I've lived out west and hunted elk in Wyoming and No One, including myself would step a foot into the field with a mechanical head for an Elk.
1. There hide is not like a whitetail, about 3 times more dense
2. Hitting large bone mass with a 2 blade expandable might led to a deflection and not a clean kill or wounded animal
3. These so much mass to go through to get to vitals
4. Fixed blade, cut on contact (muzzy phantom 125, magnus....)