Not to be confused with
Dirty Magazines such as Playboy or Hustler.
A Dirty Mag relates to the use of a Bullet Type that considered "Bad" or "Not Ideal" for the situation its being used for.
Typically, this is used to describe a mixture of
Hollow Point and Full Metal Jacket in a gun carried for self defense. Since Full Metal Jacket is NOT a safe self defense round due to its ability to overpenetrate. The magazine is a "Dirty Mag".
The name was derived from Dirty Magazines, how they were Taboo to have, and
a Gun's "Magazine".