.577 Nitro.
The round is designed to take down an elephant with one shot.
Addendum:
I’ve fired a lot of weapons, but the .577 is one I’ve never tried - nor do I intend to.
Just for fun I did some technical research.
To put things in perspective, the average 30.06 rifle weighs about 8 pounds and recoils with 15 foot/pounds of rearward energy.
The .577 Nitro being fired in the video weighs 15 pounds, and recoils with 70 foot/pounds of rearward energy.