Red Dot mounts; If you look at the second from the top barrel in my collection you will see the full S&W rail. The third barrel has only a section of the rail mounted right in front of the rear sight. IMO the 3rd barrel doesn’t have quite enough rail, so take a hard look at what you what you want and where before you drill.
I have had the Docter all over the barrel looking for the fastest place. For me the center of the barrel is the best and reduces my “Red Dot Waffle”.
Your results may vary.

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