Hello. I'm new to guns and this is partly I'm asking. I know the difference between a double action only (DOA like my Glock) and single action only (SAO like a 1911), but what's this I see on the SIG website for SAS and DAK? I know they have single action versions because I've seen them, but I'd like some elaboration if that's alright. I've been looking at the p239.