So far, they appear to be able to hold a FS Tib magazine upside quite snugly. Essentially the mag is sealed at the bottom with the top half being held together with what seem like to giant and thick rubber bands. These allow the top to flex open and grip the magazine. I've tried testing in the home, jumping up and down with my holder upside down and the metal mag has remained in place to now. I just need to play with them in the field.
So far thumbs up. Also, the mag holder does cover more than 3/4 of the magazine, so less worry about paint getting in all those little crevices. Though I would keep the open/slot side to the rear just in case.
"All that is gold does not glitter, Not all those who wander are lost;" My MCB Feedback