Okay so, the damage it does in zombies (to the chest) is 20, so you would need 7 shots to the chest to kill a zombie on round one.
George has 250,000 health (and an additional 250,000 for each player), so if you shot him in the chest, theoretically it would take 12,500 M1911 bullets to kill him in solo, and 12,500 bullets more for each other player.
Obviously it would be significantly less if they were all headshots (6,250 bullets, which gives a 2.0 damage multiplier)
George's health/20(insert damage multiplier here) = amount of bullets needed to kill him
eg, 250,000/20(2)= 6250
So with a combined amount of headshots and body shots, it could take anywhere from 6,250 to 12,500 bullets to kill George, implying you hit him every single time.