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.
Design and evolution
During the late 20th century Cybermen invasion, they used standard silver guns, about eighteen 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.
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)