PMAG Magpul Magazine Holder for Stack-on safe door.
This is for the ubiquitous Stack-On 18 gun safe, Model # GCB-18-C.
I liked the Pmag Magazine holder designed by Mikeyman64 (http://www.thingiverse.com/Mikeyman64/about), but I wanted to use it with my Stack-on gun safe without putting any additional holes in the safe, This mag holder mounts to the door of the safe with a simple friction fit. It seems to stay in place rather well with nothing else. Some strong double-sided tape would probably keep in place pretty permanently if you so desired.
This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/5Q03CSQIr2t
This was based on http://www.thingiverse.com/thing:736141
Update: I discovered that after about 18 months, the PLA I used to print these (Hatchbox) started deteriorating. The layers separated and eventually the magazine holders fell apart. This was after 18 months of holding full magazines, which is a considerable weight. I'm re-printing mine with a different PLA and different settings to try to get a better bond between the layers. I had no luck attempting to use ABS, but I think that would be a better material to use for these in the long-run. PLA is a biodegradable material and that may cause it to degrade over time.