They will be behind dirt for the most part. I am more concerned with ricochet then shooting through. I will have a 7 foot high wall of ties behind a huge pile of dirt. I used a skid loader to dig into the ground 4 feet below. I guess I should have asked, will a 9mm bounce off of a tie in the event I have a very off day?
I know that .38 spl. 148 gr wadcutters will bounce back. You can see them coming and hear them as they pass you. I've been hit by them several times. They only hurt when they hit me in the head or hands. Try some tires. Removed from the wheel of course. You get that slingshot effect.