A 9mm pistol is a pistol that fires a bullet which is 9 MMs in diameter.
No
probably If the pistol is designed for 9mm Luger, 9mm Para, or 9x19, yes.
Perhaps the most common 9mm CARTRIDGE is the 9mm Parabellum- commonly called the 9mm Luger. And it IS for an automatic pistol (and carbine and submachinegun). However, there are probably a dozen or more OTHER "9mm" cartridges- many fairly scarce- such as the 9mm Makarov, 9mm Browning Long, 9mm Kurz (the .380) etc. They are different and do not interchange.
The 9mm pistol would have the higher decibel rating.
6 mm
No
Most likely a 9mm with a suppressor
9mm MKV is not the same as 9mm Luger.
The 9mm Parabellum is longer than the .380 ACP (also called the 9mm Short) They do not interchange.
The answer is arguable, as there are a lot of very reliable 9mm pistols out there. One pistol that I have never had problems with, and that has a reputation for having both excellent reliability and accuracy is the SigSauer P226.
It is 9mm pistol