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My guess would be that they are testing in the desert, and the Germans may not have made a 'Fur Tropen' round for the short gun. The reason being the gun could take it. Look at its HE round, it has a higher muzzle velocity than the AP.

I guess the Germans put 7,5 cm Pzgr 39 on the short gun's ammo also?

I know at altitude, things fly better (thin air). I am not so sure about the low level desert air. I would assume they are using British test plate?

The data is a little odd. The normalized data (red line) of all other data for the 75mm APC doesn't carry as well the O.B. data for the same round (green line.)

British Armor? British penetration definitions?

Does the other OB values seem inline?

ORIGINAL: Elron Hubbub

British Armor? British penetration definitions?

Does the other OB values seem inline?

The L48 does seem to follow the Aberdeen path.

The 2400f/s data is in blue all other 75mm/L48 are red data. Two red sets are almost the same and they are from Aberdeen and what may be British data.

(It gave me an opportunity to improve my data averaging and normalizing program.)

Pak 40 MV 2600 f/s (792.48 m/s)? I assume you meant Pak 40?

Oops sorry, I corrected it. It is the first one on the list, 2400 f/s. KwK 40

Here's another graph of different data collections and subsets.
The red line is the average of all the 75mmL48 data points. About half are German and half are British. They are from different sources though there probably are duplicates as who can tell what an author uses?

The blue line is raw Aberdeen data. But I don't know if Aberdeen did their own testing or worked with the British. The pink line is the same data but normalized.

The green line is the 2400 f/s O.B. data. It seems to be similar to normalized Aberdeen data. It also doesn't track with other British data of the red collection.

O.B./43/CV.12 May 25,1943
shows for 2400 f/s muzzle velocity (731.52 m/s) of 14.81 lb. APCBC shell ("MV as tested by trial in KwK 40") at 0 and 30 degrees deflection:
2400 f/s penetration 121/102 mm,
2000 f/s (609.6 m/s) 98/83 mm,
1600 f/s (487.68 m/s) 75/63 mm.

Given the date, I would almost have to think this is a L43 gun. If it was a StuG, it might be a L48, but the KWK 40 (Panzer IV) held onto the L43 longer.

ORIGINAL: Elron Hubbub
Given the date, I would almost have to think this is a L43 gun. If it was a StuG, it might be a L48, but the KWK 40 (Panzer IV) held onto the L43 longer.

2400 f/s is only MV of 732m/s so it's probable. I'll have to see how it compares with other L43 data.

It does show that the Pzgr. 39 was out before Kursk. What the Russians were testing after Kursk to get low penetration numbers is confounding.

Here is how the 2400 f/s O.B. values compare to other 75mm/L43 data.
Seems a little high.


And then I found this War Office memo.

WO 185/178, Tank armament versus armour 1943
"Thickness of armour penetrated by 80% of projectiles striking the plate at an angle of 30º to the
normal":
----------------------------MV armor 500 yds 1000 yds 1500 yds
7.5 cm KWK 40 APCBC 2400 MQ 89 79 62

The 80% number seems like something the Russians were doing with their certified penetration criteria.

A memo from the Ministry of Supply dated 1st April 1943 gives the following figures for "Single homo
plate penetration at 30º in mm."
------------------500--1000--1500--2000
7.5cm KwK40 APCBC 89 79 70 62

Top graph.
I had a 1943 Aberdeen graph but did not post yet as it has some parts missing. I filled them in and found that this must have been the graph the O.B. used to make their table. This has different ballistics for the KwK 40 than the 1945 Aberdeen table (post #213). The graph of 1943 shows the KwK having a ballistics coefficient of only 1.929. The 1945 graph has different 75mm KwK/PaK 40 guns having better coefficients ranging from 2.241-2.353. This looks like further testing gave the guns less loss of velocity and longer range penetration than originally thought in 1943.

O.B./43/CV.12 May 25,1943
shows for 2400 f/s muzzle velocity (731.52 m/s) of 14.81 lb. APCBC shell ("MV as tested by trial in KwK 40") at 0 and 30 degrees deflection:
2400 f/s penetration 121/102 mm,
2000 f/s (609.6 m/s) 98/83 mm,
1600 f/s (487.68 m/s) 75/63 mm.

Based on this graph 2000 f/s is at 975 yds and 1600 f/s is at 2087 yds.


Bottom graph.
Using the ballistics per the 1943 Aberdeen table I compared the O.B. 2400 f/s data (blue) to the 75mm/L43 all sources data collection (red) and it falls almost exactly along the average of the data. (The data collection does include the earlier not so good data with later data.)

I've called these graphs 'Aberdeen' graphs because the 1945 graph matches the Aberdeen table data and uses the 50% perforation criteria (US Naval Ballistics standard) but I don't know who actually produced them They have the style of some British graphs and have reference to some O.B number. And the dates are in the European style. Maybe UK and US jointly?