It's a single-action striker fire pistol, so when you rack the slide and return it to battery, the striker is cocked... pull the trigger and it goes bang. A double action like you're referring to cocks the hammer or striker during the first part of the trigger pull then releases it to fire at the back part. That's in simplest terms of course... I'm no gun expert that's for sure. A Shield with no safety is ready to rock when you chamber a round. So as Joe likes to say, you gotta keep your booger hook off the bang switch until you mean business.so what's the no thumb safety? Is it like the hammer is down so when I pull the trigger for the first round the hammer gets cocked and the rest of the pull the gun goes off? I shot a pistol that was like this, the first round was crazy deceiving until I realized what was going on.