Like the original Colt Single Action Army, the Ruger Old Army front sight was deliberately made a bit too tall so that it could be "adjusted" with a file. I took a clamp-on vise with me to the range so that I could hold the gun steady whilst filing, and after every 3-shot group, I filed a bit off the top of the front sight, until I got it to shoot at point-of-aim at 25 yards.
Of course before I did that, I worked up a proper load so that the gun was shooting the tightest possible group. For my gun, a Uberti 1858 .36 calibre Navy, I use 19 grains of FFFg Swiss BP, with a .375 round ball and a wonder wad.