I just thought it would be realistic if certain caliber bullets could actually clear through certain materials. A lot of people are comfortable taking cover behind a wooden door, but in real life a .30 caliber round or 12 gauge slug could clear through the door. This would play a serious role in gun safety. Too many players are comfortable with the notion that mailboxes, cars, and wood boards are bullet proof. While some rounds are incapable of going straight through certain obstacles that is a very small collection of calibers. A .22 is known to skip and ricochet off the surface of water and is considered lethal up to a mile and a half. (Of course naturally that all depends on bullet drop and how much energy it still retains at that range. But it is still considered dangerous by many and it's the smallest rimfire cartridge in existence. I'm just suggesting that the realism of the physics play an important role and you should really have to watch where you're pointing your weapon, if zombies are in front of boarded up house and the possibility of survivors inside exist, would you risk taking a shot and having it go through that zombie or completely miss and going through their wood boards, door or walls and potentially killing another player?