The Use of Chronographs

by
posted on November 18, 2011
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

Springfield Armory Sa35 Rifleman Review 4
Springfield Armory Sa35 Rifleman Review 4

Rifleman Review: Springfield Armory SA-35

In 2021, Springfield Armory brought out its SA-35, a rendition of the classic Browning Hi Power, one of the iconic handguns of the 20th century.

New For 2024: Smith & Wesson M&P15 Sport III

In a crowded AR-15 market, consumers are looking for the best bang for their buck. Most look no further than the Smith & Wesson M&P15 Sport, and the company has an updated generation out for 2024.

Handloads: A 10 mm Auto Loaded For Bear

The fear of a bear attack has likely sold more 10 mm Auto handguns than all firearm advertising combined. The 10 mm does deliver some impressive ballistics for a cartridge chambered in semi-automatic handguns.

The Rifleman Report: Creative Minds At Work

As all of us who experience this “mortal coil” eventually learn, the days seem more fleeting with each passing year. For those of us who make a living observing and reporting about the firearm industry, they eventually result in a somewhat disorganized pile of memories about companies, products and the people who create them.

Smith & Wesson Issues Safety Alert For Response Carbines

Smith & Wesson has identified a condition in which an out-of-battery discharge can occur when certain Response bolts fail to fully close before the trigger is pulled.

Review: GForce LVR410

With a long and storied history in the United States, lever-action carbines continue to be favorites among modern American shooting sports enthusiasts. This evaluation takes a closer look at the 24"-barreled LVR410, which is being imported by GForce Arms, Inc. of Reno, Nev.

Interests



Get the best of American Rifleman delivered to your inbox.