I tend to do things the hard way. In order to practice for making a couple of sporrans, I decided to try to build a saddle. One of the things that learned about saddles is there is a lot of sewing involved. I never would have attempted it had I not learned a simple yet wonderful technique:

Pre-drilling with a dremel tool.

For sewing two pieces of hard leather together, glue them together, then use a stitch groover to give you your line (and it recesses the stitching just a bit), and then use the overstitch wheel to mark the hole spacing (5 stitches to the inch works good). Next, using the dremel tool with a 1/16th inch drill bit, and just drill away. The recess from the stitch groover and the dimple from the overstitch wheel help to guide the drill bit into place, and after a bit of practice, you'll find it is much easier than any other method.

For sewing a piece of hard leather to a flexible one (sporran front to gusset), I go through all the steps above with just the hard piece, and then once those holes are punched, I use an awl to push through the flexible piece to line up with the pre-drilled holes. I'll go about 6 or 7 holes, then sew up to them. Work from the center (bottom) around to both sides because there is a bit of creep going around the curves.

I use a two needle technique, with a needle on each end of the thread, stitching through each hole from both sides, which allows you to keep everything nice and tight. The dremel and 1/16th inch bit give enough room in the holes for easy sewing, and just enough (i need to use pliers) to get the needles through when I backstitch a few holes at the end.

For the gussets, I tried using pig skin, which I had laying around as lining from a holster project I did. Thin and flexible, it took dye well, and really worked well going around the curves. Here are a few pictures.