Originally Posted by 40cal

Did you buy your sigma New or Used? Sounds like your trigger bar is not reseting, make sure the bar is seated under the sear block pin, and the spring at the trigger assembly is providing an upward tension on the bar.
If the pistol is used then anything is possible.(backyard gunsmiths)
If the pistol is new then S&W should take care of it. I have not heard of any "bad eggs" lately though.