The standard big game cartridges L - R .500 Nitro Express, .470 Nitro Express, .458 Lott, .458 Winchester.

A .450 Watts short magnum was developed with the case shortened to 2.5" and loaded to more or less duplicate the British .450 Nitro Express. This latter cartridge was subsequently adopted by Winchester as the .458 Win Magnum in 1956. Mr Ackley’s loading data seems to have been a little enthusiastic for both cartridges, and the .458 Win suffered, particularly when it was found necessary to download to reduce the dangers of powder clumping. What Winchester had hoped was that their new .458 would become the industry standard to replace the host of British flanged rounds that all delivered a .450-.476 diameter bullet, weighing from 480-500 grains at a velocity of between 2125 and 2175 fps. The concept was a good one. The British double rifles were becoming too expensive, and in any case American hunters going on Safari preferred bolt actioned rifles. As Winchester intended, the .458 rapidly established itself as the new industry standard. The 500 grain steel jacketed solids gave good penetration, cheap rifles were readily available, and the .458 gave better ‘knock down’ effect on elephant than the only other viable alternative, the .404. The .450 Watts Magnum virtually died: after all, who needed more than a .458?

By the mid 1970’s plenty of people could see a reason for something more than a .458. Winchester had been forced to significantly download the .458, and terminal performance suffered. The new loads produced only around 1950fps in most sporter length barrels, and although with a good bullet penetration is usually adequate at this velocity, the old knockdown effect was noticeably less. In the meantime, Jack Lott had re-invented the wheel, so to speak, with necked up .375 cases to form a full length .450 magnum. Essentially this was the same cartridge as the much earlier Watts, but with a longer throat, and (depending on how the cases were made up) a case .05" shorter. It was Jack Lott’s version of this wildcat cartridge that became standard, since as a well known gun writer he was able to publicise it better. Professional hunters, game wardens, tsetse control officers and others who had cause to regularly shoot big game and seldom under favourable circumstances went for the .458 Lott in a big way. Its knock down effect on elephant was noticeably better than even the hottest loaded .458 Winchester. Many Professionals reckoned that the new Wildcat was superior to even the .470, and possibly as good as the .500 in terms of knock out/knock down effect. Using Softpoint bullets on lion, the .458 Lott is in a whole different class to the .458 Win due to the higher velocity and the cat’s sensitivity to hydrostatic shock (to get a proper “explosive wound” effect due to hydrostatic shock, the velocity of a bullet needs to be above 2200fps). Sensibly loaded to moderate pressures the .458 Lott will drive a 500 grain bullet at 2300fps. You can get it higher, but then sticky extraction becomes a risk on a hot day and that just isn’t worth it.

Converting a .458 Win to the .458 Lott is simple, provided the action is long enough. Many .458’s are built on standard length actions, and converting them to take a magnum length cartridge involves changing the magazine box and quite a bit of machining by a very competent gunsmith. Many .458’s are, however, built on a magnum length action and these just beg to be converted. Here conversion simply entails inserting a correct conversion reamer (note a conversion reamer cannot alter the head space unlike a poorly used chambering reamer) into the chamber and turning it until it seats. It's almost simple enough for any good home hobbyist to manage. The only catch is that the feed rails may require a little professional filing to get the longer cartridge to feed flawlessly from the magazine.