When dealing with a wildcat caliber you have to reform a standard case to fit your own. Doughnuts or a ring of thicker material occurs down in the neck when reforming a case so that some of the material from the original case forms the new neck. Thats because the body of a case have thicker material than the neck.
The doughnut is not limited to wildcat cases. Depending on brass flow and resizing methods it can occur in any cartridge.
The easiest way to handle it is to ensure the driving band (rearmost portion of bullet that is at bore diameter) is at or above the doughnut region. This region is the neck / body junction. If your chamber (and magazine in a field arm) will accommodate this you can ignore the doughnut.
If your bullet encroaches in this area, you need to inside ream the neck all the way past the neck / body junction.
Proper resizing goes a long way to minimize this. Changing brass may help as well. It’s easier to avoid it than it is to correct it.
Over the years I have seen several elk and deer hides left in the woods by hunters and I have to wonder why they do this? I fully understand and agree about getting the hide off the animal as soon as possible to cool the meat, but why not pack out the hide with you and use it? As far as I know there are no state laws that require you to take the hide home, but to me why waste such a beautiful part of the animal? Some might think they have no use for the hide or it costs too much to tan....