My shotgun is not my main HD weapon, but I prefer to keep it safety off with trigger pulled on an empty chamber. Reason being that since fine motor skills degrade faster than gross under stress it should be easier to rack the slide than find / work the safety. This is only my opinion and how I trained when my shotgun was my primary HD weapon and it is natural for me.
ETA: and I would NEVER recommended birdshot for HD unless that is all you had, in which case anything is better than nothing.