Those beautiful K31 bolts are incredibly smooth compared to other straight pull rifles.  They’re also much simpler than the competition.  This next paragraph is going to have a lot of words about just how this works but hopefully the animation I whipped up will be clear enough on its own.

Swiss straight pull rifles feature a bolt body with extractor that does not rotate during operation. Instead a collar, with locking lugs, is wrapped around the bolt body.  This is essentially a cylindrical bearing with a helical channel in one side.  The bolt handle has a rail attached, with a lug that is round in the middle and square at the end.  When retracted, the bolt handle’s square lug compresses the striker spring and its round center slides in the helical channel of the collar, turning it to unlock the lugs.  The bolt handle’s lug would then set into a notch in the collar at the base of the helical channel, locking the striker back and therefor cocking the action on open.  On the return stroke the striker would catch the trigger sear and remained compressed as the bolt handle lug, traveling in the helical channel, turned the bolt body to lock in the receiver.  The large ring at the back of the bolt is a part of the striker.  Pulling this back and rotating it 90 degrees into the left slot essentially de-cocks the gun and prevents the firing pin from reaching the cartridge.

More about this particular rifle can be found at Candrsenal.