Like so many things in the world that are admired, cherished or feared, firearms of various types have acquired nicknames over the years. Some are specific to particular styles of guns based on who designed or made them or how they look, sound or were employed — a good example being the Thompson submachine gun. It's been called everything from a "Tommy Gun" (after the inventor John T. Thompson,) the "Chicago Typewriter /Chicago Piano" (because of its popularity with Gangsters in the 1920s and 30s) and "Trench Broom" or "Trench Sweeper," a more martial name it shares with the Winchester Model 1897 Trench shotgun.
Others are a bit more generic. Sometimes their derivation is obvious like "Gat" shortened from the name "Gatling." Another handgun term from around the same time as "Gat" (probably the 1910s) is "Roscoe." Some opine it was coined by writer Damon Runyon as a prop to be used by some of the gamblers and underworld types who populated his stories. Others feel it has a rather naughtier derivation — but as Sigmund Freud supposedly said, "sometimes a cigar's merely a cigar."
The earliest nicknames I've been able to uncover date back to the 18th century. Small, large-caliber pistols were called "Snappers, "Barkers" or "Bulldogs," the latter term coming down to this day, and along the way achieving trademark status.
AKAs such as "Heater, " Shooting iron," "Smoke Pole" and Persuader" are pretty easy to figure out, as are "Saturday Night Special," "Suicide Special" and "Flyapart ," the latter a trio of terms to describe cheaply-made, inexpensive handguns intended for limited, somewhat specialized usage.
"Long Tom", which has generally come to mean an extended-barreled, large-gauge shotgun (it too was ultimately adopted as an official model designation) goes back to at least the 1820s and originally described a large naval cannon. The appellation has since then also been applied to other artillery pieces.
For some time, it was not uncommon for a hunter to call his trusty rifle "Old Betsy" hearkening back to the name given by David Crockett to a flintlock rifle presented to him by some Tennessee constituents that was built by Pennsylvania maker James Graham. He did not have this rifle with him at the Alamo, but passed it on to his son, John Wesley, when he left for Texas. Interestingly enough an "International" cannon made from bits and pieces of parts donated by various military forces during the Chinese Boxer Rebellion of 1900 was christened "Betsy," supposedly a nickname for the Dowager Empress — though I've often wondered if some U.S. Marine might have come up with a name as a tribute to Davy.
"Horse Pistol" originally meant a large military pistol that was carried in saddle holsters, but the moniker mutated to mean any large-caliber, generally oversized handgun.
These are just a few aliases that I came up with off the top of my head. There are others, such as "Peacemaker," Six-Shooter," that I felt were just too obvious to include, but look, I guess I included them anyway. Can't help myself.
Bet there are a bunch I've forgotten. Anybody else out there have some favorites?