500 Grains is right

lions have a highly developed central nervous system and do not like the shock waves set up by a high velocity bullet, of course any of the large N.E calibres will kill one if correct bullet placement is exhibited, but they will kill quicker with higher velocity, again bullet placement is naturally vital.

John Taylor found that of all the calibres he used for lion the .416 Rigby, mainly a magazine round, provided excellent results with its combination of frontal area and velocity.

Karl Larsen however preferred a .600 N.E with large blue nosed soft bullets which he described as capable of splitting open a lions head, maybe a little poetic licence there but he did record the feat ofkill seven lions with 9 rounds in 2 minutes, not a high velocity round by any means but I imagine the incredibly large frontal area made up for lack of speed.