Here are a couple of thoughts:
You will going to want a layered impact berm. Rock in the center, covered with dirt, then lighter dirt then sand. You will be making the "classic" inverted V shape berm. I have seen indoor ranges that use a half V. The berm pushes out on the concrete wall and causes issues down the line (like the wall separating from the rest of the building). The advantages here are that the dirt can be sprayed with water to keep the natural and lead dust down, and can be mined to remove the lead and recycled. The bullets will stay more intact than a steal or concrete backstop.
The huge drawback to the dirt berm is it takes a lot of space. I'd consider Ecology blocks that lock together like giant Legos to separate the ranges from each other. These are 2'x4'x2' and weigh 500 pounds or so. Yes, you are going to need a backhoe, forklift, tow truck etc to move them, or cast concrete between the ranges. This will give you more range area so you can make more money (I am assuming you are doing this as a for profit business). These big heavy walls should also give you a way to hang overhead baffles when the need arises.
Personally I would plan on the entire range having to become an indoor range at some point. Yes, even rifle and shotgun. The tree hugger's are coming up with some inventive ways of shutting or stopping ranges from operation. One Federal Case out of Idaho last year has a NO BLUE SKY policy, and Noise Restrictions on it.
NO BLUE SKY = You can not see any of the sky from any conscionable shooting position on the line. So they are going from an outdoor range with no baffles to being having baffles.
Noise Restrictions = The court set db levels and the number of shooters that could go through in a year. I will get this wrong it was something like 100db was 10,000 shooters a year (that is not 10,000 unique shooters, but 10,000 customers total for the year ever time a customer comes back that counts as 1 shooter), 80 db was 15,000; if they could get it to 50 dbs it was unlimited. 50dbs is very quiet, just above a whisper so that would mean it would have to be totally enclosed.
Good Luck, the US needs more ranges.