Goryumaru (InuYasha) possesses a cannon-like demonic arm that fires lasers.
Lord Yao (Dragon Ball GT: A Hero's Legacy) demonstrates.
Mercenary Tao (Dragon Ball) disconnects his right hand to reveal an arm cannon, from which he fires his Super Dodon Wave.
Gray Fox (Metal Gear) using his arm cannon.
Ash Williams (Evil Dead) making use of an arm-mounted gatling gun.
Revolver Dragon (Yu-Gi-Oh!) lives up to its name, having gun cannon barrels for each of its arms and head.
Slot Machine (Yu-Gi-Oh!) features a Plasma Laser Cannon on its right arm.
Genesect (Pokémon) is armed with a cannon, which allows it to fire its Techno Blast, a powerful artillery attack dependent on the drive installed.
Baby 5 (One Piece) morphing her arm into a hand cannon, among many other possible weapons.
Kujiranami Hyōgo (Rurouni Kenshin) replaced his missing right hand with an Armstrong Cannon.
Commander Brutus (Sonic the Comic) has a raygun in place of a right hand...
...which he uses on Robotnik.
Vash the Stampede's (Trigun) Angel Arm.
Ultimate Humungousaur's (Ben 10) bio-missile launcher/gatling gun.
The Arm Cannon is Samus Aran's (Metroid) primary weapon.
Cyborg (DC Comics/Teen Titans) using his Sonic Cannon.
The KGBeast (DC Comics) has a machine gun for a left hand.
Jolly Roger (Pirates of the Caribbean) has a pistol-like weapon for a right hand.
Dr. Kochin's (Dragon Ball Z) machine gun arm.
Random (Marvel Comics) creates a gun out of his hand.
After using the power of the Tablet of Order and Chaos, Hammerhead Noir's (Spider-Man: Shattered Dimensions) Vulcan machine gun and a missile launcher fused to his arms.
Zero (Megaman X series) with his Z-buster as his secondary weapon.
Franklin (Hunter x Hunter)
Level 1 Akuma (D.Gray-Man) can create a large amount of guns on their bodies (not exactly their arms, perse).
A Level 4 Akuma (D.Gray-man) turning its arms into Gatling guns that fires deadly Dark Matter blood bullets.
Umibozu (Gintama) replaced both his lost arms with mechanical prosthetic that can change into guns.
Astro's Arm Cannon. (Astro Boy)
The Hidden Gun (Assassin's Creed) was an arm-mounted weapon invented by Altaïr Ibn-La'Ahad.
Badnik Amy (Sonic the Comic) had machine gun-esque crossbows mounted on her wrists.
Adam (Buffy the Vampire Slayer) upgraded himself with a collapsible gatling gun/rocket launcher.
Barrett (Mega Man Legends 3)
Mega Man Volnutt (Mega Man Legends)
Bald (Fullmetal Alchemist) possesses a double-barreled rifle in his automail arm.
Super 17 (Dragon Ball GT) uses his Hell's Storm attack.
Metal Sonic (Sonic the Hedgehog/Archie Comics) has a plasma cannon in place of a left hand.
Ginkotsu (InuYasha) using the cannon built into his shoulder.
Duon's pink side fires powerful blue and purple lasers
Vash's (Trigun) machine-gun arm.
Gear REX (Metal Gear Solid: Peace Walker) has a gun-like protuberance that shoots acid.
Barret Wallace (Compilation of Final Fantasy VII)
Arsenal (Young Justice: Invasion)
Shard (Sonic the Hedgehog)
The T-X (Terminator 3: Rise of the Machines) readies its plasma cannon.
The T-70 (T2 3D: Battle Across Time)
The Metallikats (Swat Kats: The Radical Squadron)
Destructor (Futurama) has a Gatling gun installed in his right arm.
The Guyver (Guyver) using the Mega-Smasher, a powerful particle beam cannon in its chest.
Albert Heinrich/Cyborg 004 (Cyborg 009) possesses fully functional gun barrels in his right hand and rocket launchers in his legs.
Mega Man (Mega Man Classic) using his Mega Buster.
Bass (Mega Man Classic) aims his Bass Buster.
Mecha Bandicoot (Crash Twinsanity) has a rocket launcher for a right hand and a plasma cannon for a nose.
A Steel Clan robot (Gargoyles) aims its arm cannon.
Grobyc (Chrono Cross) with the forbidden arm cannon Strong Arm
Bunnie D'Coolette (Archie's Sonic the Hedgehog) utilizes her arm cannon.
Eis Shenron (Dragon Ball GT) performs his Dragon Ball Blast, in which he converts his left hand into an energy cannon.
A Mii Gunner's (SSB4) arm cannon can fire a variety of projectiles and types of energy.
Halloween (Marchen Awakens Romance) has a Weapon ÄRM called Napalm Death which brings a cannon out of his back. The cannon shoots out concentrated flames and each shot is stronger than the one before.
The Ganzu Ragyuuru spell generates turrets from Rodeaux's (Zatch Bell!) wings
Agent Venom (Ultimate Spider-Man) sprouting twin missile launchers from his shoulders.
Metamorphia (Sonic the Comic) turns her left arm into a raygun to attack Shortfuse.
After she was enhanced Seryu (Akame ga Kill) had guns hidden in her arms and even her mouth.
Tiger Claw (Teenage Mutant Ninja Turtles 2012) brandishing a cybernetic raygun arm.
Mercury Black (RWBY) firing his gun leg.
As the Ultimate Spider-Slayer, Alistaire Smythe (Spider-Man: The Animated Series) possesses organic laser guns mounted on each shoulder.
Shortfuse the Cybernik (Sonic the Comic) firing his wrist-mounted laser gun.
Emperor Calus (Destiny) possesses a Gun Arm that fires off powerful projectiles.
Mechagodzilla (Godzilla) firing the Triple Hyper Maser Cannon in its chest.
Yang Xiao Long (RWBY) possesses a gun built into her cybernetic arm.
Turbo Mecha Sonic (Super Mario Bros. Z) possesses a retractable machine gun in his arm...
...which can convert into a missile launcher.
After losing his left hand, Blade (Marvel Comics) used his S.H.I.E.L.D. connections to replace it with a prosthetic gun.