I have a Triumph and I think >200 yards should be pretty doable. I use a max load of BH209 with a MMP Blue HPH Sabot (50 Cal. rifle & .400 bullet) and shoot my own cast bullets (273 gr, .401) at ~2075 fps muzzle velocity. With this combination I've busted milk jugs a touch over 400 yards. In my experience wind is the wildcard, a 10 mph wind from the side can push my cast bullet 5 moa (16 inches) at 300 yards and a 295 gr .50 cal .18 BC bullet can be almost double that.

The mold comes from Accurate Molds, design 40-265S and looks like this:
[Linked Image]

What would Porter Rockwell do?