The 4546 is the full size DAO, the 4586 is the "commander length". The DAO guns have no decocker, as the hammer falls to a sort of "half cock" after each shot.
The 4576 is a traditional double action (DA first shot), and has a decocker.

There are lots of 3rd gen 45 variations out there. I'm sure Smithnut will chime in when he sees the thread, and enlighten us all.

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Eric