Two Calibers, One Platform – The Diamondback DB15 Combo
If you are looking to train your family with two different calibers without buying two separate rifles, the Diamondback DB1721K001 DB15 Combo 5.56x45mm NATO & 300 Blackout 16″ 30+1, Black, Carbon Rec, 12″ M-LOK Handguard, Magpul Carbine Stock & Grip, Includes 2 Uppers gives you both in one ready-to-shoot package. This DB15 ships with a complete 5.56 upper installed and a second, compatible upper chambered for 300 Blackout, so you can switch between calibers in minutes at the range or in the field.
| Manufacturer | Diamondback Firearms |
|---|---|
| Model | DB15 Combo (DB1721K001) |
| Material | 4140 Chrome Moly Barrel, 7075-T6 Upper & Lower Receivers (per manufacturer specs) |
| Compatibility | 5.56x45mm NATO & 300 Blackout (two uppers included) |
| Finish | Black Hardcoat Anodized |
| Weight | 6.8 lbs (approx., with 5.56 upper installed) |
| Condition | New |
Key Features
- Two Complete Uppers: One 5.56x45mm NATO upper pre-installed, plus a second upper chambered for 300 Blackout. Why it matters: you can train with affordable 5.56 during the week and hunt or suppress with 300 Blackout on the weekend using the same lower, trigger, and stock.
- 12″ M-LOK Handguard: Free-float, lightweight carbon-fiber reinforced design with M-LOK slots on all sides. Why it matters: you can mount lights, grips, or lasers exactly where your family needs them without adding bulk.
- Magpul MOE Carbine Stock & Grip: Drop-in, no-gunsmithing upgrade from the factory. Why it matters: the textured grip and friction-lock stock give your shooters a secure hold, even with sweaty hands on a hot range day.
- Gas-Impregnated System & A2 Flash Hider: Carbine-length gas system with a standard A2 birdcage. Why it matters: reliable cycling with both calibers and reduced muzzle rise for new shooters learning follow-through.
- 4140 Chrome Moly Barrel (16″): Button-rifled, chrome-lined for corrosion resistance. Why it matters: this barrel holds up to thousands of rounds of plinking and training, so you are not replacing it every season.
Who It’s For
This combo is built for the family who wants one rifle that does double duty. If you are teaching a teenager or spouse to shoot, starting with 5.56 gives them light recoil and cheap ammo. When you are ready to hunt hogs or deer at close range, swap to the 300 Blackout upper for more thump. It is also ideal for the prepper who wants caliber flexibility without buying a second lower – one serial number, one tax stamp (if you suppress the 300 Blackout later).
Pros & Cons
- Pros: Two calibers out of the box, quality Magpul furniture, M-LOK handguard, affordable price point under $950, made in the USA.
- Cons: The carbon-fiber handguard can feel thin compared to aluminum rails – it is light, but you need to be careful not to over-torque accessories. Also, the 300 Blackout upper does not come with a muzzle device optimized for suppression (standard A2 flash hider).
Comparison
| Feature | Diamondback DB15 Combo | Zev Technologies OZ9 | Geissele Super Duty |
|---|---|---|---|
| Caliber Options | Two uppers (5.56 & 300 BLK) | Single caliber (9mm only) | Single caliber (5.56 only) |
| Handguard | 12″ M-LOK carbon fiber | 4″ aluminum rail | 13.5″ M-LOK aluminum |
| Stock | Magpul MOE Carbine | Zev adjustable stock | Geissele Super 42 |
| Price | $945.51 | $1,899 | $1,799 |
| Best For | Family training, caliber switching | Competition, concealed carry | Duty/LE, precision shooting |
FAQ
Can I swap uppers on my own without a gunsmith?
Yes. The DB15 uses a standard push-pin takedown system. Remove the rear and front takedown pins, lift off the 5.56 upper, line up the 300 Blackout upper, and reinstall the pins. No tools needed. Per Diamondback specs, both uppers are headspaced and tested before shipping.
Does the 300 Blackout upper cycle subsonic ammo?
Yes, with the standard carbine gas system, the 300 Blackout upper cycles most 220-grain subsonic loads reliably. If you plan to run a suppressor, you may want to test a few brands first – some very low-pressure subs may short-stroke. A lightweight buffer (like a carbine H0) can help.
Is the carbon fiber handguard strong enough for a bipod?
For a lightweight bipod (e.g., Harris S-BRM), yes. For a heavy competition bipod with clamping force, I would recommend a one-piece aluminum rail. The carbon handguard is designed for weight savings, not heavy-duty benchrest use. That said, for family range days and hunting, it works fine.
What magazines are included?
This combo ships with one 30-round Magpul PMAG in 5.56. The 300 Blackout upper uses the same PMAGs, so you can share magazines between calibers. Note that 300 BLK may not feed reliably from older steel GI mags – stick with Magpul or Lancer for best results.
Trust & Delivery
- ✅ Nationwide delivery to all 50 states (restrictions apply – ships to FFL only)
- ✅ Ships within 1-2 business days from our warehouse
- ✅ 30-day return policy – if it does not fit your needs, send it back
- ✅ Secure checkout with 256-bit SSL encryption
Related categories: AR Rifles | AR Uppers | AR Accessories
Last updated: April 2026
Buy Firearms Online – Reliable & Affordable
This Diamondback DB1721K001 DB15 Combo 5.56x45mm NATO & 300 Blackout 16″ 30+1, Black, Carbon Rec, 12″ M-LOK Handguard, Magpul Carbine Stock & Grip, Includes 2 Uppers is ideal for shooters looking to buy guns online with confidence. Built with precision engineering and tested performance, it’s a top-tier choice whether you're looking for home defense, sport shooting, or a trusted everyday carry.
Why Choose the Diamondback DB1721K001 DB15 Combo 5.56x45mm NATO & 300 Blackout 16″ 30+1, Black, Carbon Rec, 12″ M-LOK Handguard, Magpul Carbine Stock & Grip, Includes 2 Uppers?
- ✅ Quality guaranteed by top firearm manufacturers
- ✅ Ships fast across the USA
- ✅ Legal compliance and background-check ready
Buy Firearms Near Me – Nationwide Delivery
No matter your location, we ship to all 50 states. Looking for where to buy Accessories near you? FRT-15.com brings the best selection to your door, legally and securely.
Shipping & Return Policy
- 📦 Fast shipping within 1–3 business days
- 🔁 30-day return policy for unused, unmodified items
- 💬 Questions? Contact our support team
Related Firearms
Explore more options: handguns, rifles, shotguns, and trigger kits.
Reviews
There are no reviews yet.