I have a Rock River AR15. It's a great deer killer (never have hit one that got away, and bagged 2/yr since '02), but I'd like to expand it's useful/sporty-ness, and hit up the RRA website. I'm lusting after their LAR-15 pistol, which is just more damn cool than I know how to drool at. I wouldn't mind buying one of those, but I was wondering if I could just the upper, and would it attach to my existing lower (my AR-15 rifle). Both AR-15, both .223, both Rock River... anyone tried this? It would be so much fun shooting squirrels, or helping my younger son target practice with the much lighter 7" barrel. Well? Thx in advance I'm wanting that 7" A4 with the Quad Rail.