In Episode 1, when the crew from the Canterbury investigate the Scopuli, they take with them at least one long gun:
The SDCC display showed a gun like this, and the signage called it a Star Helix Long Gun. It’s possible the Canterbury rifles and the Star Helix rifles are subtly different, but the screencaps as yet are not sufficient to show this.
These appear to be based on modified airsoft rifles: The Umarex H&K SL9:
A dummy scope and rail cover have been attached, like the MCRN rifles. The barrel and mock silencer have been removed and replaced with the muzzle of the APS UAR, which can be purchased separately.Additionally, a foregrip has been attached under the barrel.