The 50mm was abondoned (afaik) because the difficulty to hit with it. Even though it had a high velocity and pretty straight trajectory and one hell of a range (this was a former anti tank gun ya know) the low firing speed made it hard to aim with.
The main deal with it was, just like in the Me410, to take out bombers from very far away, around 1000 yards. In reality, this doesn't work. Had the pilots of WW2 had icons like we do in AH however, it would be a whole other thing. In AH this thing could waste buffs from 1.5 without much trouble (I think).
Besides, why would you need a 50mm when you have 4x30mm guns in your nose?

Edit: Only 2 262's were fitted with the 50mm gun, they were tested in combat. The "Watson Wizzers" test fired the 50mm on the ground and noticed that the recoil system was very effective as the plane hardly moved at all (which was also noticed by pilots who flew it). Same thing with the 30mm's.