Marston is the affectionate name given to a particular .44 Magnum Taurus Raging Bull currently in possession of Dusk Gleam, who was way too nervous to consider wearing him for the longest time. Despite being inanimate (or is he?), Marston is referred to as a male.
Just look at him! He shoots bullets, pow pow!
Unlike most firearms, Marston has an as-yet-unexplained N-D mechanic that allows him to generate, hold, and fire an indeterminate number of bullets, without the rounds or their casings weighing down the user. This is an infinite magazine, not just an infinite clip. The only drawback is that if, for some reason, one opens the chamber, one will fill the room with all the casings generated since the last time they did it.
Marston does not require cleaning, perhaps as a side-effect to the apparent wanton warping of bullets into and out of his chamber.
Marston has probably killed about 60 billion living things, at least half of whom deserved it.
Before the events of The Une Invasion, Marston was just a regular old revolver. Granted a big one, but still just a Revolver.
And then one time Jake was acting so completely idiotic that Dusk thought a demon had possessed him - especially since his evil self had just been seen mocking everyone and the past week had been full of ghost hauntings - and threatened to shoot him, you know with Marston, which was a bit of a bump for the trust thing but that smoothed out.