G23 shooting low

[rolado]

My son and I recently purchased a G23 and a G23c, and both shoot several inches low. would a 6.9mm rear sight fit or do I need an adjustable rear sight?

[JR]

All the Glock rear sights are based on the same overall size. The part that changes between them is the depth of the notch.
The G23 is usually issued with a 6.5 rear sight so the 6.9 should provide about 3 more inches of elevation.