I have two handguns of similar quality. Both of which I have tried and found reliable one is a full size .40 S&W the other a compact 9mm. Both hold 12 rounds and I will either be carrying WWB 147 grain 9mm JHPs or Remington 180 grain 40 S&W JHPs.
Both weapons are DA/SA the 9 is lighter and somewhat more concealable and the 40 is nominally more accurate. Recoil is comparable between the two th e.40 is a steel framed gun that absorbs recoil and the 9 doesn't have any to speak of
I don’t see a huge difference between the two am I missing something obvious?