Here's my now complete .450:
20" upper
Spike's
Tactical lower with Rock River LPK and ACE stock
Magpul Flat Dark Earth color Duracoat with MOE grip
Leupold Ultimate Slam scope on a LaRue LT-104 mount
I took it out to the range today; it functions perfectly. Feeds, fires, extracts, all without problem. Recoil is surprisingly mild; it kicks like my Remington 105 CTi II shotgun (in other words, not much at all). It's quite accurate, much more so than the shooter.