.50 Handgun (Desert Eagle Mark XIX), is the .357 Magnum variant, noted by its fluted barrel and 9-round capacity. The gun operates in DAO (instead of the correct SA) and the slide locks back automatically when a reload is initiated. The pistol fires continuously if the fire key is held.
In series spin-off prequel Contract J.A.C.K., it is introduced as protagonist John Jack's personal pistol to "solve" the personal issues for whoever hired him. It's also one of the most reliable ways to dispatch any foe in the game quickly, perhaps even on par with the combat shotgun. It has high damage per shot and decent fire rate drop a simple thug with a few shots. Only down side to hold it back would be its reload and limited ammo pool which forces you to be accurate.
The game takes place in the 1960s, which makes the Desert Eagle highly anachronistic: the Mark I variant was not introduced until 1982, and the Mark XIX was not developed until 1995.
Desert Eagle Mark XIX on Wikipedia