Duct seal pellet trap vs rubber mulch?

I use a cardboard box to hold rubber mulch. At least 2” deep for every 10fpe should be fine for indoor shooting. Mine is 4” and I use it to chrony my 20fpe FT rifle at PBR.
I filled mine up and shook it to get the mulch to pack and settle and then added more as needed. Every so often I flip the box over so I don’t create a cavity where I have repeated shot impacts. When the cardboard face gets shot up, i don’t replace the box, I simply patch the box with another piece of cardboard and tape. The cardboard pieces I get with pellets ordered from PA are great.




 
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Pressed alfalfa bail, put it in a cardboard box to keep hay from getting all over. Stops them holds them no mess perfect size easy to attach targets for $17 . There's thousands of pellets in mine. Someday I'll cut it open and screen the lead.

A .22 rimfire will not go through it.tested it this way before bringing one inside. 
 
Better is kind of subjective here. Both Duct seal and rubber mulch targets are good for indoor or outdoor shooting. Both have their pluses an pitfalls as well. As you have noticed the duct seal can be difficult to clean but does not need cleaned all that often. Still it is the best as size per fpe it will absorb by far. Two inches of Duct seal will stop a hundred fpe 9mm so it is pretty stout stuff and the trap can be rather small. A few of those hundred fpe 9mm shots did split my oak trap at the rear though.

The rubber mulch will also stop powerful projectiles but it takes up allot more room. At a couple to several inches per ten fpe it's going to have to be a large trap. It also smells, well like rubber, if that does not put one off it's a great trap as well. It also needs topped off with new mulch now and then and is messy to clean when it needs it.




 
I use a cardboard box from my favorite beer 12 bottle container, filled with junk catalogs that come in the mail daily. By the time it's shot up and ready to discard, I have the next one full. I tape two opposing sides with duct tape, just to hold everything firmly. The pellets don't go half through, so it's reversible. I have no idea how many shots I typically put in it, but it's a lot. I use targets with multiple aiming points, so the shooting is distributed over most of the box area. If an area gets too shop up, another layer of duct tape will hold it a while longer. It will finally bulge out a bit so that the surface is no longer flat, time to throw away. Great use for junk mail.
 
I have made a bunch of targets. 1/4" steel boxe filled with rubber on wheels. several stationary duct seal targets. One stays on a shelf in the laundry room for pistol. Cardboard boxes with old clothes. Plastic Cat litter container filled with rubber mulch and it has its own handle. And about 10 stationary steel targets scattered throughout the property. What I use most is what is easier at the time. The boxes of clothes are FREE and the plastic 5lb cat litter is garbage. These get used the most. And I leave the box on one of my Dollys, even though the box is light the dolly is quick and easy to wheel to different marked ranges. Bur I must confess to having somewhat of a redneck mentality. I dont need nothing fancy y'all