You don't need/want sandbags .... you need a bulldozer.
Exactly. My range, built of dirt on my property with a bulldozer. It a little hard to see the berm behind the wall now since it's somewhat overgrown. This is good, it holds the dirt in place. It is approx. 9'-10' tall and 8-9' deep x 24' wide at the top. Maybe 25' deep at bottom. It took a very good man about 1/2 day to build the berm. Behind it is empy forrest for over a mile. Nearest neighbor is around 700' beside/behind. I use the range average 2-3 times / month for 2-3 hours. Distance from the shed to the wall is 75 yds. Gongs are 3/8" plate, impervious to lead pistol rds., standard .30 rifle ball (Garand) will bore right through them. I have to re-build the central part of the walls once / year or so, not a big problem.
There is a risk. It's tiny and I'm willing to risk it. I would have to miss the entire berm and have someone in the line of fire - the odds of both happening at the same instant are miniscule, but not zero. Ricochets off a vertical wall or plates are quite easy to stop. Life is risk, you mitigate what you can. Total cost, including the shed was around $3,000 iirc. Worth every cent.
Someday someone may buy the land behind before I can get it and build, and that will be the end of it, but for the last 10 years I've had it pretty good.
Know your local laws - firearms, discharge, noise, nuisance, etc.
Know the area - Google Earth is invaluable here, if the resolution for your area is good.
Forget the tires, sandbags, other gimmicks. Build it with a bulldozer.
The wall is optional, but it sure is nice and holds the front of the berm in place and makes it easy to hang gongs, targets, and so on.
FWIW - I think it will become nearly impossible to enjoy the shooting sports anywhere in the country over the next generation, and there is nothing we can do about it. I hope I'm wrong.
Don't give up - form clubs, buy land, get involved politically, be responsible, admit the simple fact that firearms are in a danger-to-others v. benefit-to-society class all their own. We have to deal with that reality responsibly or we will lose all rights to them.