Well, I learned a new trick or two. Maybe they have been posted before, if so I missed it.
You may want to mould your leather sheath to your knife for a better fit, or maybe you made a sheath that was slightly too big (no one here would make that mistake, right?).
This is to be done after the sheath is completed but before you apply finish or waterproofing.
Wet the sheath down inside and out. Not dripping wet, but wet throughout. Insert knife, then put them in a food vacuum packer bag and vacuum it. It'll mold the wet leather right to the knife. Wait a few minutes, open the bag, and remove the knife carefully.
Let it dry completely before putting on a finish. Or you can use a food dehydrator to speed up things.
A couple of things to be careful of...try not to get wrinkles in the vacuum bag, as they may show up on the leather. The bags sometimes have a texture to them, it will show up on the leather. You could put in another smooth bag before in the vacuum sealer bag. When drying in a dehydrator, lay on a folded paper towel in the dehydrator, so you don't get a waffle pattern from the dehydrator tray.
Dan