Same here. I'm kind of a belt and suspenders guy, so I double up on the cardboard. Allow me to explain in sort of a step-by-step fashion. Like a lot of folks, I used large plastic tubs for my rubber mulch filled pellet traps. I got a specially-priced three-pack, so for each trap, I
- Cut out a rectangular hole (just a smidge smaller than the size of the bottom of the tub) into the lid, so I can
- Put the targets in that space and shoot into the mulch to stop the pellets. To keep the mulch inside, I
- Open the top and lay a couple-three sheets of cardboard (cut larger than the hole in the lid) on top of the mulch nuggets. Simply
- Close up the lid, then
- Glue, tape or otherwise secure a cardboard sheet into the lid opening, on which I've previously applied as many rows and columns of two-inch adhesive Shoot-N-See targets as will fit. Now,
- Shoot 'em up!
No need to worry about mulch coming out through shot-up cardboard. Yes, pellets make tiny holes as they pass through the cardboard sheets without difficulty, but damage to the cardboard from my .177 and .22 caliber groups of as many as 10 shots on each target (I usually do three to five-shot groups) isn't enough to allow the chunks of mulch inside to spill through.
I try to make up a bunch of these sheets beforehand, typically while doing something like spazzin' out on brainless TV, so everything is ready as needed. The cardboard basically is free: I get it from the shipping boxes in which the junk we order online is delivered. Every time we get something new, we unpack the box and I get the empties, which I cut into the largest pieces of cardboard possible and keep under the side table beside my easy chair. When I feel like it, I grab my cutting board, straight edge and box cutter and cut and paste the larger rough-cut cardboard sheets into the two specific sizes needed: the larger sheets that keep the mulch inside the box and the smaller sheets cut to fit the hole in the lid. Then, on the smaller sheets, I apply the self-adhesive reactive targets (as many as will fit). When I've had enough, these piles of cut-to-size pieces get moved to my indoor range, kept in two separate piles on the table with the traps, for use as needed. The whole process is repeated as necessary: easy peezy, and as inexpensive as possible. ;-)
Anyway, it keeps the mulch inside. ;-)