I have seen many "permanent" wound channels larger than bullet diameter.
If the bullet hits bone, a blood filled heart or the liver the "permanent" wound channel will be much larger than bullet diameter.

I once shot a deer, a whitetail doe, with a 264 Winchester Mag. with a 100 gr Sierra Spz. The bullet hit the deer right behind the shoulder. It "blew " the deer in half.
The "wound channel" was bigger than my head.
Looked pretty "permanent" to me.