In armed robberies, beating the victims with firearms is usually more common than to shoot or stab them. You usually either Buttstroke someone with a rifle or pistol-whip them with a handgun. This is the quickest melee attack.
Weapon Butt is a melee option available in PAYDAY 2. It is available to players at any reputation.
If a player wishes for more knockdown, use Martial Arts Aced.
As the fastest melee option (in the initial strike, not with subsequent hits), it is viable for cancelling a reload, especially for weapons with lengthy reload times. However, sprinting for a split-second can achieve a similar effect, unless one has Parkour Aced.
The weapon butt is useful for rapidly smashing multiple display cases (or other breakable objects) in a short period of time thanks to its exceptionally rapid followup speed.
If one were to add the Bayonet onto the Nagant, it has a special effect if using the Weapon Butt: Instead of using the weapons "butt," it uses the bayonet, which is essentially a Weapon Butt with better stats.
The Weapon Butt uses what looks to be the stock of an AMR-16 as its inventory icon.
Despite the name, the Weapon Butt's attack animation does not always involve hitting one's enemies with the stock of their gun. In fact, in some cases the point of impact can be anything but the stock, up to and including the muzzle and magazine.
Performing a Weapon Butt attack will always connect even if the equipped weapon doesn't have a stock (anymore). This can best be observed when using a weapon equipped with a mod that removes the entire stock from the model.