Many years ago, I got my "leg" on the Distinguished badge shooting a .30-06 Garand with peep sights at 1,000 yards. Fun!
But I made it easy...I lined the top of the front post sight on the bottom of the target frame and the side of the front post with the right side of the target frame, and simply adjusted the sights so the bullets hit the center of the bullseye. For all other ranges, including 600 yd, I used the standard sight picture.
Wish I could still do it...but my old eyes are having trouble lining up those targets and iron sights at different distances clearly!
(But I can still handle a cross hair! I like to shoot my .22 LR Ruger Mk II pistol with 2X scope at 100-yds...get 3" groups.)