Gun holster design is much the same as many other types of leather case, and can be done using the same basic principles of layout.
These principles design and make holsters that actually fit the gun they are intended for use with. For contrast, the store gives me a bag to hold what I purchased. This bag holds my purchase, but does not fit it. A holster should fit.
Theory and layout
This simple pancake style will quickly get you started making your own patterns to make leather holsters.
This type is sometimes called a “50/50 pancake” due to the front and back being basically the same, placing the stitch seams along the center line of the gun. This type of holster is very basic and a good place to start.
Make your own avenger style leather gun holster pattern using the how to example of a Springfield 1911 with 5-inch barrel.
Alter your pancake style OWB holster pattern for use as a basic IWB holster.
The reason my holster pattern making articles recommended using “half the width of that side plus the leather thickness” to lay out and make holster patterns.