HVAP Slope Effects Need Fixin'

[Paul Lakowski]

90mm gun demonstrated only a 50% penetration ability Vs Panther glacis @ 2-300 yards [Faint Praise,pp90]

"Gillem's figures , provided by the Ordnance Department were fantastically optimistic.

Americans in combat found that the 76-mm and 3 inch guns might penetrate a Tiger at 50 yards , but were both considered to be generally ineffective against the frontal armor of the Tiger"

.......

"Through out the war the Ordnance Department fired its guns against nearly vertical plates of armor to establish their penetration capabilities.The hardness of the test plate did not match that of German armor. More importantly , the Ordnance Department accounted for angled armor by geometrically calculating the increased effectiveness of the angled plate. Then extrapolating a gun's penetration capabilities based on performance against vertical plate, they calculated its capability against slanted armor. This technique failed to account for the tendency of projectiles to ricochet from angled plate.For example , the horizontal thickness of a plate of vertical steel is doubled when the plate is slanted at 60°, but its resistance to penetration is tripled because of ricochet.[pp90]"

"The three inch guns had a chance against the turret mantle at a very short range , 200 yards .Only the 90mm gun and the 105mm howitzer proved capable of penetrating the Panther's glacis plate....The 90-mm gun was credited with penetrating the Panthers front from 600 yards . But even this was disputed in a later test. The 703rd Tank Destroyer Batttalion with M-36 tank destroyers firing in early december 1944 was only able to make penetration about half of the time at ranges of 150-300 yards."[pp106 & 107].

The longer the nose cone the more slanted penetration can turn the projectile and lead to increased path through the armor or even riochet.The Germans were the first to recognize this in WW-II when the moved to APCBC ammo, the ratio of the diameter of the tip to the diameter of the body change from 10:1 or more down to 4:1 to 5:1 and the interior projectile was cap with a blunted shape piece. The impact was to reduce the stress on slanted impact. The Russians where the next to recognize this with the BR-350A which featured 6:1 tip to body ratio and blunted cap. But the americans didn't clue in until after the war.The M61 had tip to body ratio of 15:1 with a conical ballistic cap.Same construction is seen in the 76mm M-62 & 90mm M82 APC rounds.

It had direct impact on the slanted performance of the ammo

Wa Pruef Report on APCBC penetration at angle similar to Jentz figures.

500m/s

30deg 0.866^ 1.26

45deg 0.707 ^ 1.4 60deg 0.5 ^ 1.26

800m/s

30deg 0.866 ^ 1.26

45deg 0.707 ^ 1.7 60deg 0.5 ^ 1.45

1000m/s

30deg 0.866 ^ 1.26

45deg 0.707 ^ 2.5

60deg 0.5 ^ 1.5

90mm APC 700- 750m/s

@ 30° 0.866^1.45

@ 45° 0.707 ^1.75

@ 60° 0.5 ^ 1.75

90mm HVAP 1000m/s

@ 30° 0.866 ^ 1.7

@ 45° 0.707^ 2.2

@ 60° 0.5^ 2.4

Russian @ 30°

BR-350 ^1.26

BR-350A ^ 1.25

BR-350B ^0.9

BR-354P ^0.85

BR-412

@ 30° ^ 1.3

@ 60° ^ 1.3

The reason the HVAP round suffers @ slanted impact is due to the very sharp nose shape and that this is aluminmum encased Tungsten projectile. Aluminum is an appaliing penetrator material suffering from thermal softening at penetration temps.

The sharpness leads to shatter at angle leading to aggrivated penetration route through the angled plate, @ 60° this should be 0.5^2.4 or thickness ÷ 0.19 times [ > 5 times thickness].

The APDS has a rounded penetrator this lowers the shatter or its transitional velocity [remember that word?].Consequently its penetration route is much closer to the LOS.

The effect of the nose shape disappears after the projectile has penetrated two diameters .Now if the projectile is a full caliber 2-3:1 L/d APC type shot then this has a more dramatic effect than a APDS penetrator that are usually 4-5:1 L/d.

[This message has been edited by Paul Lakowski (edited 01-17-2001).]

[Simon Fox]

<BLOCKQUOTE>quote:</font><HR>We had other firing test results from WW II British sources on APDS dispersion, and it seemed to easily be the most inaccurate ammo used during WW II.<HR></BLOCKQUOTE> You'll get no argument from me on this point although I would hestitate to rely on anything other than general impressions from the Isigny tests. The British tests also clearly demonstrate this and appear more rigorously conducted. The real question IMO is how to model and quantitate it and finally what effect that might have on the TacAIs choice to use it.

Did the British do any side by side accuracy testing of 76mm HVAP and 17lbr APDS since they did have both in Shermans?

I am also concerned that HVAP and APDS don't get lumped together. As Paul's post shows and as rexford eventually acknowledged above the slope effects are (and should be in CM) different for the two rounds.

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Muddying the waters as usual.