The XO (Jonathan Banks) of the ice freighter 'Canterbury' has a small collection of classic projectile weapons in his cabin, and amongst these is a Single Action Army which he shoots a display screen with as he gradually goes nuts.
Glock 26 Advanced
The "Star Helix Pistol", which is actually a visually modified Glock 26 Advanced Airsoft pistol (a fictional variant of the Glock 26 with an accessory rail, grip extension and compensated extended barrel originally manufactured by Tokyo Marui) serves as the sidearm of many individuals and law enforcement agencies in the series. This includes: Star Helix Security, Tycho Station Security and CPM Security Corporation. Detective Joe Miller (Thomas Jane) and his colleagues carry them, in addition to CPM Inspector Sematimba (Kevin Hanchard) and Amos Burton (Wes Chatham).
Note: In the context of the show, they are described as a "common gun made from plastic polymers so it can be 3D printed cheaply and reliably. It is designed for reliability and ease of use".
Springfield Armory XD(M)
The "Martian Pistol" serves as the standard sidearm of the Martian Congressional Republic Navy, and appears to be a heavily modified version of the WE X Series IPSC Airsoft Pistol, itself based on the Springfield Armory XD. The pistols are later acquired and used by James Holden (Steven Strait), Amos Burton (Wes Chatham) and Alex Kamal (Cas Anvar) throughout the series.
Note: In the context of the show, the weapons are stated to be "designed to fire both self-propelled rounds and traditional cartridge rounds, the rear of the barrel is vented at the back to eliminate recoil for use in zero-g situations".
Umarex Walther Red Hawk
An undercover member of the United Nations tactical team sent to kill the crew of the Rocinante in "Salvage" is briefly seen drawing a Umarex Walther Red Hawk before being gunned down by Amos Burton (Wes Chatham).
Unknown Pistol
Mercenaries working for Mao-Kwikowski Mercantile carry an unknown handgun as their sidearm.
Revolvers
Chiappa Rhino 50DS
An undercover member of the UN Tactical Team sent to kill the crew of the Rocinante in "Salvage" carries a Chiappa Rhino 50DS as his sidearm. Detective Joe Miller (Thomas Jane) later disarms him of it, and begins carrying it as his own sidearm for the rest of the series.
Submachine Guns
TDI Vector
An undercover member of the UN Tactical Team sent to kill the crew of the Rocinante in "Salvage" carries a TDI Vector with an extended magazine and the stock and fore grips removed.
Rifles
Heckler & Koch SL8-4
The "Star Helix Long Gun", which is actually an Airsoft Umarex SL9 resembling a Heckler & Koch SL8-4 with a G36K length barrel, handguard, and various futuristic modifications serves as the rifle of choice amongst many factions in the series. This includes the United Nations Navy, Tycho Station Security, CPM Security Corporation and Amos Burton (Wes Chatham).
APS UAR
The "Martian Long Gun", which is actually a slightly modified APS UAR Airsoft rifles appear as the standard rifle of the Mars Congressional Republic Navy marines first introduced in "Remember The Cant".