Greetings and Salutations to one and all.
Bitterwheat Pard, I use a process for pattern making that is shown by both Al Stohlman, and John Bianchi. By the way I recomend both Al's Books, and John's vidio.
I use a manilla folder, but you can use a brown paper bag, cut and open. I am going to explain it for the folder, for the paper bag or any large sheet of paper just fold it in half and work from the fold.
Useing the folded edge, place pistol upside down on the fold. For ease of explaination we will position the fold away from you, the bore axis of the pistol will be paralell to the fold and across your front. Line up the folded edge with the rear sight notch and the front sight. Rotate the pistol twards you and lay flat on the folder. Note: The sights will no longer be aligned with the edge. Trace around the pistol, I like to use ink to outline the pistol. Now you can draw your holster pattern over the outline, I like to use pencil to draw the holster pattern.
Depending on the thickness of the leather you will need to make the holster margin a half inch or more away from the pistol's outline. When you have the pattern drawn, but before you cut it out, place the pistol in the folder and pinch it togeather at the holster line and see how it looks. You might even be able to hold it up to the light to check the line.
Now go back and add a quarter inch to the mainseam line. When you cut it out remember that you can cut both pieces when you cut the main seam, but only cut the front sheet when you cut the throat profile. An exception to this would be some of the Slim Jims. The back sheet can be bent down at the belt line and used to form the belt loop, or the backflap for a Mexican Loop. Most likely you will have to graft more paper to the back sheet to make the size.
Most of the time after I cut the pattern out and I put the Pistol into it I find that it is going to be tight around the mainseam. The nice thing is that folders are cheap so you can afford to toss it if it isn't right. An even better thing is that you can tape the scrap pieces back on to the edges redraw and recut.
I hope this has been of some help to you. I am sure that this explaination has been as clear as mud and probably not much help, but it is the best I can do for you. I am sure that some of the other Pards can straighten out the rough spots and make it make sense.
Just my two bits in the kitty.
Regards, Beaumont