The 8.5mm Mars is an experimental centerfire pistol cartridge developed in the late 19th century based on necking down the .45 Mars Long case. The bullet has two deep cannelures, and the case is crimped into both. The case mouth is chamfered on the outside to fit flush into the forward cannelure. This elaborate bullet seating was necessary to withstand the violent feed mechanism of the Mars Automatic Pistol. The cartridge headspaces on the shoulder adjacent to the neck. The case has a thin rim and deep extractor groove in comparison to most rimless pistol cartridges. There was a very similar 9mm Mars cartridge firing a gr ( g; oz) bullet at ft/s ( m/s). The Mars cartridges were publicized as the most powerful handgun cartridges through the early 20th century; but less than 100 pistols wer