Big Iron: A firearm, specifically a revolver. Due to the thick
metal used in creating old-style revolvers such as the Colt Peacemaker or the newer Ruger Blackhawk/Redhawk, and partially due to the weight of the
weapon, they earned the nickname "Big Iron." This phrase became largely
popular after Marty Robbins' widly successful gunfighting ballad called "Big Iron."
"No lone dared to ask his business no
one dared to make the slip, the
stranger there amoung them had a big iron on his
hip"