Here's a pic of a west coast/accura .45 200 SWC cut in half, then one side the lead melted out. The plating measured .004-.005 thick. It's also quite tuff or strong, it could take a heavy crimp without "cracking".
Thirties, that don't look like too much crimp to me. Any more than that would result in a buckled case. You need that much to prevent the bullet from working out under recoil and tying up the cylinder.