Here are a couple more new photos from this weekend's photo shoot.
The Firemaster helmet and respirator
I replaced the side seams with overlapping seams, and for the center seam I chose a butt seam (since an overlapping seam has to favor one side or the other, and won't be symmetrical).
There are three different types of handsewn seams that I use in my leatherwork: Overlap, butt and plain. Below are the three types illustrated.
The plain seam can add structural strength and really emphasize the seam line, as can be seen on my firemaster's helmet. It is the historically traditional seam for firefighter's helmets, but it requires more effort to shape. On my steampunk gas mask you can see examples of the butt seam and the overlap seam.