A 12 bore is not a good ele caliber due to shallow penetration, which arises directly from relatively low muzzle velocity combined with bullets of low sectional density.

The .700 NE is also known to be a poor penetrator. I spoke with a PH from Zim who went on a hunt where the client shot an ele in the head 4 times with a .700 NE and did not kill it. Of course all shots missed the brain. Then he grabbed the PH's .505 and killed the ele.

But back to the 12 bore, I seriously question anyone who would promote that as an elephant caliber.