American and German 75 mm AP Quality

Discussions on the vehicles used by the Axis forces. Hosted by Christian Ankerstjerne
Miles Krogfus
Posts: 308
Joined: 08 May 2015 19:54
Location: San Diego, CA

American and German 75 mm AP Quality

Postby Miles Krogfus » 21 Jan 2016 20:51

I give nose and center line (nose to HE cavity) Vickers Diamond Hardness (VDH) figures:
M61 APC from Roper, lot 200S 640/631, lot 300S 549/535, lot 700S 619/549, lot 800S 630/521. 1 lot superior nose quality (640) 2 lots good, 1 lot poor (549). 1 lot superior CL (631) 1 good, 2 poor (521, 535VDH). DC lot E32 617/577 and 607/586. Both AP good. Lot E33 603/463 nose good, CL poor. Lot E37 591/581 both good. Lehigh Young lot 17 638/554. Nose superior, CL good. Bethlehem lot 19A 632/568, lot 20 583/471, lot 21 453/240, lot 22 597/506. I nose superior, 2 good, 1 poor. 1 CL good, 3 poor. Chevrolet lot 3-22586-30: 625/314. Good nose, poor CL. Chevrolet also had problems with its 76 mm M62, as lot CM-3-59: 593/500, and 552/352.
When American AP tested, if a lot failed, then tested again with lowered perforation of armor plate standards, only with a second failure was the lot rejected.
German 75 Pz.Gr.39: 656/653, 649/640, 654/657, 713/717, 733/689. All lots superior nose and CL from different producers, the first PAK 40, the other three Panther APCBC.

critical mass
Posts: 87
Joined: 13 Jun 2017 14:53
Location: central Europe

Re: American and German 75 mm AP Quality

Postby critical mass » 01 Sep 2017 08:24

It would be acceptable -in practice- to use lower quality AP for lower velocity guns. Lower quality AP are charakterised to break up / start to deform at less severe impact conditions than high quality AP, and this can result in different (lower) critical velocities for a penetration.
However, at even lower velocities, the impact conditions are less severe, and consequently, the performance gap between low and highest quality AP disappears and high quality AP is not required anymore.
German Pzgr39 in the mid/late ww2 period have been developed to a higher standart of quality in regard to decremental hardness pattern and smooth hardness contour changes due to the need to respond to the generally higher muzzle velocities of their ordnance items.

The american anti tank AP shells of this period were unique in their attempt of sheath hardening instead of decremental hardening. While sheath hardening is better, particularely at oblique impact stress, it doesn´t add much for small section thicknesses of anti tank AP and really comes to shine in large naval AP designs (though here, too, the british had some measure of success with decrementally hardened naval AP).

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