On the tanks encyclopedia website, it lists all the types and variants of pretty much every tank. in the M4 section it goes through all the Sherman variants and modifications. It lists two 75mm variants for each successive model, stating there was an improved, longer-barreled 75mm gun used on later upgraded models. Was there an improved, longer 75mm gun used on the later Shermans? Also, was the gun on the M3 Lee different than the gun on the M4? It looks shorter form all pictures I've seen.