Diamondback DB15 5.56 Semi-Auto Rifle for sale. Diamondback Firearms is proud to announce its NEW line of DB15 rifles made entirely in the USA. Our AR15 rifle platform starts with the tried-and-true, U.S. Military-proven gas-impingement system and using only the highest quality components machined in Diamondback’s CNC facility. The DB15 raises the bar when it comes to features and performance when compared to others. From the modified Diamondback aluminum four-rail handguard, to a variety of color, sight, and stock options, the Diamondback DB15 represents value and versatility all at a very affordable price. Compatible with most AR15 accessories the DB15 is a versatile rifle system.