glocks perform two actions when you pull the trigger: cock the striker spring, and release it. that technically classifies it as double action.
...on the other hand, springfield XD's are single action: racking the slide "cocks" the striker spring, while pulling the trigger simply releases it and therefore only performs one action.
Most of these types of guns, Sig P365 included, are generally referred to as double action despite the way the function internally. You pull the trigger and get one shot and a complete cycle which readies the next shot. They do not have an external safety.
My primary home defense weapon is a Beretta Model 96, hammer fired. I store it uncocked with a live round in the chamber and the safety off. On the first round I need a strong trigger pull to cock the hammer and then drip it. Then it cycles, reloads, and cocks itself. After that all I need is a relatively light pull on the trigger to fire the weapon.
Going to the Sig, if you start with a chambered round, does your first pull on the trigger cock the striker and then drop it, or is the weapon already cocked for that first shot, resulting in a much lighter trigger pull? Please pardon my ignorance.