The “sniper” Manurhin is very much real but I’ve never heard about disguising it as another gun.

Also the GIGN is not really the equivalent of the SAS, although they are both “elite” units, because they only operate on french soil (they’re a unit of the Gendarmerie which is basically militarized police), whereas the SAS are military, and as such, I believe can only operate outside of the UK.

Basically the GIGN are more like the SWAT. Idk about the British equivalent