My barrel is 725 mm from the receiver to the muzzle, it's a Badger barrel 1-18 twist. The bullet is a Steve Brooks nose pour similar in shape to the Lyman 457125. It weighs 528 gr when cast in 20-1 alloy. 
My first thought when I saw the drop in MV was that the full charge was not being consumed in the barrel and the extra powder was just producing extra muzzle flame and nothing else. Which made me ponder why that would be so when 80 gr in a 45/90 is not a heavy load. Mike Ventorino states in one of his books that the original load for the 45-1.4" Sharps was a 550 gr PP bullet over never less than 100 gr of powder, and that the cartridge was designed specifically  for long range shooting. 
Just out of curiosity I tried the 80 gr load again today only this time using CCI BR2 primers instead of the Federal GM215 M primers used in the previous load.
The results this time were.
1st shot  1226 fps
2nd        1281
3rd        1222
4th        1220
5th        1249
Average    1239.6 fps
Spread         61 fps
shots 1, 3, 4, & 5 went into a group measuring .665", shot 2, the fast one dropped 2" below the main group and about 1" to the right.
Bugger.