Its 3 shots to the ass with G40 for a Puma to kill a Churchill at range, unless your close enough to hit the back deck/top armor. Trust me on this one, I had to test it for like 3 hours before a WaW battle. 50mm rounds do not register on any other part of the hull effectively.
Also, its 2 (3 at range) shots to the front of a Sherman with G40, and also 2 shots to the side to kill it with regular AP. M4A1s with the cast hull have a much higher tendency to deflect rounds if u don't aim low on the hull/tracks. So when using the Puma, G40 to the lower tracks on any tank besides the Churchill will kill it in 1 shot.
Something to note, the M4A1 76mm actually has more frontal armor then any other Sherman variant in game, and can effectively absorb 1 regular PIVH AP round (if you don't shoot the turret schurzen) while having about 2-3 bars of health left.