The difference between recoil operation (left) and blowback (right).
Recoil operation is an operating mechanism used to implement locked-breech autoloading firearms. Recoil operated firearms use the energy of recoil to cycle the action, as opposed to gas operation or blowback operation using the pressure of the propellant gas.[1]
^Hatcher, Julian S. (1 January 1948). Hatcher's Notebook, A Standard Reference Book for, Shooters, Gunsmiths, Ballistics, Historians, Hunter and Collectors. Martino Fine Books. ISBN9781614272830.