The Beretta PX4 .40 cal has a problem with trigger sting according to some. I have a PX4 in 9mm and have never experienced trigger sting.
The following is from Beretta's website:
"Trigger sting or trigger slap is a phenomena that may affect virtually any firearm given the right set of circumstances: fit of the firearm to the shooter's hand; physical characteristics of the shooter's hand; how a particular shooter holds the firearm and how that affects harmonic vibrations; and a phenomena, documented by high speed photography, referred to as a secondary trigger pull; and timing; all enter into the equation.
We have done extensive testing on pistols, for example, including where a particular pistol documented as causing one particular shooter "trigger sting", has been fired under the same controlled circumstances by other shooters. These other shooters did not suffer this phenomena.
A Google search of "trigger slap" and similar terms will bring to light that this is common phenomena that affects, as indicated, virtually any firearm given the right set of circumstances. And there are just as many theories as to how to "cure" the phenomena. "