The cycling of the bolt in a Mark II pistol is due to both gas and recoil forces being exerted on the pistol.
It is a blowback design as are most semiautomatic rimfire pistols. This just means that the bolt isn't locked and held into place by a set of locking lugs (like a M-1911). Since the Mark II doesn't have a gas piston it isn't technically a gas operated weapon. Also, since the barrel is fixed and cannot move, it isn't strictly recoil operated one either. However, the forces of recoil play a part in cycling the bolt of the Mark II, since this recoil force is actually created by the backward pressure generated from the expanding cartridge gasses forcing the projectile forward down the barrel. So, these two forces act hand-in-hand to overcome the recoil spring tension and operate the Mark II bolt, thereby ejecting the empty cartridge casing.
To be a strictly gas operated action, it would need a certain amount of escaping gas to be syphoned off and sent rearward through a tube or vent to operate a gas piston, which in-turn cycles the bolt mechanically (like an M-14). Another form of gas operated action doesn't use a piston but the bolt has the piston feature built-in to it and is directly cycled by the vented hot gasses(like an M-16).
To be a stricly recoil operated pistol, the barrel would have to move and break free of a set of locking lugs, which holds the breech closed and the empty cartridge in place until after the projectile has cleared the barrel muzzle (again, like the M-1911).
Here's some useful definitions at the end of this post, to help validate the information I've provided.
Hope this helps,
R,
Bullseye
RECOIL OPERATION: Method of operating an automatic of semi-automatic firearm by making use of the force of recoil due to firing a bullet from the barrel. The barrel recoils under this force, and this rearward movement can be used to cycle the action, ejecting the spent cartridge and reloading the firearm.
RECOIL: The rearward motion or "kick" of a gun upon firing. Recoil in shooting, is the practical effect of Newton's Third Law of Motion: for every action there is and opposite and equal reaction. Recoil is typically explained in 3 separate terms: Generated Recoil; Physical Recoil; and Anticipated Recoil. For more information on recoil see the information block below.
GENERATED RECOIL: The amount of force exerted on the firearms action, stock or grip. The factors affecting this force are the charge or amount and type of powder in the cartridge and the weight of the projectile. The internal pressure is created by the rapidly expanding gasses that are created when the solid propellant or gun powder ignites and turns into a gas. The only way to modify the amount of force is to reduce the charge or the bullet weight. Generated recoil is a constant if all variable are left unchanged.
BLOWBACK: A type of semiautomatic or fully automatic gun design in which there is no mechanical locking of the bolt. Instead, the breech is held closed only by the weight and inertia of the bolt, with some slight assistance from the recoil spring, until the bullet leaves the muzzle. Classic examples of the blowback semiautomatic pistol designs are found in the Browning series of pocket-sized pistols in .25, .32 and .380 calibers as well as the famous Walther PP and PPK series of handguns. Nearly all successful submachine guns, including the popular Uzi and Ingram or MAC 10's as well as the HK MP5 family, use the blowback action. 2. A gun malfunction in which the powder gases escape rearward and into the action.
GAS OPERATION: A method of operating an automatic or semi-automatic firearm by diverting some of the propelling gas behind the bullet into a cylinder where it drives a piston. This piston is connected to the firearm's bolt and, under gas pressure, extracts the empty case and loads a fresh round. Alternatively, the gas can be channeled so as to strike the bolt or bolt carrier directly and thus move it.
GAS OPERATED: A type of firearm design commonly found on semi-automatic rifles, where propellant gas is used in a manor that cycles the action. The most common type of gas operated firearms are the AR-15 / M-16 family of rifles.
RECOIL OPERATION: Method of operating an automatic of semi-automatic firearm by making use of the force of recoil due to firing a bullet from the barrel. The barrel recoils under this force, and this rearward movement can be used to cycle the action, ejecting the spent cartridge and reloading the firearm.
With special thanks to the Gunnery Network for this reference information.