In my recent video on the Whitworth rifle, I made a rather embarrassing mistake, interpreting “figure of merit” accuracy measurements as complete group sizes. This was incorrect, and caused me to seriously overestimate the accuracy of the Whitworth. It was indeed a outstandingly accurate rifle, but not to the levels I originally stated. In actual fact, the Whitworth was capable of about 3 MOA at 500 yards; not the sub-1 MOA I originally stated.
The numbers recorded at the 1857 test of Enfield vs Whitworth were figure of merit, aka mean radial dispersion. This is the average distance from the center of a group (20-shot group, per British standards) to the point of impact. While much more involved to calculate, this type of measurement provides a more useful measure of accuracy than simple overall group size.
Thanks to John Simpson, David Minshall, and Rob (BritishMuzzleLoaders) for spotting and correcting this mistake!