[spangy]

This pin can be a royal pain to get back in once removed. I have never seen this pin simply fall out so I have to believe you disassembled it for cleaning ?? Generally one only removes this pin for repairs.

The best way is to relieve the recoil lever of mainspring tension by inserting a suitably sized pin punch in the hole at the bottom of the mainspring guide and pulling up. Once the spring is up the recoil lever can be disengaged from the mainspring. Now aligning the recoil lever pivot hole with the rest of the frame should be easy ... insert the pin. Now re-engage the recoil lever with the mainspring by again pulling up and gently mating the recoil lever to the Mainspring Guide hook.

Have fun but take a break if you're getting frustrated ya ??