I live in the mountains of WNC. My berms were mostly dug out of the side of a hill. However, in some places,,, where we were going below the hillside I was on,, we used the dirt we dug out of one bay, to build up berms for a different bay. I have 7 pistol bays, and my range is build kinda going sideways into a hillside. Some is dug out, & some is fill in.
Build berms at an angle to allow for settling & drainage if possible. In my place,,, due to space & such,,, I've built several RR crosstie walls to hold back the dirt from washing down. Plus, I still get dirt falling & sliding down. In fact,,, we'll be digging & moving dirt this week.