I do not know. I don't own a Smith AR. I check out this forum as I own 4 S&W pistols, and a 5th that takes S&W mags. The info here is quite good, and overall, applies to any AR. I do shoot a lot of Bullseye pistol competitions.

As for the Mission First mags, they are relatively new. Maybe since 2014. They started with a blank drawing board, and looked at the strengths and weaknesses of the current poly mags, and tried to eliminate all their shortcomings. The only thing I can think that would make them perfect is if they added the steel reinforcement to the feed lips like Lancer does. But, I'm sure there is a GOOD reason they didn't.