Gun Frontier is a thirteen episode anime series based on the manga by Leiji Matsumoto. It is the fifth animated adaptation of the Harlock franchise and is by far its most unusual entry, changing the setting and genre from a Space Opera set in the 30th century to an action-comedy set in the American Western Frontier.
The Colt Single Action Army "Artillery" Model, a weapon synonymous with the Old West, is by far the most prolific firearm in the series. Harlock usually carries at least one of these weapons at all times.
Colt 1851 Navy
In addition to a pair of SAAs, Harlock also carries a Colt 1851 Navy (for one episode, at least). Several other 1851 Navys also show up throughout the series.
Baron De Noir F. Tat Endale leaves behind a custom-engraved gold-plated Victor Collete Pepperbox when he kidnaps Shinunora.
Matchlock Hinawajyu Musket
The samurai that Tochiro and Harlock encounter in episode 10 all carry traditional Japanese matchlock musket pistols (also known as a "Hinawajyu" or Tanegashima).
The most commonly seen long gun in the show is the Winchester Model 1873 lever-action rifle.
Springfield 1861
The Springfield 1861 rifle makes occasional appearances throughout the series.
Trapdoor Springfield Rifle
Dr. Surusky in episode 5 has a Trapdoor Springfield Rifle with a bayonet affixed to the end, which Tochiro refers to as a "converted Springfield 1861 Infantry Rifle".
Other
Gatling Gun
Shitalnen uses an early-style Gatling Gun attached to an auto-carriage during the final episodes. The weapon is described as being powered by the auto-carriage's engine (as opposed to being hand-cranked) and Shinunora speculates that it is "belt fed", despite the weapon's obvious box magazine.
Railcar Howitzer
In the series's finale, Shitalnen reveals his newly-constructed Howitzer cannon which is hard-mounted to a railcar.