How accurate are you?
Hot glue some generic asprins onto black construction paper......
This time of year we use clay pidgeons for rimfire targets. They disintegrate nicely when hit edge on.
In the summer, crab apples and over ripe vegetables (cucumbers and tomatoes) are free, environmentally friendly reactive targets.
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."