I bought this gun for my wife. We took it out to the range for the first time and put the first 50 rounds through it. I went to eject the magazine to reload, and the mainspring housing pin fell out into my hand. I have a few questions about this:

1) Is the pin tapered, and therefore directional for reinstallation?

2) Would there be an issue in putting a smear of thread locker on the frame's pin bore before reinstalling the pin?

3) Has anyone else had this happen?

The pin is not tapered and should NOT need Loctite. The pin should be held in place by part #33, if you look at your owner's manual. Call SIG and have them fix it or send you the part.

Welcome to SIGforum, by the way.

Thanks, Gary! You nailed it. I had installed a lower trigger pull spring set from M*Carbo and left that part secured in the original spring. Easy fix. Salute!