(set partly in 1905, written in 1922, published in 1922)
[Herbert West] was clad in dressing-gown and slippers, and had in his hands a revolver and an electric flashlight. From the revolver I knew that he was thinking more of the crazed Italian than of the police. The rattling continued, growing somewhat louder. When we reached the door I cautiously unbolted it and threw it open, and as the moon streamed revealingly down on the form silhouetted there, West did a peculiar thing. Despite the obvious danger of attracting notice and bringing down on our heads the dreaded police investigation – a thing which after all was mercifully averted by the relative isolation of our cottage – my friend suddenly, excitedly, and unnecessarily emptied all six chambers of his revolver into the nocturnal visitor.
The handgun used by physician Dr Herbert West in 1905 was a revolver with six chambers. In addition, West fired all shots in rapid succession, which almost certainly means it was a double-action design. A number of suitable patterns were available at the time, but the larger military weapons are less likely. This suggests something like a Colt Double Action Constabulary Revolver in .32 Long Colt (7.9×23mmR), .38 Long Colt (9.2×26mmR), or .41 Long Colt (9.8×29mmR); a Colt New Police in .32 S&W Long (7.9×23mmR); a S&W Hand Ejector in .32 S&W Long; or a S&W Military & Police in .38 Special (9×29mmR) (Investigator Weapons 1: The 1920s and 1930s, pp. 56-57).
The unnamed narrator insists, twice, that one shot would have been enough to bring West’s opponent down, but we cannot be sure whether he took into account that the visitor was a zombie. According to the Call of Cthulhu, Sixth Edition, rules, even six hits from a revolver of any calibre would not be enough to bring down a zombie (average Hit Points 14, takes only one point of damage from impaling weapons) (Call of Cthulhu, Sixth Edition, p. 211). In fact it is game-mechanically impossible to destroy a zombie with less than 14 shots. Even a critical success cannot change this (Call of Cthulhu, Sixth Edition, p. 140), a rule that should probably be ignored. According to the Call of Cthulhu, Seventh Edition, rules, West might have actually brought the zombie down with a single hit to the head (Hit Points 14) (Call of Cthulhu, Seventh Edition, p. 335), provided he rolled good enough to deal with the penalty die and scored an Impale in order to achieve enough damage (Call of Cthulhu, Seventh Edition, pp. 103-104). The latter is much more likely with a .38- or .41-calibre weapon, but not impossible with a .32-calibre.