Yes, you are reading this correctly, 2 rifles in one combo package 5.56 NATO/223 REM and 300 Blackout (300 AAC) BOTH uppers included! 

The Diamondback DB15 offers high performance and precision in a durable, lightweight, and reliable AR15 rifle platform.  It comes with 5.56 NATO and .300 Blackout uppers with a 16 inch barrels.  Features include an adjustable stock, an optics ready flat-top, and a 30 round magazine.  Diamondback Firearms DB15 rifle uses a gas-impingement system and high quality CNC machined components.  Features a 4140 chrome moly barrel, A3 Flattop upper receiver, carbine length gas system, 12" M-LOK rail, MOE grip, A2 Flash hider muzzle and a Magpul MOE Carbine stock.  Made in the USA.  This model comes with a compatible upper assembly chambered for 300 Blackout.