I have a Colt Model 1911 .45 Caliber pistol that I wanted to put in a holster. I had seen formed holsters and thought I would give one a try. I made the holster a few years ago, so I will step through the process. Please let me know if you have questions.
Step 1: Forming
This is very heavy weight leather, probably about 8 oz (just under a quarter inch thick). I cut two squares that would cover the pistol. When I had the two pieces cut, I soaked them thoroughly with isopropyl alcohol.
(LESSON LEARNED: If I were to do it again, I would use water. The alcohol REALLY dried the leather out, which forced me to put a lot of Neatsfoot oil on it at the end)
When the leather was soaked, I put the gun in a plastic bag, and sandwiched it in between the two pieces. I then put the whole package into a vacuum bag and removed the air. This caused the leather to form right around the pistol. Then I used a deer antler to bring out the detail around the edges. With the bag sealed I taped the bag around a coffee can. This provided the form/curvature so the holster fit on my hip.
When everything was secure, I cut the bag open and this allowed the leather to dry, which allowed the forming to become set.
Step 2: Assembly
When the leather is dry it comes out like a big square with a gun outline in the middle. At this point, glue the two halves together. I use Barge Cement, but E6000 would also work. The important part of this step is to ensure that the two outlines line up perfectly. Use clamps while letting the glue set, or you can vacuum bag it again.
With the holster glued, it is time to layout the shape of the outline. The important part is the layout of the belt loops so the holster is in the proper angle when worn.
When you have the angle correct, freehand the desired outline with a pencil. When you have the outline complete, to include the belt holes, cut it out with a razor blade (or you could use a band saw). I drilled the ends of the belt loops with a 1/4 inch drill bit, and then cut the slots between the two holes.
When the final shape is completed, layout the stitching with a pencil. With a leather stitching groover, follow the lines to create a small channel for the stitching. You can use an overstitching tool to layout the spacing for the stitching, then I used a 1/16 inch drill bit and drilled all the holes.
Step 3: Sewing
I stitched over and under, and then came back through the opposite holes so that there were two passes over each set of holes. You can see the technique in the second photo.
To finish the look and give it more strength I drilled four holes and fitted them Chicago screws (from Tandy).
When it was completely sewn, and screws were installed, I finished the edge with a chamfer tool. To clean up the roughness of the cut, I sanded the edge with a belt sander. This really gave it a finished look.
Step 4: FINISHING
The final step is moisturizing the leather with Neatsfoot oil. This really darkened the leather.
The project was not as difficult as I thought it would be, and it was very satisfying to have completed. Best of luck.