A life's (fatal) lesson on how NOT to maintain magnetos

Even so, the turrets, etc weigh a LOT. You are right, ammo is not light. And of course the bomb load

There were instances of crews with the 8th AAF who loaded up so much ammo for a mission it upset the aircraft's CG causing the plane to crash on takeoff. Pilots learned to keep a pretty close eye on that, particularly as missions went deeper into Germany.