In Accelerator's side of the Three Stories arc, Kikyou Yoshikawa uses a Remington 1866 Derringer to shoot Ao Amai after he successfully cripples Accelerator. It is lost after she and Amai shoot each other at point blank and Yoshikawa passes out.
M1911A1
Beretta 92FS
In the Three Stories arc, Ao Amai uses a Beretta 92FS to defend himself as the virus he downloaded into Last Order and the Misaka network loads. When Accelerator temporarily disables Amai and deletes the virus from Last Order with his powers, Amai shoots Accelerator in the head, who cannot immediately reflect the bullet with Vector Change while busy using his power all at once. A suprressed 92FS is also seen in the GROUP shooting range as one of Accelerator's options for a gun in the Skill-Out arce.
VP70
Accelerator settles for a Heckler & Koch VP70 pistol after joining GROUP during the SKIll-Out arc, to compensate for his now limited use of his Eper powers. He doesn' find its grip comfortable, but considers it somewhat better than his other choices.
Glock 17
Walther P5
Walther PPK/S
Colt 25
CZ75
Shotgun
Unknown shotgun
In the Academy City Invasion arc, Accelerator takes an unidentified semiautomatic shotgun from a stolen Hound Dog van. It features a long barrel, a rail-mounted Aimpoint red dot sight, a magazine tube completely concealed within its handguard, and a telescoping wire stock similar to that of the Mk. 14 Mod 1 EBR. Accelerator replaces his cane with it to serve as a crutch for the rest of the arc. He is seen kiling several Hound Dogs with it, while conserving his now limited Esper powers to fight Amata Kihara with later on. Immediately before final confrontation with Kihara, he smashes the shotgun against the Hound Dog holding an unconcious Last Order, destroying it.
Assault Rifle
FN F2000
The Sisters all seem to possess FN F2000 assault rifles for defense and combat, during and even after the Level 6 Shift experiments.
SIG SG552
The SG 552 is seen used by Anti-Skill officers during the battle with the Golem Ellis in the Hyouka Kazekiri and Academy City Invasion arcs. Combined with its featured use in A Certain Scientific Railgun it can be presumed this is the primary firearm of Anti-Skill.
Tavor CTAR-21
In the Academy City Invasion arc, the Hound Dog mercenaries ordered to secure Last Order and hunt down Accelerator are armed with the IMI Tavor CTAR-21.
Sniper Rifle
Barrett M82A1
An unidentified Misaka clone uses a Barrett M82A1 to combat Accelerator at the start of the Sisters arc. It is nicknamed the "Metal Eater", for its full auto setting. Its rounds are deflected back at the Sister by Accelerator's Esper powers, destroying the weapon and injuring the Sister in the process.
Rocket Launchers
Panzerfaust 3
Amata Kihara is seen using a Panzerfaust 3 during the Academy City Invasion arc. He uses ut to shoot at the Hound Dog van Accelerator and Index are escaping in, only for the two to be saved when Vento of the Front teleports in the path of the rocket. Her magical barrier blocks and absorbs warhead's destructive properties.
Grenade
M67 hand grenade
Used by Anti-Skills during the fight with Sherry's Golem.