It has been sometime since I have looked inside on mine, but I seem to recall it being a back action. The thing I remember distinctly about it is the sear. The sear is a vertical bar pivoted close to it's middle. The sear catch is located on it's upper end & engages the hammer on it's outer periphery as far as possible from the axle. The lower end is pushed Forward by the trigger for release rather than up as on most sears. I believe this design would be quite resistant to a "Jar Off".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra