A backstop for decelerating and trapping projectiles generally includes a support structure having an inclined surface and a projectile trapping medium disposed on the inclined surface. The projectile trapping medium may be either a resilient granular ballistic medium or a combination of a ballistic medium with a hydrated super absorbent polymer (SAP) gel. Preferably, the support structure is made of a shock absorbing, foamed, fiber-reinforced concrete, such as SACON®. In embodiments, the support structure also includes an enclosure. Additives may also be mixed into the projectile trapping medium to control alkalinity and prevent leaching of heavy metals.