All single triggers follow the following principles. The trigger "blade" moves from under the sear tail of the first barrel to the second barrel during the firing cycle. All selectable triggers, both mechanical and inertia, have a mechanical link to select which barrel goes first. Upon firing, the "blade" shifts to the unselected barrel.

The bug-bear of single triggers is that when the gun rebounds off your shoulder from its rearward recoil, you will make an involuntary pull of the trigger (second pull). The trigger must defeat this second pull. Mechanical triggers have a dud position or use the second pull to move the blade. Inertia triggers use a fly weight to disconnect the trigger such that the second pull does nothing. I have never seen any data that proves one system is more reliable than the other. Once the second pull was understood, both systems quickly became robust.