In "First, the Weather Changed" (S1E01), during the CGI intro, guards protecting the Snowpiercer during its embarkation are equipped with HS Produkt VHS-D2 assault rifles.
After the CGI sequence of the intro ends, the guns used by live-action guards shift to what look like Norinco QBZ-97 assault rifles with tactical flashlight attachments. Given that the show was filmed in British Columbia, it is likely that the rifle is the Type 97 variant sold in the Canadian market.
In "Without Their Maker" (S1E04), Erik Sotto (Matt Murray), bodyguard of the Folger family, is shown to possess an early snub-nosed Smith & Wesson Model 10 and makes extensive use of it on the episode.
In "These Are His Revolutions" (S1E08), an over-excited guard pulls what appears to be a Glock 17 during a suspenseful moment of the episode, but is quickly subdued by other guards before he can use it effectively. The scene happens very fast and thus very few clear shots of the gun can be taken.
In "The Train Demanded Blood" (S1E09), a Manurhin PPK with black grips is handled by several characters throughout the episode. It is first secretly given by Martin Colvin (Stephen Lobo) to the teacher Miss Gillies, wrapped in a handkerchief. She then hides it on a convenient spot for Roche to pick up and use against Nolan Grey (Timothy V. Murphy) later on.