is pretty bad compared to the Pzgr 39.