The following lists the seasons of the series Black Mirror:
A Beretta 92FS is seen in "Shut Up and Dance"(S3E4)
Several soldiers use FN SCAR-L rifles fitted with EOTech sights, AN/PEQ-15 laser sights, and FN Mk 13 Mod 0 grenade launchers in "Men Against Fire"(S3E5). Though not visually modified, the rifles appear to be intended as a futuristic design, as the gunshot report includes that of a fictional laser or pulse round.
FN Mk 13 Mod 0
Several Mk 13 Mod 0 grenade launchers appear in "Men Against Fire"(S3E5), mounted on the soldiers' FN SCAR-L rifles. Lennard (Kola Bokinni) is seen using one to fire a futuristic device that provides a holographic layout of the surrounding area. Medina (Sarah Snook) refers to it as "the boomer."
Knight's Armament SR-25
A soldier is briefly seen carrying an FN F2000 in "Men Against Fire"(S3E5).
Colt M4A1 carbines are seen carried by British SWAT officers in "Hated in the Nation"(S3E6).