Well my shooting range (a hay field) is no longer usable due to change in seasons, my next best spot would be using a big pile of old tires as a back stop (not stacked, just dumped there). theres nothing but corn field (no houses or anything) behind the tires for about 1/2-1 mile. So i guess what i'm wondering is will a pile of tires saftely stop a bullet?

Drive a pipe or 4x4 post into the ground then place the tires over the post. Fill each tire with dirt or sand and stack as many of them as you think you need. Keep the post or pipe to the back of the tire. You will be surprised how deep the bullets will go into the tire. You can also make the back stop a lot higher that way. If you are worried about them making it through one sand/dirt/gravel filled tire then put a second set behind the first. You will sooner or later shoot out the tire. All you do then is pull the damaged one and replace it. The bullets will pass through but the tires will close back up and hold the dirt and sand.

Since you have the tires and probably a shovel you have a free back stop. It will also catch your lead that you can recover. This can be melted back down and you can cast bullets from it if you clean the lead.

I done this with a tire and then have a steel backstop just to catch the lead that might blow through. I finally shot the tire out.... so I filled the trap with gravel and am still shooting...