My "fun" or general-purpose AR. Base gun is a Bushmaster 16" custom Dissipator upper assembly with 4-rail rifle-length free-float tube, on an assembled-by-me lower. Burris E-1 variable power 2-7x scope with multi-distance reticle in a RRA quick-detach mount; back-up iron sights; Magpul stock, pistol grip, and vertical grip; RRA two-stage match trigger; Harris bipod for longer shots off the bench or prone; Lancer L5 transparent magazine so you can see the money/ammo you are about to convert into smoke and noise. Useful for most types of AR shooting or hunting, but specialized for nothing in particular.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)