I thought shooter error too, but shot off of a pistol rest and had the same results as offhand.
One thing I'd like to note is the paint on the front site is not level across the site.
Shot my buddies 44 and had a 3" group at 15yrds.

I'm going to some unique with the same bullets and see if that changes anything, also I'm new to reloading but have a friend helping me with it.

Don't limit your challenges
Challenge your limits