Medical needle-free injection system and method

A fluid injection system, comprising:

• a housing comprising an inner surface and an outer surface which extend from a proximal trigger end to a distal dispensing end along an injection axis;
• a housing top retainer at said trigger end comprising a lower stop socket, an upper pop-in socket, and a venting slot;
• a syringe adapter connected to the dispensing end of the housing and configured to retain a needle-free syringe such that a plunger of the needle-free syringe is movable within the housing along the injection axis;
• a piston retained within the housing by the syringe adapter and movable along the injection axis between a loaded position near the trigger end and an unloaded position near the dispensing end, the piston comprising a piston head near the dispensing end and a trigger catch near the trigger end of the housing, the piston head being movably positioned to bias the plunger of the needle-free syringe along the injection axis;
• a compression spring associated with the piston, the piston and compression spring sized relative to the housing such that the compression spring is compressible along the injection axis within the housing;
• and
• a trigger mounted within the housing near the trigger end and movable between a non-actuated position and an actuated position by depression of a user trigger means positioned at said trigger end of the housing, the trigger comprising a trigger latch configured to engage the trigger catch when the trigger is in the non-actuated position and the piston is in the loaded position and to release the trigger catch when the trigger is in the actuated position.