American and German 75 mm AP Quality

Discussions on the vehicles used by the Axis forces. Hosted by Christian Ankerstjerne
Miles Krogfus
Member
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
Member
Posts: 107
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).

seppw
Member
Posts: 24
Joined: 24 Dec 2017 00:49
Location: Central Europe

Re: American and German 75 mm AP Quality

Postby seppw » 25 Dec 2017 16:43

102-7a2af963f7.jpg
You do not have the required permissions to view the files attached to this post.

User avatar
Mobius
Member
Posts: 178
Joined: 12 Jan 2005 20:45
Location: Glendale, CA

Re: American and German 75 mm AP Quality

Postby Mobius » 25 Dec 2017 17:11

seppw wrote:102-7a2af963f7.jpg

I wouldn't rely too much on Ballistics and Gunnery penetration data. They get some confirmation of their formula by looking at firing tables from AFV-G2 magazine. That in some cases mislabeled meters for yards of the Aberdeen data. (During WWII the US would not put out firing tables in meters.) In the case of the 88mm data it is just a copy of the German tables.

seppw
Member
Posts: 24
Joined: 24 Dec 2017 00:49
Location: Central Europe

Re: American and German 75 mm AP Quality

Postby seppw » 25 Dec 2017 17:18

Mobius wrote:
seppw wrote:102-7a2af963f7.jpg

I wouldn't rely too much on Ballistics and Gunnery penetration data. They get some confirmation of their formula by looking at firing tables from AFV-G2 magazine. That in some cases mislabeled meters for yards of the Aberdeen data. (During WWII the US would not put out firing tables in meters.) In the case of the 88mm data it is just a copy of the German tables.

Roger. But even if it's more than 16.6%, they still have point mentioning the "nose hardness and other factors", don't they?!
Btw, how to convert values from German 5/5 criterion to US VC50? Multiply by 1.1?

User avatar
Mobius
Member
Posts: 178
Joined: 12 Jan 2005 20:45
Location: Glendale, CA

Re: American and German 75 mm AP Quality

Postby Mobius » 25 Dec 2017 18:23

seppw wrote:Btw, how to convert values from German 5/5 criterion to US VC50? Multiply by 1.1?


Surprisingly that actually works for 50mm/L60 and 75mm/L46 guns at 30°. It normalizes armor differences as well.

seppw
Member
Posts: 24
Joined: 24 Dec 2017 00:49
Location: Central Europe

Re: American and German 75 mm AP Quality

Postby seppw » 25 Dec 2017 18:26

Mobius wrote:
seppw wrote:Btw, how to convert values from German 5/5 criterion to US VC50? Multiply by 1.1?


Surprisingly that actually works for 50mm/L60 and 75mm/L46 guns at 30°. It normalizes armor differences as well.

Is there a formular that works for all common guns? Maybe a formula depending on the diameter, impact angle and penetration?

User avatar
Mobius
Member
Posts: 178
Joined: 12 Jan 2005 20:45
Location: Glendale, CA

Re: American and German 75 mm AP Quality

Postby Mobius » 25 Dec 2017 18:47

You can try
http://navweaps.com/index_nathan/index_nathan.php
I hear HCWCALC is an improvement over M79APCLC. For me that didn't reproduce the M79 AP tables.

critical mass
Member
Posts: 107
Joined: 13 Jun 2017 14:53
Location: central Europe

Re: American and German 75 mm AP Quality

Postby critical mass » 28 Dec 2017 18:59

M79APCLC and HCWCLC are based upon Dr. Hershey´s extensive M79 database on the USNPG Dahlgren.
Hershey´s database consists of trials of the 3" uncapped, monobloc M79 AP-shot vs naval 215-250BHN homogenious STS and class B plating, normalized for ductile, 225 BHN armor grade material.
The programs algorythms are considering only one, single failure mechanism:

225 BHN grade armor ductile hole formation and INTACT projectiles.


Return to “The Ron Klages Panzer & other vehicles Section”

Who is online

Users browsing this forum: Bing [Bot], CommonCrawl [Bot]