M4-contour barrel converts a standard .223/5.56 upper receiver to a dedicated .22 LR upper when used in conjunction with a CMMG, Ciener, or other Atchison-style .22 rimfire conversion kit (sold separately) and magazine (CMMG or Black Dog). Solves the accuracy problems sometimes caused by firing rimfire ammo in the .224" bore of the centerfire barrel. Comes with a chamber adapter and pre-installed barrel extension with locator pin. Installs on a mil-spec upper receiver using a standard or free-float barrel nut. Requires removal of the conversion unit’s .223/5.56-to-.22 LR chamber adapter, using caution to avoid “springing” the unit’s rails, and replacement with the barrel’s chamber adapter. Standard ½" x 28 tpi muzzle threads let you install AR-15/M16 muzzle components. Available in 9.2" length.

SPECS: Chrome-moly steel, black oxide finish on barrel, Parkerized adapter, matte black. 9.2" OAL. .750" O.D. at position where gas port is normally located. 1-16" twist rifling. Ѕ" x 28 tpi muzzle threads.