I've made western side seams from buffalo and deer, suggest Buff. Do center seams from it also. Elk stretches to easily when wet and will probably increase 2 sizes. You can use deer but it wears easily and is great for indoor events (kindof slipper)s. The natives used leather for items the leathers properties suited. Neck and back's thick leather and sturdier properties for those required needs. Clothing needed more supple and flexible needs. Whatever bags or pouches were used for dictated what leather properties were needed. My hard wear and period and historical portrayals dictated the Ft Ligonier Boot. My reenacting group was lucky enough to be given a tour of the Ft Ligonier Historical Society archieve storage and were able to photo and obtain copies of documentation on the making and construction of those artifacts. If anyone wants copies, PM me and I'll tell you what I need to send you copies. It isn't money. Instructions and time is hard, but time consuming part. Making them and then wearing them is the rewarding part.
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View attachment 24211 Summer Ft Ligonier boots, check out the moose neck back soles thickness property. I purchased the sole rectangles as large Moose neck sole rectangles from Lietzau in Minnesota. Way back in the late 1980's
View attachment 24212 Ft Ligs Summer on left, winters on right
View attachment 24210winter pak soles on Ft Ligonier winter boot
View attachment 24209 Winter boot profile (note laced on collar NOT sewn on) This is PC on these. Buffalo neck back soles, not moose.