One zero is really two: near, far, and the arc between

Zero a rifle at 100 yards and you have also zeroed it somewhere around 25 — the bullet passes through your line of sight on the way up, arcs over it, and comes back through at the distance you chose. The first crossing is the near zero, the second the far zero, and the pair is a feature you can plan around, not a quirk.

Why it happens

Three things conspire to produce two crossings:

• Height over bore — the line of sight starts 1.5–3″ above where the bullet exits.

• Convergence — zeroing tilts the sight line slightly downward to meet the bullet’s path.

• The arc — the bullet climbs relative to the sight line, then gravity curves it back down through it.

A 100 yard zero, distance by distance

The high point between the crossings is the maximum ordinate. It sits roughly halfway between the zeroes, and for a 100 yard zero it is small — one to two inches. Stretch the far zero to 300 yards and the mid-range hump grows to several inches, which is the honest price of a far zero.

The classic pairs

Zero pairs are why short lanes can produce long zeroes. For a 5.56 AR-15, a 25 yard near zero rides with a far zero around 300 yards — usable hits from contact distance to 300+ while holding centre. A 50 yard near zero pairs with roughly 200 yards and keeps the mid-range hump smaller, which is why it has become the default general-purpose carbine zero.