In the 1942 report on trials of captured, domestic, and Lend-Lease vehicles (CAMD RF 38-11355-832), which you should all be familiar with by now, a number of such tests are described.
First, the LT vz 38, or PzKpfw 38(t), shoots at the StuG III.
At 100 meters, the 37 mm shell makes a 40 mm dent, but does not penetrate. At 50 mm, the formed is the same depth. Another shot from 50 meters, this time with an uncapped shell, makes a dent only 22 mm deep. Firing at the side from 850 meters, the Pz38(t) penetrates 3 times in a row. The diameter of the hole is 40 mm, which indicates ductile armour.
Subcaliber shells are loaded. From the same 850 meters, the shell hits a 10 mm screen, and breaks up. The main 30 mm armour plate has "an insignificant scratch" on it. Firing at the 30 mm armour with no screen, the shell fails to penetrate again. The core got stuck in the armour plate. Closing in to 400 meters, and firing at the screened armour, the shell only manages to make a 2 mm dent in the main armour plate.
The Pz38(t) starts firing at the front again. From 100, 200, and 400 meters, the subcaliber shell penetrates the front of the StuG. The diameters of the hole range from 15-18 mm.
Conclusions: "The 37 mm armour piercing shell does not penetrate the front 50 mm plate from any distance. The 37 mm armour piercing shell penetrates the side 30 mm plate from 850 meters. The subcaliber 37 mm shell penetrates the front from 400 meters. The subcaliber shell does not penetrate the 30 mm side armour."
Next is another captured and re-captured tank, the S35 Somua. Its 47 mm gun faces off against a StuG.
At 100 meters, it penetrates the front. Same at 250 meters. The diameter of the holes ranges from 45-55 mm. Another shot at 250 meters does not penetrate the front, but makes a 45 mm dent. Inside, an armour fragment equal to the shell caliber was knocked out. At 400 meters, the Somua penetrates once (next to the armour plate edge) and bounces off once, after making a 25 mm dent.
Conclusions: "The 47 mm AP shell penetrates the front from up to 300 meters."
Finally, we have two honest Germans facing off: a PzIII firing at a StuG.
At 100 meters, the shell penetrates. Hole diameter is 80 mm at the entrance, 60 mm at the exit. At 250 meters, the result is the same, with 50 mm on entrance, and 45 mm on exit. At 400 meters: 60 mm and 55 mm. Another shot from 400 meters penetrates the lower armour plate. At 700 meters, the shell penetrates the front of the StuG three times, with entrance diameters of 55 mm and exit diameters of 50-60 mm. At 800 meters, the shell penetrates the front plate, and gets stuck. An armour fragment 200 mm in diameter is knocked off on the inside
Conclusions: "The 50 mm armour piercing shell, fired from the 50 mm gun on the PzIII penetrates the 50 mm armour of a StuG at 800 meters."
In this test, you can also see that the StuG's ductile armour starts spalling once hit with a lot of kinetic energy, even if it doesn't crack like the Pz38(t) did previously.
That's it for the guns tested. The conclusions describe the shell condition after impact:
"The 37 mm German shell for the Czechoslovak 37 mm gun makes a 40 mm dent in a 50 mm armour plate at 50 meters. Without a ballistic cap, it makes a dent of 22 mm. Either way, the shell is fully destroyed.
The 47 mm German shell for the 47 mm French gun penetrates 50 mm of armour from 100 and 250 meters. The shell is not destroyed. The tip of the shell, in most cases, retains its shape.
The 50 mm German shell for the 50 mm German gun penetrates 50 mm of armour from 100 meters to 800 meters. The shell is not destroyed."
Next, let's take a look at the bigger German guns, fighting bigger German tanks. First up is the PaK 43, against a Tiger II.
"Shot #21. Target: upper front plate. Distance: 400 m. Dent 360 mm by 130 mm, 90 mm deep. A 510 mm by 160 mm fragment of armour was knocked out on the inside. A 1700 mm crack formed through the existing breaches.
Shot # 23. Target: front of the turret. Distance: 400 m. The shell hit the gun sight opening. Penetration, 130 mm by 110 mm entrance, 110 mm by 90 mm exit. 150 mm by 115 mm fragment is torn off the armour. The shell exploded behind the armour.
Shot #24. Target: front of the turret. Distance: 400 m. The shell struck the side of an existing breach. A hole was formed 100 mm in radius at the entrance. 270 mm by 220 mm, 130 mm thick, fragment of armour broke off on the inside. The welding seams on the gun mount ruptured, and the gun mount flew off.
Shot #25. Target: front of turret. Distance: 400 m. The shot made an entrance breach 140 mm by 170 mm, breaking off a 40 mm by 190 mm, 35 mm deep, fragment off the rear side. The rear of the turret has a hole 70 mm by 90 mm. The following welding seams burst: left turret side and turret rear, 600 mm in length, left turret side and turret roof, 950 mm in length, turret rear and turret roof, 450 mm in length, left side of the turret and turret roof (close to front), 500 mm in length, turret front and turret roof, 800 mm in length, turret front and left turret side, 200 mm in length."
The Tiger II's own gun (the KwK 43 was just a PaK 43 in a tank) seems to have trouble with the upper glacis, but spalling finishes the job, as always. The turret, however, is easily penetrated at 400 meters.
Next is the KwK 42, firing at the same Tiger II.
"Shots #26 and 27. Ricochet from the upper front plate into the turret.
Shot #28. Target: upper front plate. Distance: 100 m. The shot hit an area weakened by previous hits. A dent 280 mm by 110 mm was formed, 80 mm deep. As a result of cracks caused by previous shots, a 1500 by 1700 fragment of the hull fell off."