The Diamondback DB15 Combo is an AR-pattern pistol package chambered in both 5.56x45mm and .300 Blackout, with a 7-inch barrel for the 5.56 upper and a 10-inch barrel for the 300 Blackout upper. It has a polymer grip, M-Lok handguard, and Flat Dark Earth finish. The package ships with 30-round magazines. 
 

Key Specifications 

• Brand: Diamondback 
• Model: DB15 Combo 
• Caliber: 5.56x45mm / .300 Blackout 
• Action: Semi Auto 
• Capacity: 30+1 
• Barrel Length: 7" (5.56) / 10" (.300 Blackout) 
• Color/Finish: Flat Dark Earth / Black Nitride 
   

Detailed Features 

• Two-upper combo: 7-inch 5.56x45mm upper and 10-inch .300 Blackout upper included 
• M-Lok handguard for accessory attachment 
• Polymer grip 
• Flat Dark Earth finish on the receiver; Black Nitride barrel finish 
• 30-round magazine capacity

Owners of the DB15 Combo appreciate the two-upper package concept, calling it a practical way to get two calibers on one lower. The ability to switch between 5.56x45mm and .300 Blackout without buying a second pistol lower is cited as the main draw, especially for range variety.

The M-Lok handguard and polymer grip draw mixed reactions. Most find the ergonomics acceptable for a pistol-format AR, but some owners swap the grip immediately. The Flat Dark Earth finish holds up well in typical use, though a few note the aesthetics are purely utilitarian.

Value is where the DB15 Combo tends to win. For buyers who want the flexibility of two calibers, the combo price undercuts buying separate uppers and lowers. The common gripe is that the trigger is serviceable but not refined, which pushes some owners toward aftermarket replacements early on.