There's 2 versions of the .600 first introduced by Jeffery approx. 1900 in 2 8/10 and 3 inch. Gunmakers of that period were testing everything, but anyone with any experience with big bores will tell you the .600 3" is over-powered a tad.

I own 3 .577 Nitro's - 1 Purdey, 1 Holland, and 1 Boss, and they are the best at stopping anything you may encounter close up. It's a close range calibre for certain. I remember one hunt in where my pops shot a big nasty bull at approx. 25 yards with a Rigby .577, when the bullet hit him the mud went flying into the stratosphere and he fell straight on his belly. Pops used the only pre-war Rigby ever made in .577 - the gun is now owned by Ross Seyfried, and he will most likely be baried with it I am certain.

Here is the photo of that event. 1963c