Before I give you my 2 cents on your issue. On your Cape Buffalo hunt, who was the outfitter that you used? an fyi, 1.2 to 0.5 to 1.0 is not that bad.
Many years ago when I was optimizing my 300 win mag I ran into similar issues This was my first foray into reloading back in the early nineties. What I wound up doing was converting the Grains to Grams to milligrams. I suspected there was inaccuracy in my balance and the measure in grains. To verify if this would make a difference I weighed in grains each bullet, then weighed my powder charges(put these in test tubes, this was done on my Lee Balance. At the time I was managing analytical laboratories and had access to very accurate balance capable of weighing in .01 milligrams. Target at 180 grains all bullets appeared to match each other on my lee scale. When I weighed the bullets in Mg the Target 180 grains should have been 11663.81mg- what I found was there was variation that when converted back to grains the worst bullet approached 2 grains, one really bad one out of my box. It was similar with my powder charges but not as much. I then adjusted the bullet weight versus the target weight of my charge versus my target bullet weight, lighter bullet lighter charge. When I made these changes not only did my groups tighten up so did my velocity readings on my chronograph. A couple years back I found some of these reloads shot it through my rifle that has since been re-barreled. The old loads Shot exactly 1.5 " high above the bullseye exactly where it was originally three shots group about .5-.6 MOA at a 100 yards just like when they were reloaded 20 plus years ago. There was a period of time where I quit hunting and shooting, but glad I found the old reloads. I only neck sized my reloads back then. I purchased a Balance from Amazon and do things in a similar fashion these days, I do measure the length of each case and have a target length for each caliber, use better dies now. I hope that helps you.
