Dahl pistols are semi-automatic when fired from the hip. They fire 2-round bursts when aiming, much faster rate than hip-fire. This gives Dahl pistols high stability when zoomed in and makes them a good sidearm for close and mid-range combat, but not for fight for your life.
The Repeater can come with a variety of barrels, each one can give the gun different properties:
Dahl barrel (stable) – Fires 4-round bursts without reducing stability and with slightly reduced recoil and damage.
Tediore barrel (standard) – Does nothing additional.
Maliwan barrel (elemental) – Increases elemental effect damage (if the weapon spawns with an element) and accuracy.
Bandit/scav barrel ("heavy") – Increases the weapon damage but reduces accuracy.