I have a Sig m17 and on occasion have had trouble reinstalling slide onto the frame. After reading several posts on the subject I am somewhat confused as some say the front with 2 flat sides are positioned to the left and right of the slide. Others seem to indicate flats facing untoward barrel and to the bottom of the frame.
Can anyone instruct me on what the correct install would be? Please note the rod and spring is full size with spring captured.

I was not aware that any full size P320/M17 recoil spring guides had flats on the rear flange, so I don’t know from personal experience. My 2018 armorer manual, however, does state that the guide rod used in sub-compact models does have flats, and that they should be vertical for installation when the slide is lying on its top. I.e., the flats should be towards the sides of the slide, not the top and bottom.

The large end is round that sits against the barrel. It’s the other end which is a bit smaller that has two flat sides cut into it. Oddly it would seem as long you you install the larger round end against the barrel it shouldn’t matter how the smaller end is oriented. Maybe my issue is being caused by something else. I guess maybe I’m just grasping at straws. Thanks for you in put.