Oh! I definitely thought about that. I decided to put the snap on the inside so that the outside profile remains faithful to the original. Both the snap and belt loop still work when on a belt but it is a little inconvenient to unsnap it (Though maybe that's good so it doesn't accidentally come undone). But I took form over function on this one.
This is an older Safariland Model 1000 large auto shoulder holster Along with the spring metal clamp that holds things in, there is an adjustable strap for security and a snapped belt loop to keep it from flopping around. There's also a metal "guide along the back welt that helps keep the front sight from wearing into the leather (I guess). They are kind of quick pictures, but I think it shows the major parts. Front to back, I measure 3"; center of the keeper strap snap to bottom, I get 6.8"; the back welt is 0.6" thick.
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Since there's nothing too unique (hardware or otherwise) it's pretty easy to make one with the supplies I normally stock in my leather shop (now that I designed the pattern and figured out how to make it). Just a bit time consuming with all the sewing and detailing.