Ceraphix, besides the technical problems T.A.Gardner mentioned, there is also the fact that Soviet tanks were not to be specialised tank-killers, they needed a decent HE capability, and the 57mm shell was too small for the purpose.

So good as the 57mm gun was, it was difficult to manufacture in large numbers, needed development, and the explosive round was considered small for general pupose work.

Kriegfilms, 2" is not exactly thin skinned if you take into consideration the very oblique sloped armour.

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