Noted Whitetail biologist Dr. James C. Kroll sets the criteria thus: 1-A bullet weighting at least 140 grains. 2-Velocity approx. 3,000 fps.
He considers the 257 marginal but acceptible.
I believe he uses a 7 mm magnum, 140 gr. bullet.
Dr. James C. Kroll does not know his ass from a hole in the ground.
If that is the criteria, I don't have a whitetail rifle. Even rifles like my 338 Federal and 9.3x62 won't kill deer since they don't meet the 3,000 fps requirement. I guess it's time to buy a magnum.
