It locks up solid as a rock. It does auto-index on the rail just like Bobro says. The “foot” is pressed EVENLY against the 1913 slot ahead of it.
My ONLY concern is the SLIGHT amount of wear (polishing off of the dye/outer layer of anodizing?) that I have noticed on the auto-indexing “bump” and on my upper the “edge” of the rail where it interfaces is shiny, and the anodizing below is darker/more polished, as can barely be seen on the photo.
Normal? Self-limiting? Progressive? What?
It does “roll onto” the upper a lot easier now than it did 30-40 cycles ago and that is a bit concerning.