The Diamondback Carbon DB15 Rifle Combo (MPN DB1721K001) gives shooters two rifles in one package: a main upper chambered in 5.56 NATO and a complete additional upper chambered in .300 AAC Blackout, allowing an easy caliber swap. Diamondback Firearms builds both 16-inch barrels with a black hardcoat anodized finish, a 1:8 twist rate on the .300 Blackout upper, and a 1/2-28 threaded muzzle. Both configurations share a carbine-length gas system and a shot-peened, MPI-tested Mil-Spec 8620 bolt carrier, and a 12-inch M-Lok rail keeps accessories close-coupled on each upper. The combo includes a manual thumb safety and ships with two magazines: a Gen3 PMAG 30-round for 5.56 NATO and a 30-round PMAG for .300 Blackout. Among AR-platform rifles in the AR rifles category, this combo favors shooters who want two calibers on one lower receiver.

Key Specifications

• Includes a second complete upper in .300 AAC Blackout alongside the 5.56 NATO main upper.
• Both barrels measure 16 inches with a black hardcoat anodized finish.
• The .300 Blackout upper uses a 1:8-inch twist rate.
• Threaded muzzle at 1/2-28 on both uppers.
• Both uppers run a carbine-length gas system.
• Includes a shot-peened, MPI-tested Mil-Spec 8620 bolt carrier.
• Features a 12-inch M-Lok rail on each upper.
• Uses a manual thumb safety.
• Ships with two 30-round PMAGs, one per caliber.

Frequently Asked Questions

What calibers does this combo cover? 5.56 NATO on the main upper and .300 AAC Blackout on the included spare upper.

How many magazines are included? Two, one 30-round PMAG for each caliber.

What bolt carrier does this rifle use? A shot-peened, MPI-tested Mil-Spec 8620 bolt carrier on both uppers.

Buy the Diamondback Carbon DB15 Rifle Combo

Two calibers on one lower receiver is exactly what this combo delivers. As soon as it is ready to ship, order it from our Lubbock, Texas gun shop for fast, insured shipping to your FFL.