@Jasonnc actually friendly fire on expert isn't 20 damage per hit, you take the full amount of damage the gun actually does. You're allowed a couple shots of friendly fire, but some guns like the sniper, auto shotgun, or even shotgun can one hit kill your teammates.
A big tip for anyone on expert is that you're going to have to strategically kill your teammates, or even sacrifice team members. This is always difficult to explain to pubbers. Killing a teammate bleeding before the safe room is always recommended, killing a teammate before you radio for rescue is always recommended if they're under 50 health. I recommend using an auto shotgun to tk, it kills really fast. As for sacrificing team members, sometimes it's a good idea to actually let a boomer blow up on one single team member. This attracts all the zombies to them and while they're getting beaten up the rest of your team just makes a break for the saferoom or next spawn area. Also tanks have a little over 10,000 hp in Expert mode, weapons are pretty useless to use against a tank and should only be used as a last resort. Make sure one person good with molotov cocktails always has one. When you hear tank music everyone except your molotov thrower should just run back the direction they came from. Chances are your tank killer will die, but it's ok just respawn him. When a tank is on fire he actually doesn't take actual HP damage but dies within a matter of time from being on fire, so shooting a Tank on fire doesn't speed up the process don't bother with it. Also if a Tank is on fire and goes into water and loses the fire effect, don't worry he's actually still on fire and will still die within a small amount of time.
