Wood mulch as a backstop.

I would be concerned that wood mulch might decompose or settle unevenly, perhaps leaving voids.

A decade or so back I tried to make do with a stack of railroad ties that were bundled 8 deep and 8 across.
All that I shot was handguns,they fell apart in less than a year and made a huge mess.
If you can find shredded tires,that are safe to handle [ steel mesh is very dangerous to handle ] and you fill that space with the tires,your closer to a real backstop.
Take a hard look at a "shoot house" that is constructed of tires that are then stacked and filled in.

I would not use wood mulch.

Sand is best, and easiest to mine for recycleing the lead.

don't use it i seen 22lr's go through 10 feet wide piles of mulch.

I would only use sand. Wood mulch is not at all dense. More than once I'd had it float away on me after a torrential rain.

Am I reading your dimensions correctly that you're going to go eight feet deep with it?

Don't use anything organic. It will decompose, and is not all that dense. Sand is best.

Sand is the ticket

I built a handgun range behind my shop that I use for the shooting qualification portion of CPL classes I teach. Site was pretty level with no natural backstop so I had 30 yards of sand trucked in. Behind it is an open field with several acres of trees on the other side. When it starts sagging from the weather I buck it up with my loader. This has worked out well for me.

Our club used tires filled with sand stacked in a brick pattern/pyramid as a back stop.
No pics but it looked kinda like these, except more free standing, not built as a retaining wall, wide at the bottom:
https://www.pinterest.com/search/pins/?q=tire and soil retaining wall&rs=typed&term_meta[]=tire and soil retaining wall|typed

I don't think you need to be so elaborate. Just get a guy with a bulldozer and excavator to make a dirt berm about 5 feet high and 10 to 15 feet long.

Mulch is actually designed to decompose into (much less volume of) dirt, so no.

Sand for fillers if you must have structural walls. As mentioned, railroad ties are good for backup, but not for regular impact zone. Only make RR tie walls if there's something in front to absorb most impacts.

If you have the room, dirt berm. And, monitor it, as it'll erode and need to be rebuilt every few years. If you don't have the equipment, you'll be hiring someone to come over with the bulldozer for that.

My dirt berm needs a little work about once every 7 or 8 years. It holds up pretty well.

A buddy of mine had a range put in when he was building his house. Used fill dirt for the berm and stacked bags of sand in front of the dirt.

I hung some steel in old tractor tires....you should see the splatter in the rubber.

My buddy and his dad built something years ago and took RR ties 2 deep with solid cinder blocks behind it and sand and dirt dumped behind that. I don't think the cinder blocks are a good idea because it makes a mess and sends fragments of concrete everywhere. The RR ties and sand/dirt was good but RR ties need replaced every year or so.

A friend built one using tires filled with dirt that is over 6' tall staggered like a brick wall, we used rebar driven into the group to help the first couple of rows.
I helped him make some frames for 1/2in steel and at 100yrds we've never had a problem. You could build it more than 1 row thick to improve the stability, this one is about 5yrs old. I've not noticed anything going through, the heaviest I've seen shot was 30-06 or 8mm Mauser.
He picked up the tires from a local independent tire store he uses for free

Our range uses railroad ties backed by 10 feet of sand. The ties get replaced every couple years. Use sand.

Tilos said:

Our club used tires filled with sand stacked in a brick pattern/pyramid as a back stop.
No pics but it looked kinda like these, except more free standing, not built as a retaining wall, wide at the bottom:
https://www.pinterest.com/search/pins/?q=tire and soil retaining wall&rs=typed&term_meta[]=tire and soil retaining wall|typed

Click to expand...

Do you not get ricochets from small light bullets like .22lr with the tires?

I used to belong to a small club in north central Florida. It was one area with benches at 100 yards; if you wanted to shoot closer (like pistols) then you moved closer. The backstop was an old WWII backstop previously used by the Army Air Corp where they tested and timed the 50 cal machine guns on the B-24s. It seems that area was once an AAC airfield (as was much of Florida then).
This thing has tie downs (still visible) where they would chain the planes down and start the engines as they fired the 50s. This backstop was three sides of thick concrete running 20' high -with hundreds, if not thousands of cy of dirt. It has a ceiling of 12x12 oak beams across it. massive to say the least and nothing ever ricocheted over or around it. THAT would be my concern with any home range - things leaving the property and exposing you to massive liability

Clean sand is the best, and in most cases, the cheapest berm material. Cheap wood chips piled high/deep will compost if allowed to get wet and because of this, may smell, Clean dirt(this means no rocks larger than your thumbnail works just as well. You don't need a wall behind it unless you want to. Many folks I know use a tarp over the top and back of their berms to help with erosion. Doesn't interfere with the shooting side and also helps keep the weeds down. Burying tires is illegal in many areas because of safety and health concerns. In many areas where frost occurs, the tires will work their way to the surface in short order and look like heck.

George P said:

Do you not get ricochets from small light bullets like .22lr with the tires?

Click to expand...

I could see old tires bouncing...AG or industrial tires...some are quite hard to start with

I built a cup shaped wall of RR ties laid up like a split rail fence a little over 6 feet high. Screwed to the front surface of the ties is corrugated plastic sheets. Two dump truck loads of yellow sand were dumped in front of that wall. At the 6 ft. level the sand is probably 14" thick and 6 ft. wide. There are 2 ties across the front to help keep the sand in place. About 2 ft. above ground level the sand is 5 ft. to 6 ft. thick behind the targets. This was built in 1972 and about 5 years ago I replaced the 2 ties in front and slightly re-positioned the sand behind them. Recovering bullets on a few occasions, the deepest I have had to dig is elbow deep to find pure lead bullets from 45 and 50 caliber muzzle loaders. Jacketed bullets may go 8 to 10 inches deep.

I use a backstop made of 2x8s, plywood and a horse stall mat, filled with sand.

I haven't shot any high powered rifle rounds but its stopped all my pistols and 12g shotgun slugs.

Sand is the way to go! On the internet look up Ballistic Sand used by Tri-County Gun Club in Oregon. Ballistic Sand is none other than No. 10 ODOT approved gravel used as the aggregate in asphalt road paving. This is probably used in every state. Also on the internet look up sand absorbs high-speed ballistics impact better than steel by ScienceDaily.