The origins of this .450 Rigby round had been mulling around in Paul Roberts mind for some time before 1993. In 1987 Arthur Chamberlain had had poor experience on buffalo using a bespoke .458 Winchester Magnum with factory ammunition and discussed with Paul Roberts the way to rectify the problem. The .458 Winchester just lacked the velocity to ensure deep penetration but the worst element was that as America does not have an independent Proof House, as in the UK, manufacturers tended to download their ammunition in case pressures were too high and resulted in an accident. Which in America is usually followed by a law suit. The original ballistics of the .458 Winchester were set to match those of the venerable Rigby 470 NE at 2150 ft. But frequently .458 Winchester Magnum commercial ammunition was far slower than this. Paul's suggestion was to revive the old name of the .450 Rigby but in a new design based upon a necked up 416 Rigby case. This was considered and Paul offered to call it the "Rigby 450 AC". and to stamp the cases as such. The downside however was that the much larger diameter of the 416 parent case meant that the magazine would only take 3 cartridges. Arthur Chamberlain wanted a 5 shot box and this was only achievable with a necked up full length .375 Holland & Holland case. So the project was converted into a .458 Lott. He sourced the reamers from USA and Rigby rebuilt the rifle into a Lott. This was proofed in London and was a great success in the field usually requiring only one shot on buffalo. So much so that Paul Roberts then built a .458 Lott for his own personal use. 