We use a 60" x ~8' Sheet of 1/2" A36 steel angled at 45 degrees into a bed of sand. It is placed inside a wood structure to protect from the weather. We installed some 1/8" steel splatter shields on the sides of the main sheet of steel to protect the wood against the bullet splatter. The back of the structure is an 8'x8'x2' thick box of sand. We built a roof over the structure to keep out the elements and we have range storage behind the sheet steel to keep targets and such. We only use the range for pistols and 22 rifles the range has held up really well.
With my Dad being retired he usually is building "toys" for the range. It has come a long way since we first went the sandbag route. It is starting to look like a shooting carnival.