[Brick]

There is nothing wrong with using soil as your backstop. An 18" thickness will stop most cal. .30 rifle rounds, but more is better. Just make sure you build it on your property. The woods behind might be "unused" but they belong to someone. You also want your backstop to be somewhat higher than you require and your minimum thickness should be at the top. Use soil that is relatively free of large rocks since they cause ricochets.

Of course if you want you could build an indoor range in your basement, just go out through the basement wall with 18" diameter reinforced concrete pipe for what ever distance is needed to get your 10 meter, 15 yd., 50' or 25 yd. range from your firing line on the opposite side of the basement. The the soil at the end of the pipe becomes the butts and you use a clothes line set-up as a target carrier with a light or you could get fancy and end the pipe at the butt with a manhole arrangement to contain electronics for light and turning target system, ventilator and a trap to recover spent bullets to re-use as cast-your-own or to sell as scrap metal.

Good luck with the new house!