Hi whip, in the first part of the test @15yds he said he was shooting at the center of the target and then shot lower.
Any skilled shooter with the 1851 will easily produce a 2" or smaller group @25yds from a rest. The best mod to achieve a good sight picture is to open up the rear hammer sight. Ten seconds with a dremel does the trick.
BTW, one doesn't need a tricked out 1851 to have an accurate revolver. Many shooter always blame the gun when it's always them for the poor accuracy. The secret is practice, practice, and practice even more. My BP revolvers shoot more accurately than most of my more expensive modern handguns. I am always the weak link.
Regards,
Richard