Cyber-gun refer to weapons utilized by Cybermen of our universe. On other occasions, rather than carrying weapons, they had incorporated them into their bodies. The Cybus Cybermen also sometimes carry Cyber Guns but they are modified to disrupte Dalek shields.
Design and evolution
During the late 20th century Cybermen invasion, they used standard silver guns, about three feet long, designed for two hands. The guns produced a "negative effect" not unlike that made by many versions of the Daleks' gunsticks. (DW: The Invasion)
In 1985, the Cybermen in the London sewers (as well as other Cybermen on the planet Telos) used a somewhat different, smaller, weapon, easier to use with one hand which produced a green halo-shaped discharge. It could easily kill a Cyberman. (DW: Attack of the Cybermen)
The Cybermen landing force that invaded Snow Cap base in 1986 had very different weapons, resembling large, cumbersome sun lamps held at their mid-sections. (DW: The Tenth Planet)
During the 1988 invasion, they used a new kind of smaller, lighter gun. (DW: The Invasion)
The Cybermen seen in 2526 (DW: Earthshock) and transported to the Death Zone on Gallifrey (DW: The Five Doctors) again used the guns used by the Cybermen in 1985.
Doomsday
When the Doctor reveals his Screwdriver dosent kill he says its very good at opening Doors, then Cybermen enter and open fire on the Daleks using the modified energy rifles, temporarily disrupting the Daleks' shields and weapons, giving the Doctor and the humans time to escape. However, the Daleks quickly regain control of their weapons. The Cybermen are still no match for the Daleks and are all swiftly exterminated. As the Doctor and the humans rush out of the chamber, Mickey is knocked into the Ark by a damaged Cyberman and his hand presses against its surface. The Ark is primed, steam gushing from the bottom vents, but Dalek "Sec" says that it needs a space of thirty square miles to activate. The Daleks begin to escort it out of the chamber. Then they are met with another force of Cybermen.
The Pandorica Opens
Just after the Rory has killed the Damaged Cybermen which was trying to get through the huge doors to kill Amy, The Doctor reveals he needs all the weapons they can get and picks up Cyber Weapons and is confused why the Cybermen would lock up one of their own under Stonehenge. Later when the Doctor is about to be placed in the Pandorica by the Allieance the Cyber-Leader arrives with two Cybermen which on of them is carrying a Cyber Gun
Other information
On the Moon's surface in 2070, the Cybermen did not use hand-held anti-personal weapons, but did employ a cannon-sized X-ray laser. (DW: The Moonbase)