Mechanical Zero: What Is It?

by
posted on January 9, 2014
** When you buy products through the links on our site, we may earn a commission that supports NRA's mission to protect, preserve and defend the Second Amendment. **
mechanical-zero_F.jpg

When it came to geometry, I used every angle possible to get out of class. Therefore, it was no coincidence I started sweating bullets during an optics seminar that went off on a mathematical tangent.

I’m glad it did, though. The technology packed into modern riflescopes may be a sine (that’s a joke for those who didn’t ditch class) of the times, but harnessing all that power still comes down to some common sense.

If you’re finicky about your setup you should find a riflescope’s mechanical zero before it is mounted. The reason comes down to geometry so basic I’d never given it any thought.

My explanation is grossly oversimplified, but it’s easy to visualize what’s going on when you look through a scope. The field of view is a circle and at its center you find the intersection of stadia lines called the crosshair.

Now, imagine the vertical line moving to the left, while the field of view remains stationary. The line becomes shorter and shorter as it moves away from the center, limiting the amount of hold over or hold under available.

When looking through a traditional scope, you always see a circle with the crosshair centered perfectly. Internally, though, the assembly that projects the image back to your eye moves slightly within the tube every time you dial for windage or elevation. Space inside is limited, so if you go far enough one way or the other the amount of adjustment available on the turrets diminishes-just like the vertical stadia line got shorter as we envisioned it moving from the field of view’s center. It’s the old “longest line in a circle must pass through the center rule” I missed because I was out with the “flu.”

So to maintain the maximum number of elevation and windage clicks available on your scope, start by finding mechanical zero before mounting. To do that, count the total number of windage “clicks” (one at a time), until you’ve gone fully from one adjustment stop to the other. Then do it again to double check your findings. Take my word for it, once you’ve hit 264 clicks it’s easy to lose count. Do the same for elevation. Don’t trust markings on the turret. Divide both in half, and that’s the respective number of clicks to dial back into the scope (from the stops). Now your reticle should be at the midpoints, mechanical zero-but if it was way off in the first place you may need to double check.

The explanation is obliquely oversimplified, I admit. And, nearly all scopes I’ve ever tested come from the manufacturer at mechanical zero.

So why invest the time? Some sporting goods employees like to make clicking noises while talking to customers, and when ballpoint pens are scarce, turrets are often used. Then there’s vibration during shipment and oversights at the factory.

The experts seem to disagree on this one, but I have a tendency to agree with the Leupold instructor at the seminar. To some degree you’ll also be lapping in those extremely small gears.

Latest

Stuart 45 Pistol Pre War Manuevers Web Main
Stuart 45 Pistol Pre War Manuevers Web Main

Guns Of The U.S. Tankers In World War II

Since the end of World War II, debates have raged about the effectiveness of American armored fighting vehicles in that conflict. Despite all the Monday morning armored quarterbacking, American AFVs were war-winners, driven to victory by some the finest fighting men our nation has ever produced.

MidwayUSA Foundation Awards Over $14 Million In Cash Grants In 2025

In honor of National Shooting Sports Month—held annually in August—along with the growing popularity of the sport with new participants, MidwayUSA Foundation announced it has distributed more than $14.2 million in cash grants to support youth shooting sports in 2025.

Making The KelTec PR57 In Wyoming

To make its PR57 handgun, KelTec invested in an entirely new manufacturing facility located in Rock Springs, Wyo. "American Rifleman Television" headed out for an inside look at the company's efficient production process.

Taurus 66 Combat: A New "Fighting Revolver"

First introduced in the 1970s, the Taurus 66 Combat is a medium-frame revolver that has seen several evolutions in its lifetime, and the latest update creates what the company considers "the final word in fighting revolvers."

Review: Taurus GX2

From cars to cellphones, as a product gets more sophisticated, it usually also gets more expensive. And, as modern handguns get more modular and optic-ready, their prices tend to go up.

Rifleman Q&A: A Garand Puzzlement

"We are a father-and-son NRA member tandem in search of an answer regarding the branding of an M1 Garand rifle. We own an M1 rifle that has markings indicating it was a “lend lease to England,” and it also has a .308 barrel/sleeve."

Interests



Get the best of American Rifleman delivered to your inbox.