...could fairly be considered a combination of these two shots of Travis Bickle (Robert De Niro) from 'Taxi Driver'.
It looks to be the same caliber/barrel-length revolver, there is a 'tunnel/hallway' element, and Gilgun even seems to be doing a hammy De Niro impression.
If Hydell says anything akin to 'You talking to me' in 'Lock Out' it'll be straight homage. The guys would have known that Hydell looked like Bickle post mohawk and would have joked about it. It'll be fun to see what reference to 'Taxi Driver', if any, makes it into 'Lock Out'.