I have a 100 yard range behind my house. I constructed my berm using my John Deere tractor with front end loader. I piled the dirt app 10 feet high with it. I have tuned it back up twice over the years. It is probably a good plan to get dirt from some location not directly infront of the berm if possible. Using dirt from infront you will end up with a muddy mess if you are not careful.
If you have a location on your property not a great distance from your planned berm location ( within say 200 feet), a Track Loader can build you a pretty good berm in a couple hours.