Beware of the crossties. I had a pistol range for several years and used cross ties as a backstop. I had to add a hanging curtain of carpet in front of it due to bounce-backs. The bullets would penetrate the carpet going forward but couldn't when coming back. Granted, before I added the carpet, there were only two bounce-backs out of many thousands of rounds fired and both were 45 cal fmj but the second hit me in the knee and that was one too many.
Use dirt or buy a bullet trap.
IDPA Member A00640
Founding Charter Member - Middle Tennessee Shooter's Club