These hold empty magazines adequately, but loaded mags will not stay in place; even a smaller 8 shot .380 mag would not stay in place.
Mag Mount works good for magazines that have one flat side. If your magazine has a raised section all the way around, like an extended magazine with trim, it does not work well at all. Also the adhesive does not adhere to metal very well. It is not sticky enough. Mine has one end that keeps coming loose even with no load on it.