While I do not load 8x58R, I do load the similar but slightly more powerful 8x57R 360. As Raimey indicates above, I too guide on R5 data when available but being older I have a supply of military "pull down" IMR 4895 which I use to replace R5 rather than N140. As mandated by careful handloading procedures, I do reduce the indicated load by about 10% and work back up while watching chronograph data and traditional signs of high pressure (recognizing that with "tip up" combination guns, if traditional high-pressure indicators show, they are already likely too high, so I stop if the target velocity is reached). Also, while most data above is for the 196-grain bullet, for this class of cartridges I would typically use a 170-grain bullet (I often use bullets different than .318" when the particular rifle will accept it, as indicated by the often-described test of checking the fit of the larger bullet in the neck of a fired case. When a larger bullet cannot be used, I load a 170 grain .321" bullet which has been resized to .318"). If I do start to load 8x58R ammo, I expect to load it by similar procedures, using acceptable bullets, IMR 4895, and reformed original length (2.125- 2.130") 38-55 cases and will accept the responsibility for it and will expect anyone else to accept responsibility for theirs since they would know their own equipment, components, and rifle while I would not.
Mike
