Air canister for airsoft gun

1. A canister of propellant, comprising:

a cylindrical case;

a hollow head threadedly secured to a first end of the case, the head including an intermediate annular groove on an outer surface;

a hollow plug threadedly fastened in the head, the plug including a first O-ring member disposed thereon, a second O-ring member disposed therein, and a third O-ring member disposed thereon;

a cylindrical plunger disposed through the plug into a first end of the head, the plunger including a first receptacle open to a first end, a lateral first opening through the first receptacle, a second receptacle open to a second end and blocked from the first receptacle, a lateral second opening through the second receptacle, and an annular flange adjacent to a second end;

a hollow cylindrical cap threadedly secured to plug, the cap including a bottom opening communicating with the case, and a biasing member biased between a bottom and the flange to push the flange against the plug;

a hollow cylindrical passage member threadedly secured to a second end of the case; and

a check valve threadedly fastened in the passage member, the check valve including an annular recess on an outer surface, an axial passageway, a lateral opening communicating the axial passageway with the annular recess, and a O-ring element disposed in the annular recess to block the lateral opening of the check valve;

wherein the O-ring element is configured to unblock the lateral opening of the check valve in response to pressurized gas passing through the lateral opening of the check valve; and

wherein in response to pushing the first receptacle inward, the biasing member is further compressed to move both the first and second openings between the first O-ring member and the second O-ring member, thereby flowing pressurized gas in the case out of the head via the bottom opening of the cap, the second receptacle, the second opening, a gap between the plunger and the plug, the first opening, and the first receptacle.