Just finished up cleaning the 500BPE Dickson and the brass I used today. Happy to report I now have at least one load that's good enough to hunt with.

I'm using 340gr .502" LRN cast bullets from Bear Creek Supply. These are made for the 50 AE or as blinkers for the 50 Beowulf or 500 S&W, but they work well, patched, in my 1882 vintage 500BPE 3" Dickson double. And they are affordable at $53 for 250 bullets.https://www.bearcreeksupplybullets.com/50-340

I'm patching these up .509-.510 using 9lb onion skin from Buffalo Arms, and an Excel template based on one Curl shared.

Original load per Dickson's records for this rifle was 4.5 drams or 123grains of C&H No6. I used 119gr of Swiss 2Fg.

Left barrel had 3 shots touching and cutting the left half of the bull. Right barrel 4" to the right of that, with two touching and one 1" higher. Elevation was dead on. Presumably I need either a bit more powder to bring these together, or lighter bullet.

For my next range trip, I'll try 122 grains of 2Fg with the same bullet/patch and also 119gr Swiss 2Fg patched to .511.

Overall a good day.