Those Caldwell picatinny-mounted AR brass-catchers are the best of the breed, IMO. I've tried others, including plastic AR snap-on styles and none work as well, are as easy to mount/dismount, or as simple to empty, as the Caldwell version. I liked it so much on my LMT MWS .308 AR that I mounted a second one on my CADEX Guardian Lite precision .308 bolt-gun. They are sufficiently versatile to work on those two completely different breeds of rifle. If you have picatinny rail in front of or behind a unitized scope mount, or rail between your rings, you should be good to go with the Caldwell picatinny-mounted brass-catcher. It is very flexible in its application to most firearms. They are easily found online for $50 CAD. Don't go the cheap $17 Caldwell route - you will be disappointed. Get the more expensive AR version with the picatinny-mounted base that the brass-catcher slides on and off of to mount/dismount. It is worth the extra $$ IMO. Of course, as always, YMMV...