I printed this cutie but not before remixing it a bit. was not easy. this model has many tessellations. you can see in the pictures i've added recess for the screws and I replaced the spring with a rubber band (in black behind the trigger) giving me full range of motion. Printed in PLA+, Marble texured for the outer shell and Orange for the inner working parts. Works like a charm. 

For zero friction, I've Added a small pulley behind and inside the trigger and added a groove for the rubber to run inside it.

Still considering replacing the screw lead with one which keeps rotating clockwise whether one pulls or releases the trigger.