I am planning on using railroad ties for backstop . Total height to be 10 feet high and 16 feet wide with 2 side 8 foot returns. Ill interlock the ties and stake them. Ill completely fill the resulting c shaped backstop with compacted fill. 8 feet at bottom and slope to top ...as thick at the top as will stay in place.
Going overkill as safe rather than sorry. the max distance will be 80 feet to target, and who knows what caliber of guns well be using in the future. I was going to skip the wood backstop, but in order to build it 10' tall x 16' wide, the sloped sides would be massive. Overall this way will result in a smaller overall mound. Should disappear rather nicely.
The 275' rifle range will incorperate an existing cleared arena with a deep cut wall that already exists. Its alreadt 6' high cut wall . Ill add more to the top to bring it to 10' also.