The 1st Gen "Martian Pistol", heavily modified version of the WE X Series IPSC Airsoft Pistol, itself based on the Springfield Armory XD continues to be used by James Holden (Steven Strait), Amos Burton (Wes Chatham) and Alex Kamal (Cas Anvar) after they acquired them in Season 1. It is suggested that by the time of the second season, these pistols are now in the process of being replaced by the MMC.
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".
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) continues to serve as the sidearm of many individuals in the series.
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".
Martian Pistol (2nd Gen)
In "Safe", Martian marines are seen loading up what appear to be a newly upgraded sidearm to those used by the MMC in the first season. They look similar to the sidearms used by the Protogen mercenaries in the first season.
An member of the OPA team sent to breach the spin station in "Safe" carries a TDI Vector.
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 is seen carried by multiple members of the OPA team sent to breach the spin station in "Safe".
APS UAR
The "Martian Long Gun", or variants thereof, which is actually a slightly modified APS UAR Airsoft rifles are seen in the hands of multiple members of the OPA team sent to raid the spin station in "Safe".
Beretta Cx4 Storm
The 2nd Gen "Martian Long Gun", which appears to be a heavily modified version of the Beretta Cx4 Storm is seen on a gear table aboard the MCRN Sirocco in "Safe". It appears to be an updated version of the rifle used by the Martian Marines in the first season.
FN SCAR-L
A heavily modified SCAR plays the part of Amos's trademark auto-shotgun. A magwell cover prevents the type from being identified.
Machine Guns
GE M134 Minigun
The Rocinante, a former MCRN ship, is armed with multiple miniguns resembling the GE M134 Minigun.
Other
Martian Marine Corps Armour
Updated mechanical armour worn by members of the MMC, including Gunnery Sergeant Roberta "Bobbie" W. Draper (Frankie Adams), is equipped with machine guns built into the arms, and what appears to be a small missile launcher in the back.
Triple Barrelled Cannon
A remote controlled cannon with three barrels is seen in "Safe", firing dummy rounds during a training exercise carried out by the MMC.