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."

A colloquism from the American Frontier days, referring to a handgun with a long barrel, as mentioned in the Marty Robbins song, featured in the video game Fallout: New Vegas. It was the style of the time for many to carry shorter barreled guns, often with the front sight filed down or completely off, to aid in a faster draw. So, anyone carrying a long barreled gun was assumed to be confident enough in their ability to handle the gun they would trade the speed of a shorter barrel for accuracy of a longer one.

A large-caliber handgun (Preferably a revolver), that is mentioned in the song Big Iron.
The specific Big Iron was used by The Arizona Ranger to take down Texas Red.

This also is referred to in the hit game Fallout: New Vegas, when you as Courier Six shoot Mister House with a Big Iron, ending the game.

A creepy high school vice principal who likes to sniff poon and torture band kids

If theres a school shooting happening and pumped up kicks turns to big iron the school shooter is fucked

a firearm, more specifically a pistol.

The hardest any single man can get.
You my friend, have truly peaked once you reach the big iron.