The 8.5 mm Mars is an experimental centerfire pistol cartridge developed in the late 19th century based on necking down the .45 Mars Long

.45 Mars Long

The .45 Mars Long is an experimental centerfire pistol cartridge developed in the late 19th century. The similar .45 Mars Short used the same cupro-nickel jacketed bullet in a case shortened to 0.66 inch. The bullet has two deep cannelures, and the case is crimped into both. The case mouth is...

 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

Mars Automatic Pistol

The Mars Automatic Pistol, also sometimes known as the Webley-Mars, was a semi-automatic pistol developed in 1900 by the Englishman Hugh Gabbet-Fairfax and distributed by the Mars Automatic Pistol Syndicate Ltd. of Birmingham. It was manufactured first by Webley & Scott and later by small gunmakers...

. 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

9mm Mars

The 9 mm 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...

cartridge firing a 156 grain bullet at 1400 feet per second. The Mars cartridges were publicized as the most powerful handgun cartridges through the early 20th century; but less than 100 pistols were made and manufacture ceased in 1907.