I haven't seen this and I even searched for it seeming that I couldn't be the only one who has thought of this so far. I think when you are using the shotgun that if a zombie is close to you, you should have to shove the zombie away before shooting. The sawed off and pistol can still be used to kill zombies in close combat, this seems realistic. I can't imagine having a zombie in my face and still be able to use the shotgun effectively. On the same note, when you run out of ammo with a weapon, you should be able to shove zombies away. I had to reload my shotgun today, but needed to shove a zombie off of me first. By the time I figured I couldn't shove a zombie while having a shooting weapon equipped, it was too late and I was eaten. Not that I care that I died - I mean don't we all in the end - but I thought it was weird that this wasn't a feature with ranged weapons, but is already a feature with melee weapons.