There is a large category of fans of alternative history who like to install large guns into small tanks. These people don't exist only on the internet, but also among popular authors of quasi-historical publications. They sometimes even provide some kind of schematics and make grandiose projections. While modern plans have little to do with reality, tank designers many years ago worked towards very similar goals. Every army wanted to put a larger gun into its tanks. This typically happened as a result of increased requirements for tank guns. This process started very early in the USSR. The MS-1, the first Soviet mass produced tank, was built with a 37 mm Hotchkiss gun. This was far from the only weapon proposed for it. The same gun mount could have been a home for a "high power 37 mm gun" or "37 mm Rheinmetall gun". There were many cases where the proposed gun would simply not have fit into the fighting compartment. For instance, this was the case with the AT-1. The 76 mm PS-3 gun failed to enter production and took down the SPG with it. Other 76 mm guns (for instance the L-10) wouldn't fit.
|The 85 mm AA gun was seen as a potential anti-tank weapon and tank gun back in the summer of 1940.
|Draft of an 85 mm ZIK-1 gun in a T-34 tank, April 1942.
|The barrel was shortened to 40 calibers.
|This photo illustrates how well an 85 mm round would fit into the T-34 turret. Consider that the DT magazine racks are not installed.
|T-34 tank with an 85 mm S-53 gun, December 1943
|The mantlet of the S-53 was better than the one of the D-5T and LB-1.
|Opinions about the crew conditions at the Gorohovets ANIOP.
|Trials of the LB-1 (ZIS-100) in the stock T-34-85 turret.
|The results were similar to what happened with 85 mm guns in the T-34.
|Both the size and weight of the round have an impact.