FN FAL Shortened
The FN FAL wiht a shortened barrel doesn't make an obvious appearance in the new season. Eagle eyed viewers of Strike Back would have spotted one of Martinez's team and several Columbian Cartel guards in the early episodes using the rifle.
The FN FAL assault rifle is of Belgium origin and has been used by several armies around the world including the British army during the invasion of the Falklands.
The DSA SA58 OSW is a close variant to the shortened FN FAL, which has been used in other films such as Sinners and Saints (2010).
The FN FAL has variations built for different militaries. The standard metric-dimensioned FAL was manufactured in South Africa (where it was known as the R1), Brazil, Israel, Austria and Argentina.