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Steve - FWIW, I've made several different holsters, for various shootin' irons - and have yet to buy a pattern.
What I do is unseam a large brown paper grocery store shopping bag & lay it flat.
I draw a straight line down it's center w/a ruler.
Place the gun with it's sights (sic) on that line, but in the middle of the paper (To allow space for the belt loop).
Roll the gun to one side and draw an outline of the gun about 3/4" outside the actual size of the gun.
Depending upon whether a RH or LH holster's wanted, draw an extension on the outline, extending in the opposite direction of the gun's barrel for the belt loop.
Fold the paper in half, drawn lines outside, and cut the paper along your drawn lines.
Place the gun in your new paper holster to make any adjustments in the shape, length/angle of the belt loop, etc ( a new template/paper holster may need to drawn if the 1st one was too far "off").
Transfer the paper holster (template) to the leather, and cut out the leather.
For others interested in holster-making:
Now's the time to do any decorations to the leather, if wanted, before folding/sewing the belt loop, and finally the holster edges.
I place the gun inside some plastic wrap, dip the holster in a pail of warn water for a bit, then holster the gun.
I then rub the leather into a form-fit, using the end of an old (or not
) toothbrush handle, and set if somewhere to dry overnite with the gun inside.
After the leather's dry, I trim the edges and buff them hard (aka: burnish) with some eggwhite & a fast-moving toothbrush handle (again).
Please post a pic of your results, Steve - I (for one) would like to see your labor of love.
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