I was reading a magazine article a while ago about the 9mm in the Glock .
It's premise was that the lighter bullet had to have a higher velocity to be efective , this created a " snapping " recoil and he fould it uncomfortable for all day shooting .
The heavier ( 147 g ) bullet could be loaded so it was slower and had more of a " push " recoil that was more comfortable for all day shooting but still maintaining the power factor .
I can't remember the magazine , about a year ago . They were all reloads not factory ammo .