Zeroing in a A.R.M.S 40 L Rear sight

Hi everyone, I have a A.R.M.S 40L Rear sight and a Samson Flip-up front sight on my SIG556 Rifle. Which aperture do I use to Zero rifle at 50 Yards, the small hole one,or the large hole one? I know it is a M4 Forum I also have a M4 Also. Any info will help. Thanks;)

I use the small aperture, zero at 50 yards with the point of aim being the point of impact. This seems to work well for me!