This batch of test run EMR-MCXs have been made into key rings. They're fully functional, but we're not satisfied with the quality (serrations are not as sharp as we like), we don't want to sell them but also don't want them to go to a landfill, so we elected to make them into key rings. If you do decide to use it on your SIG MCX, it works as designed even with the slightly blunted serrations.
EMR-MCX is a magazine release button designed for SIG MPX.
We used the same proven and successful EMR curved and horizontally serrated surface on the EMR-MCX as well, with the same self centering, and vertical movement mitigation features. We're not fans of flat control surfaces, a simple (but expensive to machine) curve does wonders for the AR15/M16 spec EMR button. Combined with effective horizontal serrations, the design auto centers the user's finger and mitigate vertical movement of the finger. The distinctive curved and serrated surface is helpful in identifying the magazine release button without a visual, in an otherwise flat and featureless receiver surface. The curved surface does even more for EMR-MCX, as SIG MCX's magazine release button is much longer than TDP magazine release buttons.
Machined from 4140 steel and black nitrided, EMR-MCX is proudly designed and made in the USA.