Mil-spec is a VERY loosely used term in the AR world! The US department of defense determined what "specs" needed to be done in order to be TRUE Mil-spec.
Dimensions are NOT the only determination for "Mil-spec"
The type of materials used, Process for anodizing it, Certain parts (bolt head, barrel) need "metal particle tested", Barrel & chamber have to be chrome lined. Grade 8 bolts for the gas carrier key & properly sealed and staked! Just to mention a few "specs" needed to be TRUE Mil-spec.
Food for thought.
Dimensions are NOT the only determination for "Mil-spec"
The type of materials used, Process for anodizing it, Certain parts (bolt head, barrel) need "metal particle tested", Barrel & chamber have to be chrome lined. Grade 8 bolts for the gas carrier key & properly sealed and staked! Just to mention a few "specs" needed to be TRUE Mil-spec.
Food for thought.