Made this to fit Tokyo Marui Mk23, KSC M93r, and KJW Kc-02 magazines. You know, large ones that don't like to fit standard mag pouches. Probably won't fit smaller mags like 1911 and KJW Mk1, etc.
Since it is meant to be simple and accessible, instead of elastic shock cord the tension is supplied by rubber bands. It is meant to be mounted on a belt or MOLLE with zip ties. Print it twice and attach them to each other. Lateral tension on the mags can be adjusted with zip ties through the side cutouts. Like I said, accessible.
NOTE: The one in the photos is an earlier version without the side cutouts and round rubber band attachment points (which is why they didn't turn out so well which lead to a redesign).
Print it flat on it's back. As long as your bed adhesion is ok there shouldn't be any problems.