>>6536129>>6536143>>6536153Only a dozen or so Bison I and II were made as they performed horribly. It was easier to tow an actual SiG.33 and you wouldn't be limited in aim.
Only a dozen or so Sturm. IIIs were made and also performed horribly. Adding a casemate limits the size of the gun, the size of the crew, ammo storage, speed, and manuverbility.
They ended up mounting the SiG.33 to a modified Pz.38(t) hull as they had a bunch lying around and could produce more, and it was reliable and easy to fix. However, this served as an SPG artillery and not an assault gun. This served until the end of the war even alongside its replacement, the Hummel.
They did end up mounting a 15cm howitzer to the Pz.IV in an armored casement (Sturm IV Brummbar), but it ran into the same problems as the Sturm.III in that the gun, equipment, and armor casement made the tank way too heavy to really be effective.
But the Germans didn't need this. They had the StuG.III. They learned that you don't need a big gun for direct support, but one that could pen and take down targets. The StuG.III could do this while still able to protect its crew in an armored casement and still be able to move quite fast. As the StuG.III evolved it became more of a "tank destroyer" than an "assault gun." (They also had similar tanks like the Hetzer.)
The Russians also branched out from the SU-122, to the SU-85 tank destroyer which had a high pen gun and high maneuverability, and the SU-152 which was more of an "assault gun." It just turned out that if you fire a 152mm shell with enough velocity, it will pretty much destroy everything. (For reference. modern tanks only use around 120mm shells and modern SPGs around 155mm shells.)
