I cut my plastic a little larger with a band saw,then heat it in a toaster oven, and have a designated press with hinges and lock. Messing with the bar clamps is a pain and use a jig to lay out the holes, then drill with a drill press.
Both ways work good though. I just use the other way since I already have the tools.
I used to drape form plastic windshields for push body show cars, we would get about 6 people with 4 bar clamps each, pull the plastic out of the oven and clamp away like a Chinese Fire Drill. That didn't always produce the desired results
A good way to bend the edges is to make a jig with a 1" deep gap the width of the finished rivet thickness. Heat the edge up, slide the jig in, then bend to your specs. It gives the holster a more conforming shape to fit your body type.The jig keeps the edge from distorting.
I myself prefer a larger radius.
That reminds me to place another order from knifekits.