It is not uncommon for slower, unexpanded bullets to penetrate deeper. This happens because it takes energy to change the bullet. If the bullet doesn't expand as much, the saved energy, carries the bullet further.
The energy for the expansion comes from the powder. The force for the expansion, from the tissue of the animal. Less expansion requires less force, thus less tissue damage.
Your testing indicates the non magnum bullet would be better for hunting deer at 100 yard. The magnum bullet will work, but won't be as destructive, as the non magnum out there.
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