Kinetic Destroyer
Kinetic Destroyers are master-crafted Archaeotech Pistols, that are wielded by the Adeptus Custodes' Custodian Venatari. These gun-slinging flying golden eagle bois seem to carry these things around in bulk, which leads credence that these things aren't as rare as one might suspect an archeotech weapon would be, and instead they are weapons made exclusively to the Emprah's finest.
Anyways, Kinetic Destroyers obviously fires a physical round; it's in the fucking name. However, what type of weapon this thing is, is a source of Skub, it doesn't really help that it is an archeotech pistol anyway and we all know how esoteric these things are. At the very least, we know it is a giant revolver, like that of a Stub Revolver. But whether it is a Stubber or an Autogun is up anyone's alley. A third answer however, could state that these pistols are actually a form of Railgun or even a actual Gauss weapon (No, not the Necrons weapons which are anything but a Gauss gun).
On tabletop, the Kinetic Destroyers are the only pistols in Forgeworld Custodes guns. 18" Pistol 2 S6 AP-2 D2 can score an additional hit on unmodified roll of 6. MEQ/Primaris/TEQ killers with enough range to put you out of rapid fire range of most troops.