Anybody that uses the phrase packing heat is suspect in my opinion and learned all they know of shooting and guns from movies.
You know all the famous stories and movies about the SHOWDOWN in the OLD WEST? One bad guy at each end of the main drag of the town, in a quickdraw shootout?
NEVER HAPPENED. It was all made up by Hollywood based on the old ENGLISH 'dueling pistols'.
All of the bad boys of the old west were shot in the back.
I know! What about all the cops “packing heat”!
Exactly, its a mob term.