AFAIK 9mm is standard military issue, I have a 9mm auto and a 12GA for emergency use.
9mm and .38 are not interchangeable but almost the same caliber.
I read a bunch before buying my 9mm and you could fill a library with the 9mm Vs .45 debate... and squeeze 10mm & .40 in there just to throw gasoline on the fire... oh and the auto Vs wheel gun debate also.
I ended up going for what
MOST military and police carry seeing as they are professionals at using firearms
(I SAID MOST NOT ALL). And just about everything I read agreed that a 9mm hydro shock will really ruin your day.
I do want to get a 6" .357 mag wheel gun because it is about the most versatile and reliable gun you can have IMHO. You can load it with little girly .38 ammo and let your grandma shoot it or load it with fire breathing .357 magnum rounds all in the same day.
Hey are 15 round clips legal again?