Whitwabit
US Veteran
Of all the various things to fret over about your day in court, like using your handloads for carry ammo, having trigger mods, etc, running a barrel not made for the gun is higher on the list of legitimate concerns than the others, imo.
So they pull a 9mm slug out of the bad guy, they're looking for a 9mm weapon, they see you were using a Shield 40. Sounds crazier to a gun illiterate jury peer than a trigger kit or some such.
Everyone I know (4 people and myself) that has a model of the 40 S&W and also has a 9mm barrel or 9mm conversion barrel use the 9mm barrel for practice but always carry the 40S&W barrel when carrying .. so really don't think your comment has any bearing on how we carry .. or at least the people I know ..