The latest EMR features a slightly curved button surface to fit the natural curvature of your finger. The form fitting curve, along with the All Angles dimpled surface, allow for positive indexing during intentional magazine removal. The EMR-HC is closed on the side of the dimples for the magazine catch's shaft, and portrudes 0.08" over the magazine release fence.
The EMR-HC is recommended for 7.62 ARs but will work on 5.56 AR-15s.