Nice score! Nothing wrong with a 4" medium-heavy framed .357 Magnum revolver.
Don't stress about the lack of a DA option. Practice shooting the DA, including dry-fire if/when you can and it will be fine. I honestly can't remember the last time I shot any of my S&Ws in single action and they've had plenty of rounds through them. With time and proper technique even 100-yard targets aren't safe from a DA shot.
NRA Master, Highpower Rifle, Across-the-Course
NRA Expert, Highpower Rifle, Mid-Range Prone