S&J Hardware has some of Advance Armament Corporations .300 Blackout 9″ Uppers.

Complete 300 AAC BLACKOUT Upper Receiver Assembly
– 9″ Nitrided 1:7: Twist Barrel, threaded 5/8-24
– AAC 51T BLACKOUT™ Flash Hider
– “Full Auto” BCG
– KAC URX Rail
– Ready to drop onto your AR15/M16/M4 lower! Works with an AR lower with “Mil-Spec” push pin locations.

IMPORTANT NOTES:
-The 9″ and 12.5″ AAC 300BLK Uppers are designed for use with a carbine receiver extension, standard GI Buffer Spring, and an H2 Buffer.

$1499.99