There are still some old lowers kicking around in the military, but most aren&#x27;t that old.  When the Army buys M4s from manufacturers, they&#x27;re getting complete new rifles, with new lowers.  We need some actual military people to chime in here, but I believe that most rifles in current use don&#x27;t have parts on them dating back anything close to the 60s, unlike B-52s, every single one of which has a majority of parts (including the entire airframe) dating back to the original manufacture date between 1952 and 1962.