When I made mine I just laid the pistol on a piece of paper and drew a rather generous outline of the profile on the paper.
First draw a reference line using the top flat as a "straightedge". Then, starting at the muzzle, draw around the profile of the pistol, continueing your line under the forend and triggerguard and as far back along the grip as you wish, ending at the breech end of your reference line. Be sure to allow sufficient area for stitching. Next, fold your paper in half along your reference line. Then, cut the folded paper along the profile line you drew. This will give you a rough pattern. You can wrap this pattern around your pistol and see how if fits, the take note of places where any modifications need to be made. The area where the pattern wraps around the barrel is one such spot requiring extra room.
Play with paper patterns until you come up with a design you like, then trace it onto cereal-box cardboard and see how it "fits". If it is to your liking, trace the profile of the cardboard pattern onto the back of your leather. This will become the inside of your holster. Then it is pretty much a matter of just stitching the thing together.
Sorry if the above seems confusing. I just can't express the concept in words very well. It is much easier to do it than it is for me to write about it. Just remember to allow for lots of extrs "trimmin'" area on your leather, since it is much easier to cut it off than it is to add it back on. I haven't yet come up with a satisfactory way of cutting something longer after I've cut it too short. If you or somebody else does, please let this poor boy know!
Good luck!
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