Firearm

A flintlock is a type of gun ignition mechanism that was first introduced in about 1630. It was a revolutionary design that replaced the firearm-ignition technologies at the time, such as the matchlock and wheel-lock.

The flintlock became a symbol of its day, and remained in common use for about 200 years until the introduction of new ignition types, such as the percussion cap system, during the 19th century. It was still found in use even after being out-dated by newer ignition systems in wars, such as in the early days of the American Civil War (especially with Confederate forces). The flintlock is still favored by traditional gun powder ("black powder") shooting enthusiasts, and is kept in production for that reason. The flintlock rifle had spiral grooves cut in the bore that greatly improved accuracy and range, but could take several minutes to reload. The slender flintlock rifle of the colonial American frontier has an iconic place in American history. However, most flintlock firearms were smoothbore and fired either a large lead ball or were used as a shotgun - often called a fowler.

The flintlock was renowned for becoming next to useless in the rain, but was a great improvement over the matchlock which required a lit slow-burning match cord that was impossible to keep lit in the rain. In damp weather, shooters would keep a cover of some sort over the lock to keep it dry until use. Most flintlocks had only one barrel and had to be reloaded from the muzzle after each discharge. Civilians typically used a powderhorn and ball bag to reload after each shot. In military use, soldiers used preload paper cartridges that contained both a measure of gunpowder and a ball (bullet) to speed up reloading. Due to the length of time it took to reload, most stationary gunmen using the weapon would carry several spares (often pistols) on them so they did not have to waste time reloading after each round. However, despite its downfalls, the flintlock was a favorite military weapon.

Musket
A musket was typically a military version of a flintlock. It was a smooth bore weapon into the early 19th century. Like all muzzleloaders, it required a tedious reload, however cartridges (a paper tube prefilled with powder and ball) sped up the process. A trained soldier could fire from 3 to 5 times a minute and carried several dozen cartridges in specially designed containers slung over the shoulder or on a belt about the waist. The flintlock musket was in use from colonial times into the first half of the 19th century. A rifled musket was a later military firearm that had spiral grooves in the barrel. The percussion cap rifled musket was the standard issue military firearm by the mid 19th century.

One Piece
The flintlock is the main gun type seen in the series. They are much more advanced than the traditional flintlocks of real life, in that they do not suffer the same reloading time and limited rounds as found in the real life versions. Most of the flintlock weaponry in One Piece are also semi-automatic, something impossible in real life. Both Yasopp and Lucky Roo have been seen using these type of guns as well as many background characters. The guns, however, still fire small, round, ball-like bullets like those used by the traditional guns until the last couple of centuries. The most open use of a Flintlock comes from Mr. 5 who used a flintlock .44 caliber 6 shot revolver (フリントロック式44口径6連発リボルバー), a new model from the South Blue in combination with his Devil Fruit powers. Krieg and Caesar Clown both wield flintlocks with dual barrels, allowing two rounds per shot.

Other type of guns have been seen, such the machine gun found amongst Franky's built-in weaponry; however, they are rarer than the flintlock. The guns used by the World Nobles are also different in appearance, as the one used by Saint Charloss is golden yet somewhat simplistic looking, though Mjosgard used a simple one. Also, Mr. 7 and Miss Father's Day's Yellow Gun and Gero Gero Gun are flintlocks modified to have designs that suit their dress themes.

Other Types of Guns
In the series, there are other types of guns used, and all of their design seems to be based off of the flintlocks, bearing the appearance and mechanism that fits the older times.

Translation and Dub Issues
4Kids reaction to the presence of the guns is to color them green (or blue in a few cases), remove them, or turn them into something else (hammer-gun, arrows, Super Soakers, or cork gun). However, it should be noted this is a common edit with all guns, not simply flintlocks.