I don't own any S&W rifles, sorry to say.
I do have 1 AR-15 though, it's a Rock River Arms LAR-15LH, Elite Operator. I got a Left Hand model because being right eye dominant when the ejects on the right side it temporarily catches my eye and takes me off my next target. The left side ejects doesn't bother me in the least.
The only thing I don't like about the gun is the weight. Aside from that it's a great gun. Accurate, almost never jams, I mean like once every 10-15 magazines. Just a solid rifle all around.

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