I bought this upper for a tripod-mounted super safety rig and I just never could get it working with my butterfly trigger. Functions great with a normal stock and trigger. Only a couple hundred rounds through it, it's in great condition. It's the Borebuddy economy 16" upper, with super safety sear trip, tuning kit, dryfire block, pressure plug, etc, etc. All the awesome stuff you need to really tune these things. All in all it was around $800 from Borebuddy, and I'm letting it go for a steep discount to free up money for other projects.
It will also come with a number of high-quality KRISS magazines and a drum.
$400 cash for everything, face to face at the New Braunfels Academy. No trades, except +/- cash for a .38/.357 threaded lever gun, an Atlas Super CAL bipod with ARCA, a Beretta A300 sporting 12ga, or a Yildiz HPS Sporting 12ga.