Wood doesn't allow a bullet room to expand. Animals have hair that can plug a hollow as well and so can fat/tallow.
Notice how the Dold Dot 230 grain 45 ACP bullet expanded, but not the 158 357 Gold Niether the 145 grain 357 bullet and the 175 grain in the 41 nag didn't penetrate well.
The 175 grain JNC penetrated very well and produced a very impressive wound channel
