One of the guys at Raven Concealment hit me up a couple of weeks ago and asked me to take a look at a new product they're bringing to market. They sent a box loaded with a new magazine carrier that might be of interest:
It is called the "Copia" after a goddess of plenty. I guess because you can have plenty of bullets. I thought it was named after a voluptuous Brazilian stripper, but I've been assured that no Brazilian strippers were involved in the naming of this device whatsoever.
The screw works a tensioner that allows you to adjust the tension in the mag pouch to fit magazines you want to put into it. Pictured is a double carrier holding a Glock 17 magazine and a Beretta 92 magazine. The Glock mag is, of course, wider and typically a mag holder that will hold a Glock magazine snugly won't hold a Beretta 92 magazine with any level of retention. With these you can adjust the tensioner to the point where it will actually provide enough drag to hold even a 1911 magazine when you turn the holder upside down and give it a shake.
They apparently come in singles and doubles. Singles can be joined together with screws if you wish, but the doubles are joined together with longer rivets as you see in the photo.
I've used the Glock 17 mag, Beretta 92 mag, S&W 5906 mag, H&K P30 mag, M&P 9 mag, a S&W 4506 mag, and a Wilson 9mm 1911 mag in the pouch pictured so far, and all seem to be held securely. It works remarkably well with single stack magazines, but you have to be careful how you insert the mag to ensure it doesn't situate at an angle.
The only magazine I have at the moment that flat won't work with it is the double stack magazine from the M&P .45.