Meson gun

When Group Marshal Nathan and his subordinate of the Tenth Sontaran Battle Brigade entered the TARDIS control room after being lured there by the Sixth Doctor, the subordinate Sontaran wielded a bladed gun. (HOMEVID: A Fix with Sontarans)

Sontaran ships such as Linx class cruisers and Valt class destroyers were fitted with meson cannons, which were open-ended particle accelerators. (PROSE: Lords of the Storm)

Behind the scenes
In the original version of A Fix with Sontarans, Jimmy Savile identifies the weapon as a BBC meson gun, however this ending was cut from the 2022 edition of A Fix with Sontarans — given ethical reasons over Savile's illegal and predatory behaviour — and it is also not a valid source due to the fourth wall breaking ending. As such, it is never named in the 2022 version.

Information from invalid sources
According to one account, after the Doctor and Tegan congratulated Gareth Jenkins on killing the duo of Sontarans, Jimmy Savile entered the TARDIS and told Gareth that, as the Sontarans wouldn't need the weapon on account of being dead, that he could take the BBC meson gun. (NOTVALID: A Fix with Sontarans)