When using a small-framed single-action revolver like the Single-Six, how you hold the grip can make a big difference in the point-of-impact. How were you holding the gun while shooting it? Were you shooting it one-handed or using a two handed grip? Freehand from a standing position or from a pistol rest on the bench? Was your grip "firm" or "relaxed".
A single-action style revolver has a tendancy to try to ride up-and-back in your hand when fired. This is even more true with a small framed, slick stocked gun like the Single-Six. The type of ammo used can also affect the "point-of-impact" since high-speed ammo will leave the barrel sooner and generally shoot to a lower point than a standard or sub-vel round will, since it will leave the barrel later (after the gun has risen slightly during recoil).
When you are checking a handgun for accuracy or "point-of-impact" in relation to point-of-aim, try using a bench rest and a two hand hold to minimize any human error.
:roll: :-D :wink: