DAK or double action Kellerman.
There is actually two distinct trigger pulls in the Dak.
The original is about 6.5 lbs.After that there is a shorter release point that allows the shooter to
pull again at about an 8lb pull.This is accomplished by a second fulcrum point internally allowing a
shorter reset or quicker second shot . Here is a paste from an article in shooting times.
I have a p239 sas dak in .40 sw (daily carry) ..I love this trigger system.
After initial firing, the shooter can control the trigger reset either to an intermediate point with a shorter pull distance and two-pound heavier weight (the trigger bar intersects the hammer arm closer to the pivot point) or fully reset to the original longer and lighter weight position.
Externally, the only visible difference between a SIG DAK mechanism and a conventional SIG DAO mechanism is that the DAK trigger has a slightly slimmer profile and the DAK hammer sits completely within the frame when at rest, while the DAO hammer protrudes slightly. Other attractive features include the fact that the slide must be locked back and the magazine removed to disassemble, and it can be disassembled without having to pull the trigger.