The Brownells Retro A2 rifle length barrel replicates the "Government" profile found on the M16A2. Chambered in 5.56x45, this chrome-lined barrel has a 1-7" twist and is finished in matte black phosphate, with an overall length of 20". The muzzle threads are A 1/2"-28 tpi, and in the back a standard rifle barrel extension is pre-installed. 5.56 NATO chamber (also accepts .223 Rem) Original 1-7" rifling compatible with heavier bullets Chrome-lined bore and chamber Requires a rifle-length gas tube (available separately) M16 barrel extension (no M4 feedramps) Non-F-Marked 0.750 inch front sight base (compatible with carry handle rear sights) Available as a Mfg: Brownells