I modified the original design of user functionaldiyer (on Thingiverse) for his Double Stack Magazine Holster, to allow it to hold different sized magazines. My specific goal was for 1911 magazines.
You will need to do some scaling, for correct sizing. For all of the original parts (inner, middle U, outer), you will need to resize them to 1000%.
For my modified middle L-shaped pieces, you will need to resize the long side of the L to the sizes below;
Tall 105.3926mm
Short 67.31mm
The author remixed this model.
The specific parts I modified, are the U-shaped piece. I turned it into an L-shapped piece. There are both short and tall, and thick and thin middle L pieces to accommodate different magazine sizes.