[BushpotChef]

As others have said you can use clay but you said you've already got some and aren't really a fan. I buy clay in 500g blocks from the dollar store and roll my own 1/2"-3/4" clays for bird hunting. They hit like a train compared to regular clays or even 5/8 marbles & I actually mixed in some birdshot with a batch a while back & those were devastating.

Best of luck finding something that works!