Zero Distance With a Tall Optic Mount: 50/200 vs 36/300 vs 100 Yards

Start by measuring your own sight height. It is the distance from the center of the bore to the center of the scope tube or the sight window. A quick way is to measure from the center of the muzzle to the center of the front lens of your scope, or to the center of the sight window, with a ruler or calipers. Our LPVO mount height guide covers common heights. Enter the measured number in your ballistic app, because a wrong sight height spoils every number after it.

Why are there two zeros? Because the barrel points slightly upward relative to your line of sight. The bullet leaves the muzzle below the line of sight by your sight height, climbs across it at the near zero, rises to a peak, and falls back across it at a far zero. A 50 yard zero is really a near zero with a far zero somewhere past 200 yards. The taller the sight, the more the barrel has to angle upward, so the bullet climbs higher and takes longer to come back down.

Here are the computed numbers for the 2.6 inch sight height with a 50 yard zero. The bullet is 2.0 inches low at 10 yards and 1.2 inches low at 25. It is 1.4 inches high at 100, 1.6 high at 150 and 0.3 high at 200. It is 2.6 inches low at 250, 7.4 low at 300 and 23.6 low at 400. The highest point is 1.7 inches at 131 yards, and it crosses the line of sight again at about 207 yards. That is where the 50/200 label comes from.

Now the 3.4 inch sight height, also on a 50 yard zero. The bullet is 2.6 inches low at 10 yards and 1.6 low at 25. It is 2.2 high at 100, 3.2 high at 150, 2.7 high at 200 and 0.6 high at 250. Then it is 3.4 low at 300 and 18.0 low at 400. The peak is 3.2 inches at 159 yards, and the far crossing is at about 259 yards. Same rifle, load and zero: the taller mount alone moved the far zero by about 50 yards and the mid-range rise from under 2 inches to over 3.

To get a true 200 yard far zero, the near zero has to change. With these assumptions it comes out at about 31 yards for a 1.5 inch sight height, 52 yards for 2.6 inches and 68 yards for 3.4 inches. At 3.4 inches and a 68 yard zero the bullet is 1.9 inches low at 25 yards, 0.9 high at 100, 1.1 high at 150 and 0.1 low at 200. It is 7.6 low at 300 and 23.5 low at 400, with a peak of 1.2 inches at 134 yards. That is nearly the same shape as the 2.6 inch 50 yard zero. Few ranges have a 68 yard line, which is why many people compromise at 50 or 100.

Now 36/300. With the 2.6 inch sight height, a 36 yard zero crosses again at about 274 yards, not 300, and rises 4.2 inches at its peak around 161 yards. With 3.4 inches, a 36 yard zero crosses at about 338 yards and rises 7.4 inches around 196 yards. To get a 300 yard far crossing with these assumptions you need a near zero of about 33 yards at 2.6 inches and 42 yards at 3.4 inches. A 7 inch rise is a lot for small targets. Treat 36/300 as the label for one setup, not a rule, and on a tall mount expect a bigger rise than the label suggests.

Velocity moves the far zero as much as height does. Keep the 2.6 inch sight height and the 50 yard zero, and change only the muzzle velocity. At 2,600 feet per second the second crossing falls to about 170 yards and the bullet is 12.8 inches low at 300. At 2,900 it is 207 yards and 7.4 inches low. At 3,100 it is 232 yards and 4.7 inches low. Those velocities are illustrations: a shorter barrel or a lighter load sits toward the slow end, a longer barrel or a hotter load toward the fast end. Check your own with a chronograph and a real target.

Now the 100 yard zero. At 2.6 inches the bullet is 1.5 inches low at 25 yards, on at 100, 2.6 low at 200, 11.8 low at 300 and 29.3 low at 400. At 3.4 inches it is 2.1 low at 25, on at 100, 1.8 low at 200, 10.2 low at 300 and 26.9 low at 400. The bullet never rises more than a fraction of an inch above the line of sight, so inside 100 yards only the close-range offset matters.

That close-range offset is the real cost of a tall mount. At 10 yards the bullet strikes 2.1 inches low with the 2.6 inch sight height and 2.9 inches low with the 3.4 inch one, on a 100 yard zero. For a rifle used inside a room or at a 25 yard bay, that is the figure that matters, and it tracks your sight height. Past 100 yards the height over bore stops mattering much. At 300 yards the two sight heights differ by 1.6 inches on a 100 yard zero, about half a MOA. At 400 yards they differ by 2.4 inches, about 0.6 MOA.

This is why long-range shooters still zero at 100. A 100 yard group is easy to read, and wind and bullet drop have little time to disturb it. The turret or reticle then handles everything past that. In MOA, 11.8 inches at 300 yards is about 3.8 MOA, and 29.3 inches at 400 is about 7.0 MOA. In mils, the same drops are about 1.1 and 2.0 mil. Remember that 1 MOA is about 1.047 inches at 100 yards, and 0.1 mil is 0.36 inch. A ballistic solver takes your sight height, muzzle velocity and bullet data and gives the dial or hold for each distance from that one 100 yard reference.

So how do you choose? Use a 100 yard zero if you shoot past 200 yards, use a mil or MOA reticle or turrets, or just want one number that is easy to confirm. Use a 50 yard zero on a standard mount if most shots are inside 200 yards and you can accept a 1.7 inch rise. With a tall mount, either accept a 3 inch rise, or move the near zero out to about 68 yards if you want a 200 yard second crossing. Whatever you choose, shoot it at 25, 50, 100 and 200 yards and write down your own numbers. A computed table is a good start, but your target tells you the truth.