Diamondback Firearms offers high-quality firearms that are vetted by the everyday shooter, battle-tested operators, and entrusted police officers at a price point that meets the American blue-collar workers budget. Diamondback firearms start with the tried-and-true, U.S. Military-proven gas-impingement system and use only the highest quality components machined in Diamondback's CNC facility. This DB15 comes with 2 separate upper receiver groups for added versatility. One upper has a 7" barrel and is chambered in 5.56x45mm Nato and the other has a 10" barrel and is chambered in 300 Blackout.