I have found some documentation on the ballistics of the 88mm guns as well as the 75mm Model 40 guns. Looking into the ballistics of the 75mm/L70 gun as mounted on the Panther tank it seems rather inconsistent. First of all the penetration from reliable sources seem to conflict. As we know different countries have different penetration criteria. But, there is even disagreement with German sources. Starting with data from Spielberger's Panther book. This contains a table listing impact velocity along with penetration at 90° and 60°. The book also contains a graph (Fig. 8) of the velocity vs. penetration of the 75mm/L70 gun. Unfortunately the table doesn't agree with the graph. Then there is Jentz's data as listed in Encyclopedia of German tanks. Very close to this data is the data from Fleisher's German Anti-tank Troops of World War II.
Figure 2. 75mm Pzgr. 39 penetration vs velocity
Figure 1. Datenbatten 75mm Kw K 42
Additionally the Datenbatten for the 75mm/L70 (Fig. 1) shows the penetration at 100m to be 138mm and at 1000m to be 110mm The AP projectile listed in Spielberger's book is the Pzgr. 39/42 round. This is also the type of round in Jentz and Fleisher's book. Another source I have found is the graph (Fig. 2) of Pzgr. 39 penetration from DIE VORGÄNGE BEIM BESCHUß VON PANZERPLATTEN, Lilienthalgesellschaft für Luftfahrtforschung 166 (Berlin 1943) . (This could be for all 75mm Pzgr. 39 from the L43 to L70.) The Jentz/Fleisher data is cross-referenced in the graph to determine impact velocity. The resultant numbers are listed on the table Fig. 3.
Figure 3. Range Penetration at 30° angle
Figure 4. BIOS 30° Penetration vs. Range
The fourth German source found in the post war British Intelligence Objectives Sub-committee i.e. BIOS report data (Fig 4.) This contains one graph of Penetration vs. Range for a multitude of guns. The 75mm AP44 6.8 kg. shell is listed but the muzzle velocity V0 is 935 m/s.
The penetration from the BIOS report data is then cross-reference to the BIOS report graph of Velocity vs. Penetration
Figure 5. BIOS Penetration vs. Velocity table
Figure 6. Range and Velocity table
(Fig. 5) to determine the velocity. The results of the data is compiled into table Fig. 6.
I tried to find ballistics coefficients that will satisfy the data pattern. The ballistic coefficients also had to work for the 75mm/L48, which I do have the firing table. The same Gâvre drag function that worked so well modeling the 88mm/L71 was used. The calculated results are in table Fig. 7.
Figure 7. Calculated ballistics of 75mm/L70
Figure 8 Reproduction of German Graph of 7,5 cm KwK 42 velocity vs distance.
Post war US Aberdeen data on the 75mm/L70 does record that the V0 is 935m/s. It is unclear when and what was changed. See page 48 for more references on the 75mm.