the reason a big ol dirt berm works is sheer thickness and the weight of all the dirt behind the front face, it would take unbelievable forces to push through something like a dirt burm.

that said, what you are trying to build is a containerized version of a burm, however every round you fire is going to put a hole in said container. will it stop bullets? perhaps. will it last long? no

if you can't put the dirt in the path of the bullet, then make the path of the bullet end at the dirt. or in otherwords if you can't make a burm, then get a giant piece of thick sheet steel and lay it at an angle onto some rail road ties, or logs or something, and aim within the area that creates so it knock all the bullets down and to the earth.

other than that youve basically got the options of sandbags, log piles, or if you have the money, a comercial bullet back stop for a real range in your own back yard.

The Gunners_Mate covered it well. Enjoy your prodject.You may find a "how to" from one of the search engines.

In reply to your question about will your idea stop bullets the answer is no.
It MIGHT stop a 22 but I would not hold my breath. Anything larger than that I would count on going right through all that at 60' (feet) or 30 yards.
GMs suggestion on the sheet steel is good but if you use sheet steel go thick.
Exactly how much? I would not hazard to guess. But if it were me I would want a HUGE sheet probably like a scrap hull plate from a battle ship and no less than 3/4 inches thick.
Pitched at no less than a 45 degree angle. And a good 10 foot hi. which means you need a big friggen chunk of metal.
Cheapest way to do it is probably build a large culvert with large blocks.
A nearby outdoor range divided their range bays with HUGE retainer blocks.
Each one was 3'x3'x4'. Big blocks. You could have some of those delivered and build a large three walled containment area. Wide, Deep and Tall. Then have truck loads of dirt brought in and have the containment area filled from the ground up with clean soil.
You don't want any hard objects in it that can deflect a round back or off at an odd angle. The fill dirt washing down and out would have to be pushed back up from time to time because of settling from rain.

Just a suggestion. I would talk to professionals about how to go about this for legal reasons.

I suppose this doesn't answer your question, but there is really nothing better, simpler, or cheaper than hiring a dump truck to drop a load of dirt. I regularly shoot .30-06 and other high powered rifle rounds into a single dump-truck load of dirt.

You can plant flowers or grass on it, if it's too ugly, and if you get tired of it you can spread that amount of dirt out over the yard without significantly changing the elevation, or killing the grass.

Try this, go to this forum, then scroll down to dolman jr.member and click on his link for a picture of the tire backstop he's talking about. You can't get off cheaper than used tires filled with some sort of media.Building backstop for shooting range in my backyard - Survivalist Forum

Since you don't want to pile up a dirt back stop then you might think of digging down to create a shooting lane. Dig downward until you have a 8-10 foot deep at the target then you will have a good safe back stop without the pile of dirt standing out.

Originally Posted by Frank45

Try this, go to this forum, then scroll down to dolman jr.member and click on his link for a picture of the tire backstop he's talking about. You can't get off cheaper than used tires filled with some sort of media.Building backstop for shooting range in my backyard - Survivalist Forum

Bingo.

John