I bought a couple that have a velcro strap to go around the forend that I picked up off ebay for $15 shipped. They work great on my AR's, my Sub2000, and my Hera 1911 kit. I also seem to remember my buddy using one on his XCR so I guess they are fairly universal.
I sold my SL8 before I got the catcher but I'm sure it would have worked.
I've had them for a couple years now and there are no signs of wearing out or breaking so if you could build and ship one for under $20 that could also work on an AR I'd give one a try