The Use of Chronographs

by
posted on November 18, 2011
** 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. **
wiley-clapp.jpg (3)

For over three decades, I have had the good fortune of shooting for a living. Actually I have been writing for a living, but I had to shoot in order to have something to write about. And for almost every one of those shooting sessions, I've relied on a chronograph to measure the velocity of the various loads from guns as I fired them. Although I have used most brands of chronographs from time to time, my preference has been the Oehler and Millenium brands. I mention this because I believe that a chronograph is necessary to properly evaluate ammunition and firearms.

Chronographs do more than measure the instrumental velocity of a bullet passing between the machine's start and stop screens. The mini-computer inside that little box can do a number of things, but let's stick with the systematic analysis of a sequence of velocities. In a string of 10 shots, the machine can tell you which was the fastest and the slowest, along with the difference between the two and the average velocity. But it also can tell you something called the “standard deviation” of velocities. But, what's that?

It is a statistician's index of consistency. It is a bit of an oversimplification to say it, but standard deviation (SD) is the average variation from the average score. Let's say you have two loads that each average 1,000 fps for 10 rounds. One of them has an SD of 10, the other is 20. That happens because the latter had several rounds that varied farther from the 1,000 fps norm than did the SD 10 load. In other words, the latter was less consistent. More consistency means more nearly similar paths down range and therefore, better accuracy.

I will never forget the day when I was trying a new gun from a major maker, shooting the one load that was available for it. Although both gun and ammo bore famous trademarks, the accuracy was deplorable. I was in a hurry that day and did not take the time to set up the chronograph, which was a big mistake. The shots were up and down the target at 25 yards, about 8 inches between the highest and lowest. I somehow jumped to the conclusion that the 1911-type pistol was not fitted correctly and was going into battery in a very inconsistent manner. I said so in print, which was a bigger mistake.

Had I used the chronograph, which I did in a second session, I would have seen that the extreme spread of velocities was well over 300 fps and the SD was right at 100. This much extreme spread invariably produces vertical stringing on the target. Good commercial ammo SDs are usually around 15 to 20 fps and often in single digits. It was a crappy lot of ammo and I was one embarrassed young gun writer who had to apologize—in print.

Latest

Gotw Rra Lar 22 Tactical Carbine Web
Gotw Rra Lar 22 Tactical Carbine Web

Gun Of The Week: Rock River Arms LAR-22 Tactical Carbine

This week, we're on the range with the Rock River Arms LAR-22 Tactical Carbine, a rimfire variant of the AR-15 that's designed for reliability and gives enthusiasts a way to shoot affordably.

The Armed Citizen® July 11, 2025

Read today's "The Armed Citizen" entry for real stories of law-abiding citizens, past and present, who used their firearms to save lives.

Japanese Last-Ditch Small Arms Of World War II

The crude assortment of fighting tools used by the Japanese during World War II give clues of an unprepared and unmatched last-ditch fight that ultimately lead to Allied victory.

Federal Ammunition Awards 2025 Tom Knapp Memorial Scholarships

Federal Ammunition recently awarded the 2025 Tom Knapp Memorial Scholarships to two 4-H shooting sports teen ambassadors.

2025 Optic Of The Year: Burris Eliminator 6

Even as new generation after new generation of Burris Eliminator continued to add more advanced technology and functionality, it remained odd-looking—until the launch of this year’s sixth-generation product, which is the first in the line that can mount atop a rifle using standard 34 mm scope rings.

I Have This Old Gun: Star Model B

Of the many Spanish-made firearms to emerge throughout the 19th and 20th century, one of the most recognizable is the Star Model B, largely due to its similarity to the Colt Model 1911.

Interests



Get the best of American Rifleman delivered to your inbox.