In the comic book series Preacher, the Saint of Killers had a pair of magical guns that could never miss and whose bullets were always fatal.
Firstly, the Saint’s guns could miss; the Saint was just very accurate, and being indestructible he had plenty of time to aim. You’re misremembering the description, which in fact says that their hammers would never fall on an empty chamber (as witnessed in his first encounter with Root, where he fires 13 shots from two six-guns without reloading).
Secondly, these guns have already been mentioned in a post near the beginning of the thread.
To refresh my own memory about the “Saint of Killers,” I snagged my copy of Preacher: Ancient History. This is the narrative:
*The Angel of Death gave up his sword.
It was melted down in the last fire that burned in Hell, and from its steel the Devil forged a pair of Walker Colt revolvers.
These guns would not misfire, nor would their hammers fall on empty chambers. No shot they fired would miss its mark. No wound they gave would be anything but fatal.*
The twin guns in Trigun didn’t just
destroy cities. They could only be used by Plants and morphed their wielders arms. On top of that, despite the fact that they turned vast areas into rubble, nobody was ever killed by one (even in July :eek: ) except through normal bullets, although this may just be due to unbelievable luck.
And of course there was the Cross Punisher, a gun that I refuse to believe is physically possible and almost never ran out of ammo. 
Hmm…and Yu Yu Hakusho’s main character has a Spirit Gun built into his finger. What I wouldn’t have given for that power when I was a child.