No. Only shoot the caliber printed on the barrel.
uuhhh... no, you cannot fire a 9mm parabellum through a .40 s&w.9mm converted to inches is .35 now you see that .40 is a little wider.
no. nor can you fit a 40 cal shell into a 9mm chamber...............
9mm = .355 40 cal = .40
.355 vs .40
Each weapon will show a preference for a certain lmaker and/or bullet weight. The only way to know is to shoot all the available ones out there.
"Better" is a very subjective word. It depends on what you want, and different people want different things. The .40 caliber round tends to have slightly lower velocity but more muzzle energy than the 9mm, but it depends on which specific cartridges you are comparing. 9mm ammo is (normally) less expensive than .40, so it's cheaper to shoot if you shoot very often.
No
.40 cal hollow points. That is what they practice with also.
The caliber for one.
15 9mm rounds and 10 40 cal rounds
They will "fit" but they will not fire correctly, and will break when the bolt tries to push two of them at once.
9mm is cheeper cause it's a smaller round.