The U.S. Army Marksmanship Unit (USAMU) regulary publishes “how-to” articles on the USAMU Facebook page. One informative “Handloading Hump Day” article covers chronograph testing and statistical samples. We highly recommend you read this article, which offers some important tips that can benefit any hand-loader. Visit the USAMU Facebook page next Wednesday for the next installment.

Chronograph Testing — Set-Up, Sample Sizes, and Velocity Factors

Initial Chronograph Setup
A chronograph is an instrument designed to measure bullet velocity. Typically, the bullet casts a shadow as it passes over two electronic sensors placed a given distance apart. The first screen is the “start” screen, and it triggers an internal, high-speed counter. As the bullet passes the second, or “stop” screen, the counter is stopped. Then, appropriate math of time vs. distance traveled reveals the bullet’s velocity. Most home chronographs use either 2- or 4-foot spacing between sensors. Longer spacing can add some accuracy to the system, but with high-quality chronographs, 4-foot spacing is certainly adequate.

Laboratory chronographs usually have six feet or more between sensors. Depending upon the make and model of ones chronograph, it should come with instructions on how far the “start” screen should be placed from one’s muzzle. Other details include adequate light (indoors or outdoors), light diffusers over the sensors as needed, and protecting the start screen from blast and debris such as shotgun wads, etc. When assembling a sky-screen system, the spacing between sensors must be extremely accurate to allow correct velocity readings.

Statistics: Group Sizes, Distances and Sample Sizes
How many groups should we fire, and how many shots per group? These questions are matters of judgment, to a degree. First, to best assess how ones ammunition will perform in competition, it should be test-fired at the actual distance for which it will be used. [That means] 600-yard or 1000-yard ammo should be tested at 600 and 1000 yards, respectively, if possible. It is possible to work up very accurate ammunition at 100 or 200 yards that does not perform well as ranges increase. Sometimes, a change in powder type can correct this and produce a load that really shines at longer range.

The number of shots fired per group should be realistic for the course of fire. That is, if one will be firing 10-shot strings in competition then final accuracy testing, at least, should involve 10-shot strings. These will reflect the rifles’ true capability. Knowing this will help the shooter better decide in competition whether a shot requires a sight adjustment, or if it merely struck within the normal accuracy radius of his rifle.

How many groups are needed for a valid test? Here, much depends on the precision with which one can gather the accuracy data. If shooting from a machine rest in good weather conditions, two or three 10-shot groups at full distance may be very adequate. If it’s windy, the rifle or ammunition are marginal, or the shooter is not confident in his ability to consistently fire every shot accurately, then a few more groups may give a better picture of the rifle’s true average.

Preliminary Load Development and Velocities
When developing a load for ones firearm, a chronograph is a very useful tool. Naturally, it tells the bullet speed, allowing ballistic calculations for wind deflection and trajectory, as well as velocity variation. It can also be used, in conjunction with recent handloading manuals, as an indirect indicator of pressure.

Differences between individual barrels, chamber throats, and powder lots, plus many other variables, can cause results to differ from those cited in the manuals. Thus, beware the notion of a “magical high-speed barrel.”

When Velocities Raise Pressure Concerns — Suppose the manual states that their 26-inch .260 barrel achieved 2900 fps with X bullet, Y powder, Z case, and W primer. If you achieve that speed with identical components in your 26-inch barrel while using five (5) grains less powder, that should raise a red flag. Pressures may be at or near maximum in your rifle, despite the higher “maximum” charge cited in the manual. Observe for pressure indicators as discussed in your manuals, and never exceed published maximum powder charges.

When working up a potential match load for your rifle, it is wise to survey at least 2-3 current factory sources of data for your powder/bullet combination. This will give you a sense of the variations possible due to random factors. Then, beginning at a safe, listed “starting” powder charge, work your way up in increasing powder increments while shooting over the chronograph. Also, assess your brass and rifle for signs of increasing pressure.

What size powder increments should be used? This depends on the case volume and powder chosen. A 0.3 grain or 0.5 grain increase in powder charge may be significant in a .223, but of little consequence in a .300 Magnum. Faster burning powders are more sensitive to small changes in powder charge, increasing pressures more rapidly than slow-burning powders.

Chronograph Sample Sizes — Factors to Consider
How many shots should one fire to obtain an accurate velocity for each powder charge increment when loading? That depends in part on the uniformity of velocities given by your particular powder/bullet/barrel combination.

For example: a 3- or 5-shot sample gives an extreme spread (ES) of 140 fps between the high and low velocities recorded. The lack of uniformity indicates that firing 1 or 2 shots over the chronograph to check a powder charge is likely to give a wide margin of error. In such a case, larger sample sizes will give a better idea of the true, average velocity. While approaching the loading manual’s listed maximum charge, track the ascending velocities per charge increment. One may well see that as charges approach maximum, velocities may become much more uniform. Moreover, velocity gains per increment of increase often become smaller. Ideally, one won’t encounter velocity variations this large. Changing primers and/or neck tension may increase uniformity. If wide variations persist, however, a different powder may offer great improvement.

Consider this: A 2-shot scan gives double the data of a one-shot sample. A 4-shot sample gives twice the data of a 2-shot scan. Larger samples are particularly useful if there is much velocity variation in the population.

On the other hand, one might already be familiar with a particular powder/bullet combination in one’s barrel. If it is known to have little variation, a 1 or 2-shot scan in the early stages while working up toward the maximum can be useful, while saving expensive bullets. As powder charges approach their maximum, some like to test accuracy while shooting over the chronograph. Although it’s a bit trickier to set up the bench, chronograph and target, this does yield more data per bullets expended. In such an instance, 5-shot or even 10-shot groups may be desirable at times.

Consider 20-Shot Sample for Long-Range Match Loads
Once one arrives at a load combination intended for competition use, one should chronograph at least a 10-shot sample. This gives a reasonable picture both of the load’s uniformity and its average velocity. For long range use, a 20-shot sample of ones finalized match load is even better. This accurately shows the uniformity of one’s velocities over time. It is more likely to reveal any rare shots that develop velocities significantly different from the average.

Thus ends Part 7 in our series on Accuracy Testing and Chronographing. Next week, we’ll conclude our section on Chronograph Testing. Until then, stay safe and enjoy the shooting sports!

Imported Ammunition Sales Decline Dramatically
Over the past year, ammunition imports declined a whopping 42.2%, from $151.2 million (in Q2, 2010) to $87.4 million (in Q2, 2011). Moreover, the sales of imported shotgun shells fell 48.7%, from $5 million to $2.5 million. Apparently, now that there is a good supply of domestically-produced ammo, shooters are buying American again. Why has this occured? Currency fluctuations may be one reason. The declining value of the U.S. dollar, combined with rising shipping costs, have caused the price of imported ammo (and reloading components) to increase substantially in the past year. That has made domestic ammo more competitive price-wise. That is good news for U.S. ammo-makers. For additional research information and historical import data, visit nssf.org/research.

Editor’s Comment: Since these are production numbers, not sales figures, it may be premature to say that American shooters are spending a lot less money on rifles, but we know that sales of AR-type “black rifles” are down significantly. There was a rush of AR “panic buying” after the last presidential election that was not sustained. We are also concerned that fewer young Americans are learning to shoot rifles, while the average age of target rifle shooters continues to climb. We need to expand efforts to get young people involved in rifle shooting and hunting.

The ATF data (from 1984-2009) reveals some interesting trends:

• Total firearms produced in 2009 topped 5.4 million, exceeding the previous high total in 1994.
• Over 3,000,000 long guns were produced in 2009, the highest quantity in the past 25 years.
• The total number of firearms sold in 2009 works out to one gun for every 57 citizens, based on the 2009 U.S. population of 305,529,237.
• After a decade-long decline, handgun production rose dramatically from 2004-2009. If trends continue, in a few more years, pistol sales could out-number long gun sales.

NSSF research has updated its 14-page Industry Intelligence Report, titled Firearms Production in the United States, with the most recent data on U.S. production of pistols, revolvers, rifles and shotguns. Additional updated data found in this report include: Annual Survey of Manufacturers figures and U.S. International Trade Commission firearm import and export figures. The report is available for free to NSSF members by logging into the members section of the NSSF website, clicking “NSSF Industry Research” and then clicking “Industry Intelligence Reports.” For more information, log on to www.nssf.org.

The Mountain states led per capita in rifle purchases and accounted for 10.7 percent of rifles sold. But the South Atlantic states’ residents buy the most rifles overall — 22% of the nationwide total. It is interesting that the Pacific states (California, Oregon, Washington) encompass 14.7% of the U.S. population, but that region accounts for only 10% of rifles and shotguns sold. On the other hand, Pacific states’ residents buy 14.2% of all handguns, the second highest figure among regions. Maybe all those crazy gun control laws in California haven’t made things any safer, and people feel the need to arm themselves.

Download Full Report on Firearm Sales by Region (PDF File)