It's not so much how
much land you have as how it's laid out. I'm on ~7 acres. I only need ~4 of that acreage to include the house and the rifle range. My parcel is rectangular, 115yd x 300yd, but the house is damn near in the middle; I don't really need any to one side--I needed the long 300yd strip to hide the 200yd rifle range.
Here, the law says I can't shoot any closer than 300 feet from my neighbor's dwelling/building; closest neighbor downrange is about 1800yd away at 45 degrees from the firing position. (I investigated all this before I closed escrow.)
As I recall, the NRA recommends a berm that's 15' high. Mine is about 13', and all my targets are about 8" off the ground with a 3-foot thick, 4-foot high, "compound", vertical, log fence backstop in front of the berm (I'm probably the only one to say "thank you, Katrina"
for all those big trunks and limbs (stacked on ends). Any ricochets will go left and right). I'm glad the berm is 13' high; there was a time when I thought the trees behind the berm would render the berm's height unnecessary, but Katrina thinned that out too much. The berm at 13' works very well; for the pistol targets I use only steel plates angled to direct ricochets into the dirt directly in front of them. For my rifle target, I built a box in front of the berm 4' x 4' x 4' and filled it with sand. As backing for the bullseyes, I nailed 1" rubber gym padding to the box's wooden wall; that keeps the sand from spewing out as the bullseye's hole in the wooden wall gets bigger. Sometimes I'll wet down the sand so it won't leak out as easily.