My range berm is 30ft long and 12 ft high (+-). the back wall is telephone poles, when you stack them, swap them big end to little end, that way they stay level. The ends are railroad ties, with three poles in the front to stop the dirt from washing out. I only used two upright telephone poles for the back and it leaned(because of the weight of the dirt), I'd use 4 or 5 if I was going to rebuild it. By using the ploes and the ties, I got twice the amount of range and with the same amount of dirt. I added a RR-tie wall for my platerack, on the end. If you can get the dirt, the poles and the ties and a couple of helpers and a end loader, you should be able to do it all in a weekend.
I went this way, after my original dirt pile washed out during the summer rains.
If I ever rebuid it, I'll line the back and sides with old tinn roofing (or something like that) it will keep the dirt from washing out between the gaps in the poles or ties.
Good Luck & Good Shooting