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The Rosco Bloodline 10.5" .300 Blackout barrel hits the sweet spot for what this caliber was born to do: run quiet and run compact. At 10.5 inches you get a little more velocity and dwell time than the shorter 8.2" option while keeping the whole package short enough to wield in tight spaces. Rosco designed these with input from SOCOM end users and some of the folks who helped create the .300 Blackout cartridge, so the twist rate, gas port sizing, and length were all dialed in on purpose rather than borrowed from a 5.56 blank.
This is Rosco's workhorse line, machined from 4150 chrome moly vanadium steel and finished in salt bath nitride for corrosion resistance and easy cleanup. The heavy profile adds rigidity and heat-sinking mass, which helps keep your point of impact steady during faster strings of fire. It runs a pistol-length gas system with a .750" gas block journal and an 11-degree crown, and it weighs in right around 21.4 ounces.
The 1:7 twist stabilizes the full spread of .300 Blackout projectiles, so you can feed it heavy 220gr subsonic match rounds one range trip and 110gr supersonic hunting loads the next without a hitch. The 5/8×24 muzzle threads are the standard for .300 BLK, so mounting a can or a muzzle device is straightforward. Folks running these behind suppressors regularly report smooth, quiet cycling.
If you've got an MK18-pattern upper sitting in 5.56 and want to convert it over, this barrel drops right in. The 10.5" length also leaves room for a slightly longer handguard if you like running lasers or lights like a PEQ-15 or D-BAL out on the rail. Rosco builds every Bloodline barrel from scratch at their Rhode Island facility, and their reputation as an OEM shop for other well-known brands speaks to the consistency you're getting here.
This barrel is set up with a pistol-length gas system, which is what makes it cycle reliably at the 10.5" length. It uses a standard .750" gas block journal, so you'll want a .750" gas block and a pistol-length gas tube to complete the setup. That combination is common and easy to source.
Yes. The 1:7 twist rate is designed to stabilize the full range of .300 Blackout bullet weights, from lightweight supersonic loads around 110gr up to heavy 220gr subsonic match rounds. Builders regularly report clean cycling across that whole spread, especially when running suppressed.
It will. Rosco built the 10.5" .300 Blackout Bloodline as a direct replacement for MK18-pattern platforms currently chambered in 5.56 NATO. Keep in mind you'll still want a .300 Blackout bolt and magazines set up for the caliber to complete the conversion.
The muzzle is threaded 5/8×24, which is the standard pitch for .300 Blackout. That means it accepts common .300 BLK suppressors, flash hiders, and muzzle brakes without needing an adapter.
| UPC | 181969500128 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | BL-105-HB-300BLK-7-P |
| Model | |
| Length | 10.50" |
| Barrel Length | 10.5" |
| Caliber/Gauge | .300 AAC Blackout |
| Product Type | Barrel |
| Color | Black |
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