 The .458 Lott chamber will not accept an improved cartridges like the .450 Ackley Magnum and the .450 Barnes Supreme.Depending on chamber dimensions it may accept the Watts version of the cartridge.However strict SAAMI compliant chambers will not accept the .450 Watts Magnum and any attempt to discharge it in such a chamber will invariably result in higher pressures and catastrophic failures may result.