I think what matters is that there are numerous easy to make options so that everyone can make one that works for them with little to no effort. and transfer the mulch in another cardboard box when the initial box is too damaged, or tape on a new cardboard front from time to time. which means one can make one with 4 bags of 0.8 cu ft rubber mulch (7$ each) from home depot. The box is 24x16x15 or little over 3 cu.ft. Doing that with rubber mulch would be a super easy and cheap option I totally agree. I was actually going to make one of these rubber mulch trap for shooting in the backyard at 30 yards (the duct seal trap is mostly for 10m) with my 22, but I had an old area rug around so I tried that and it worked (only tool required was a utility knife to cut rug strips, and something to cut the few pieces of wood I put in the back of the folded rug strips, but that is optional). someone who does not have a jig saw can probably even get away with cutting the lid with a utility knife. What I really like about your rubber mulch pellet trap is how simple the build is. Hi Intenseaty22, I had seen the thread but not watched the video yet. 22 caliber air rifles and catches them safely in its huge internal pellet reservoir. This trap stops pellets even from high-powered. I built a pellet trap as a target back stop to contain medium velocity 4.5. if it does, then add some duct seal were pellets have punched their way through. The duct seal adheres to the back of the trap and stays in place through continued use. Iberville Compound, Asbestos Free Duct Seal, 1 Pound. 177 pellets have accumulated in the duct seal, thus increasing resistance, you should never have any pellet going through the duct seal and damage the rear backing. anything would do to protect the aluminum in the back (if you have steel go ahead and use steel). The 'sacrificial' piece of wood behind the duct seal is just 1/2' plywood. I used 15lbs of duct seal and that seems to be the right amount. This way you only have the pellets accumulating over time in the duct seal.

The way the inside shelf is done leaves a gap in front of the duct seal for the bits of paper or cardboard to fall down and be removed later from the 'slot' at the back of the trap (see picture from the back). a lot easier than measuring everything and reporting measures on wood pieces. Ask if you need any dimension but the easiest is to start by making the 'grooves' in the sides 2圆, and the bottom 2x4, and then slide an NRA target into it and mark other measurements from there. It also allows to use either standard NRA '10m rifle' targets, or any printed target on 'letter' size paper (landscape direction) by the use of 2 sliding slots. No need for a router or a mitter saw like other 'complicated build' out there. Just wanted to post pictures of the one I made as it may inspire others since it is very simple, and only requires a table saw (or a circular saw if you are good with it). I know this 'duct seal' trap idea is not new and many have done it already.

Duct seal putty pellet trap