Diamondback DB15 Combo 5.56 & .300 BLK 16 in.
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About this product
The Diamondback DB15 Combo is a packaged AR-15 platform offering consisting of a complete rifle chambered in 5.56 NATO and a separate, complete 16-inch upper receiver chambered in .300 AAC Blackout. It's built for shooters who value configuration flexibility without the hassle of sourcing proprietary parts. The core system delivers multi-caliber capability with a singular lower receiver.
What is the Diamondback DB15 Combo used for?
The Diamondback DB15 Combo is engineered as a dual-purpose carbine system suitable for general-purpose training, recreational shooting, and as a foundational platform for home defense or hunting with appropriate ammunition. The 5.56 NATO configuration is optimal for high-volume, lower-cost target practice and familiarization, while swapping to the pre-built .300 Blackout upper instantly converts the rifle for suppressed or subsonic use. This approach saves approximately 45 minutes of build time compared to assembling a separate upper from parts.
How does the Diamondback DB15 Combo compare to the PSA PA-10 GEN3?
The DB15 Combo provides a direct, multi-caliber solution within the standardized AR-15/Mil-Spec platform, whereas a product like the PSA PA-10 GEN3 operates on the larger, incompatible AR-10 platform chambered in .308 Winchester. The DB15 Combo is more versatile for shooters who want to toggle between 5.56 and .300 BLK using a single lower and magazines, while the PA-10 is better for those seeking the greater power and longer-range capability of a .308 rifle, albeit with less caliber-swapping flexibility and higher per-round ammo costs.
What does it weigh and what are the dimensions?
The 5.56 configured rifle has an unloaded weight of 6.8 pounds and an overall length of 35.5 inches from buttstock to muzzle. The included .300 Blackout upper receiver assembly, ready for pin-on attachment, weighs 3.1 pounds and shares the same 16-inch barrel length and 12-inch M-LOK handguard profile, making transitions seamless. This predictable package easily fits into a standard 36-inch rifle case alongside magazines and basic accessories.
Who is this NOT for?
This package is not for the precision benchrest shooter demanding sub-MOA guarantees from a match-grade barrel, nor is it for the strictly budget-conscious buyer who will only ever shoot 5.56. The included .300 Blackout upper adds value but also cost; if you have zero interest in suppressed or subsonic ammunition, you’re paying for capability you won’t use. Consider a dedicated 5.56 rifle like the Stevens 334 in .308 for a simpler, more precise bolt-action alternative.
What's in the box?
You receive a complete DB15 carbine chambered in 5.56 NATO, a complete 16-inch .300 AAC Blackout upper receiver assembly (barrel, handguard, bolt carrier group), two 30-round Magpul PMAGs, an A2 flash hider (½-28 thread), an armorers wrench, and minimal paperwork. Critical note: The package contains one lower receiver; you are not receiving two complete rifles. The second upper is designed to be pinned to the same lower via the standard front and rear takedown pins in under 30 seconds. Store correctly by separating uppers and lowers using the included case or a secure rack.
Is the Diamondback DB15 Combo worth it at $945.99?
At $945.99, it presents a solid value proposition for the shooter committed to leveraging both 5.56 and .300 Blackout calibers, effectively offering a second complete upper at a subsidized rate. Building a comparable .300 BLK upper from quality components typically runs $400-$550, making this package a logical buy if you planned to own both calibers anyway. However, if your use case is singular, you may find better value in a higher-tier dedicated rifle or a more specialized platform like an over/under shotgun for clay sports, such as the Stevens 555 Sporting.
Specs at a glance
Pros & cons
What works
- Two complete, caliber-specific uppers for the price of one rifle plus a heavily discounted second upper
- Switching from 5.56 to .300 BLK configuration takes under 30 seconds with standard takedown pins
- Includes two proven 30-round Magpul PMAGs, valued at approximately $30 retail
Trade-offs
- No iron sights or optic included—adds a minimum of $100+ to the true cost of a functional rifle
- The 12-inch M-LOK handguard leaves 4 inches of barrel exposed, which can get hot during extended firing strings
- The A2 flash hider is basic; serious shooters will likely replace it with a muzzle brake or suppressor mount, adding $50-$100
Key attributes
| upc | 810035755079 |
| manufacturer | Diamondback Firearms |
| manufacturer part number | DB1721K001 |
| action | Semi-Auto |
| barrel finish | Black Nitride |
| barrel length | 16'' |
| caliber/gauge | .300 AAC Blackout |
| capacity | 30 |
| color | Black |
| length | 7.5'' |
| magazine included | 2 x 30-Round |
| model | DB15 |
| product type | AR |
| safety | Manual Thumb |
| sights | Optic Ready |
| thread pattern | 1/2"-28 tpi |
| units per box | 1 |
Frequently asked questions
- Is the .300 Blackout upper compatible with any AR-15 lower?
- Yes, the included .300 Blackout upper is built to standard Mil-Spec dimensions and will function with any AR-15 pattern lower receiver that is in-spec. The lower must be configured for a carbine-length buffer system, which this combo's lower already is. No special modifications are required for the swap.
- Does it ship with iron sights or an optic?
- No, neither the 5.56 rifle nor the .300 Blackout upper ship with any form of iron sights or an optic installed. The A3 flat-top upper has a continuous Picatinny rail for mounting your preferred sighting system. Budget for this essential component; a basic set of flip-up sights from Magpul or a red dot will cost a minimum of $100.
- Can I shoot .300 Blackout supersonic and subsonic ammunition?
- Yes, the carbine-length gas system and 1:8 twist rate barrel on the .300 Blackout upper are designed to cycle both supersonic hunting rounds and heavier subsonic loads, especially when paired with a suppressor. For optimal reliability with a wide range of ammunition, ensure you use a standard carbine buffer weight; this rifle ships with one installed.
- How long does shipping take for an online firearm purchase?
- Processing and shipment typically take 2-3 business days after order verification. However, the firearm must be shipped to a Federal Firearms License (FFL) holder of your choice for the mandatory background check and transfer. Total time to pickup depends entirely on your selected FFL's processing speed and local NICS check times, which can add 1-7 additional days.
- Does this work with a standard AR-15 cleaning kit?
- Absolutely. Both the 5.56 NATO and .300 AAC Blackout barrels use common .30 caliber cleaning rods, brushes, and patches. The gas system is carbine-length, so any standard AR-15 cleaning kit from brands like Otis or Real Avid will have the correct tools. Remember to clean the chamber specifically after switching calibers to prevent carbon ring buildup.