I live in a CA neighborhood where homes are close together. NextDoor.com could be described as a cult media center for the abused in the area. If anything is slightly askew the sheriff may show at your door and your name will be disparaged and broadcast to about 1 million people. Safety and sound are critical to me or my shooting days will be limited. Therefore, I'm a bit over the top on both, maybe one of these ideas helps someone out.
I own the Highwild 11x11 "22 rimfire rated" bullet trap about 18 months ago ($53). I found it was too small at 11x11, which is a bit of a white lie, the target sheets are 10x10, it's loud, and doesn't collect and retain all the lead. I was constantly sweeping up the concrete around the unit, But still it is a solid unit and for $53 is a killer bargain if you're on a limited budget. But to me size matters, I want to be able to move around a larger target area to reduce boredom. I wanted to reduce the number of times I have to walk up and add more splash circles covering the old splash targets. I wanted a unit that reduces sound and is better for the environment. Therefore I purchased the Super Target Systems 16 x16 x 8 (47lb) bullet trap, $210 delivered, rated 22 long rifle, and gave it a try.
Assembly was fairly easy, with no help. Instructions are garbage so I studied the on-line pictures as my guide. I went to Home Depot and picked up a bag of Vigro rubber mulch for $8 and the unit consumed the entire 22.2 lb bag. Fully loaded the STS unit weighs in at 70 lbs to the Highwild's 16 lbs, enough said.
I put the STS unit on this cart which I highly recommend (rated for 300lbs) and purchased a barbecue cover. I'll leave it out in the weather and when people are around I want to hide it.
WEN 73162 Two-Tray 300-Pound Capacity Double Decker Service and Utility Cart
When you first see the STS, lift and feel the ballistic rubber faceplate you wonder "will my pellets penetrate this 1 inch thick sucker?" It is a very solid and somewhat imposing faceplate, but my pellets made it through it and every single pellet was captured internally, about 100 shots. That's not the case with my Highwild.
I started with my HW 44 22 cal., no problem penetrating the faceplate. Moved to my Notos 22, again no problem, then finished up my day 1 test with my GK1 22 cal. The picture shows the GK hits result, all fired from 50 feet. You can see the sound level from the attached pic of my meter that was placed about 5" in front and to the right of the face, 79.1 DB. It was the loudest reading of 38 shots from GK1. This unit vacuums up every shot if you hit the on the full 16x 16 face, impressive
I shoot down a stone wall canyon to a open air, metal gate. For a backstop I followed the Colonel's program, terrific video;
I hung 6 mm 3x5 polycarbonate sheet that should stop a 22 live ammo rimfire round according to Tom, covered it with a up with a throw rug. Then I installed a 3" x 5" sheet of Xtreme Sight Line ~ 1680 Denier Ballistic Nylon $20. Barring a stroke, no pellet is getting outside my yard. I also believe if 2 double pieces of that material were overlapped, with another section of 2 over-lapped pieces side by side for 6' x 5" coverage, and were hung on a portable clothesline, you would have an outstanding low caliber backstop, cheap and portable. That "1680 ballistic" is tough stuff.
Lastly, I created a firing canopy which is hillbilly, but it works. I bought 3 sheets of 18x24 polycarbonate, installed an inner lining of acoustic material, lashed them together with industrial hinges from home depot, covered the top with a dog bed and a beach towel to hold the dog bed down. See pic. It's a large tunnel to fire down that blocks sound, I hardly notice it anymore. I break out the sound meter and place it about 4 feet away outside the box everytime I shoot. Only the GK1 with a Neil C. moderator breaks 75 DBs, it's usually around 77, very acceptable. Ya we can debate if those DB readings are BS or a defective unit, I don't care, I feel the canopy reduces my exposure. My 25 cal GK will be here later this month along with an Impulse 1350, I'll get back to you. It's like I told my neighbor immediately to the right of me. If the sheriff shows at my door I want to invite them in my yard to "show off" my r range.