Dirty Bird 11.5" 5.56 M4 Carbine Phosphate/Chrome-Lined AR-15 Barrel w/ F-Marked FSB - D265

The Dirty Bird 11.5″ 5.56 M4 Carbine barrel is the short, fast, handy end of the AR-15 lineup — the length that built every carbine you’ve ever seen slung across a plate carrier. Machined from CrMoV steel with a chrome-lined bore and chamber, it’s made to take heat and abuse. That matters more here than anywhere else in the catalog: short barrels heat soak quickly and burn throats faster, and chrome lining is what keeps a hard-used 11.5″ shooting straight long after a bare bore would be washed out.

The 5.56 NATO chamber eats standard 55gr, duty-grade 62gr, and .223 Rem without drama, and the 1:7 twist keeps heavier projectiles stable even at short-barrel velocities. Carbine-length gas is the correct, proven pairing at this length — it’s what keeps the gun cycling when it’s dirty, cold, or running a can, and it’s the reason this configuration has stayed in service for as long as it has. The M4 profile with phosphate-coated M4 feed ramp extension drops into any standard M4-cut upper.

Up front is a pinned F-marked front sight base, the taller FSB cut for flat-top upper receivers. Run a detachable carry handle or a standard-height rear BUIS and your zero lands where it should — no shimming, no holding low.

It ships with the handguard cap, delta ring assembly, and front sling swivel already installed, so it takes standard carbine-length two-piece drop-in handguards straight out of the box. Bolt it up, headspace it, and you have a genuinely compact rifle that clears doorways, rides in a truck, and still hits like a 5.56.

All NFA/ATF rules apply.

Backed by the Dirty Bird lifetime guarantee.

FEATURES

• 11.5″ barrel length — the classic compact carbine spec
• Chrome-lined bore and chamber for extended barrel life under hard, hot use
• Pinned F-marked front sight base — correct sight height for flat-top uppers
• Ships with handguard cap, delta ring assembly, and sling swivel — ready for standard carbine-length two-piece drop-in handguards
• CrMoV (chrome moly vanadium) steel construction
• Manganese phosphate exterior finish
• 5.56 NATO chamber — safely runs 5.56 NATO and .223 Rem
• 1:7 twist stabilizes 55gr through 77gr projectiles
• Carbine-length gas system — proven reliability at this barrel length
• M4 profile with phosphate-coated M4 feed ramp extension
• 1/2×28 threaded muzzle accepts standard AR-15 muzzle devices and suppressor mounts

IN THE BOX

• 11.5″ 5.56 M4 profile barrel
• Pinned F-marked front sight base and assembly
• Handguard cap
• Delta ring assembly
• Front sling swivel