Douglas Harper's Etymology Dictionary
Wikipedia
The pepper-box revolver or simply pepperbox (also "pepper-pot", from its resemblance to the household pepper grinder) is a multiple-barrel repeating firearm that has three or more barrels grouped around a central axis. It mostly appears in the form of a multi-shot handheld firearm. Pepperboxes exist in all ammunition systems: matchlock, wheellock, flintlock, percussion, pinfire, rimfire and centerfire.
The pepperbox should not be confused with a volley gun (like the seven-barrel long gun made by Nock), a firearm that fires multiple projectiles simultaneously by use of multiple barrels. The difference is that a volleygun fires all the barrels simultaneously while the pepperbox is a repeater. The pepperbox should also not be confused with or as a development of the Gatling gun, which fires rapidly by the use of rotating multiple barrels.
Usage examples of "pepper-box".
Then three or four western bad men aspired to clean out the town, were riddled like pepper-boxes for their pains, and public interest turned to other idols.