For those curious about the difference between the two 8×58 cartridges, I am taking advantage of the generous permission we got from QuickLOAD's distributor to make occasional posts using that program's data.
I took a look in QuickLOAD, the interior ballistics program, and concluded the best powder for the most common bullet weight (196-grain jacketed bullet) was likely to be Vihtavuori N130. The trick is to find a powder for which the starting load (the lowest level charge you start with before working up while watching for
pressure signs; your manual will cover this) fills the space in the case under the bullet by at least 70% (aka, the loading density). Below 60%, some powders start getting erratic in pressure, and 70% is usually used instead to add a margin of safety and allow for transportation vibration to compact it some. At the other end of the equation, you don't want a powder that won't burn reasonably well at the low pressure you have, so I didn't want to see too much unburned powder at the end of the firing event. N130 looks like a good compromise.