Each Wednesday, the U.S. Army Marksmanship Unit publishes a reloading “how-to” article on the USAMU Facebook page. This past week’s “Handloading Hump Day” article, the latest in a 7-part series, relates to 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.
In this video, Bryan Litz of Applied Ballistics explains how to choose a bullet for long-range shooting and explains what you should be looking for when developing a long-range load. Bryan notes that, with a new rifle build, the bullet you select may actually dictate your gun components. When starting from a “clean slate”, once you select a bullet, you will then pick a barrel, twist rate, and cartridge that are appropriate for that bullet. In choosing a long-range projectile, Bryan recommends you choose a high-BC bullet “that is known for precision”. Then you need to find an ultra-consistent, reliable load.
This video is worth watching. Bryan Litz makes some very good points.
Load Development — Why Consistency is Key (and Half-MOA May Be Good Enough)
After choosing a bullet for your long-range project, then you need to develop a load through testing. Bryan explains: “Once you’ve selected a bullet … and you have selected the components around that bullet, the most important thing to remember in hand-loading is consistency. You’re going to do some testing to see what combination of powder charge, powder type, and seating depth give you the best groups and lowest standard deviations in muzzle velocity.”
Bryan says that if you develop a load that can shoot consistent, half-minute groups in all conditions, you should be satisfied. Bryan says that many long-range shooters “spin their wheels” trying to achieve a quarter-MOA load. Often they give up and start all over with a new bullet, new powder, and even a new cartridge type. That wastes time, money, and energy.
Bryan cautions: “My advice for hand-loaders who are long-range shooters, is this: If you can get a load that is reliable and can shoot consistent, half-minute groups with low MV variation and you can shoot that load in any condition and it will work well, then STICK with THAT LOAD. Then focus on practicing, focus on the fundamentals of marksmanship. The consistency you develop over time by using the same ammunition will mean more to your success in long range shooting than refining a half-minute load down to a quarter-minute load.”
Bryan notes that, at very long range, shooting skills and wind-calling abilities count most: “Your ability to hit a 10″ target at 1000 yards doesn’t improve very much if you can make your rifle group a quarter-minute vs. a half a minute. What’s going to determine your hit percentage on a target like that is how well you can calculate an accurate firing solution and center your group on that target. A lot of people would be more effective if they focused on the fire solution and accurately centering the group on the target [rather than attempting to achieve smaller groups through continuous load development].”
Editor’s Note: We agree 100% with the points Bryan makes in this video. However, for certain disciplines, such as 600-yard benchrest, you WILL need a sub-half-MOA rifle to be competitive at major matches. Well-tuned, modern 600-yard benchrest rigs can shoot 1/4-MOA or better at 100 yards. Thankfully, with the powder, bullets, and barrels available now, 1/4-MOA precision (in good, stable conditions) is achievable with a 17-lb benchgun built by a good smith with premium components.
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When a rifle isn’t shooting up to it’s potential, we need to ask: “Is it the gun or the shooter?” Having multiple shooters test the same rifle in the same conditions with the same load can be very revealing…
When developing a load for a new rifle, one can easily get consumed by all the potential variables — charge weight, seating depth, neck tension, primer options, neck lube, and so on. When you’re fully focused on loading variables, and the results on the target are disappointing, you may quickly assume you need to change your load. But we learned that sometimes the load is just fine — the problem is the trigger puller, or the set-up on the bench.
Here’s an example. A while back we tested two new Savage F-Class rifles, both chambered in 6mmBR. Initial results were promising, but not great — one gun’s owner was getting round groups with shots distributed at 10 o’clock, 2 o’clock, 5 o’clock, 8 o’clock, and none were touching. We could have concluded that the load was no good. But then another shooter sat down behind the rifle and put the next two shots, identical load, through the same hole. Shooter #2 eventually produced a 6-shot group that was a vertical line, with 2 shots in each hole but at three different points of impact. OK, now we can conclude the load needs to be tuned to get rid of the vertical. Right? Wrong. Shooter #3 sat down behind the gun and produced a group that strung horizontally but had almost no vertical.
Hmmm… what gives?
Shooting Styles Created Vertical or Horizontal Dispersion
What was the problem? Well, each of the three shooters had a different way of holding the gun and adjusting the rear bag. Shooter #1, the gun’s owner, used a wrap-around hold with hand and cheek pressure, and he was squeezing the bag. All that contact was moving the shot up, down, left and right. The wrap-around hold produced erratic results.
Shooter #2 was using no cheek pressure, and very slight thumb pressure behind the tang, but he was experimenting with different amounts of bag “squeeze”. His hold eliminated the side push, but variances in squeeze technique and down pressure caused the vertical string. When he kept things constant, the gun put successive shots through the same hole.
Shooter #3 was using heavy cheek pressure. This settled the gun down vertically, but it also side-loaded the rifle. The result was almost no vertical, but this shooting style produced too much horizontal.
A “Second Opinion” Is Always Useful
Conclusion? Before you spend all day fiddling with a load, you might want to adjust your shooting style and see if that affects the group size and shape on the target. Additionally, it is nearly always useful to have another experienced shooter try your rifle. In our test session, each time we changed “drivers”, the way the shots grouped on the target changed significantly. We went from a big round group, to vertical string, to horizontal string.
Interestingly, all three shooters were able to diagnose problems in their shooting styles, and then refine their gun-handling. As a result, in a second session, we all shot that gun better, and the average group size dropped from 0.5-0.6 inches into the threes — with NO changes to the load.
That’s right, we cut group size in half, and we didn’t alter the load one bit. Switching shooters demonstrated that the load was good and the gun was good. The skill of the trigger-puller(s) proved to be the limiting factor in terms of group size.
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When a rifle isn’t shooting up to it’s potential, we need to ask: “Is it the gun or the shooter?” Having multiple shooters test the same rifle in the same conditions with the same load can be very revealing…
When developing a load for a new rifle, one can easily get consumed by all the potential variables — charge weight, seating depth, neck tension, primer options, neck lube, and so on. When you’re fully focused on loading variables, and the results on the target are disappointing, you may quickly assume you need to change your load. But we learned that sometimes the load is just fine — the problem is the trigger puller, or the set-up on the bench.
Here’s an example. A while back we tested two new Savage F-Class rifles, both chambered in 6mmBR. Initial results were promising, but not great — one gun’s owner was getting round groups with shots distributed at 10 o’clock, 2 o’clock, 5 o’clock, 8 o’clock, and none were touching. We could have concluded that the load was no good. But then another shooter sat down behind the rifle and put the next two shots, identical load, through the same hole. Shooter #2 eventually produced a 6-shot group that was a vertical line, with 2 shots in each hole but at three different points of impact. OK, now we can conclude the load needs to be tuned to get rid of the vertical. Right? Wrong. Shooter #3 sat down behind the gun and produced a group that strung horizontally but had almost no vertical.
Hmmm… what gives?
Well each of the three shooters had a different way of holding the gun and adjusting the rear bag. Shooter #1, the gun’s owner, used a wrap-around hold with hand and cheek pressure, and he was squeezing the bag. All that contact was moving the shot up, down, left and right. Shooter #2 was using no cheek pressure, and very slight thumb pressure behind the tang, but he was experimenting with different amounts of bag “squeeze”. His hold eliminated the side push, but variances in squeeze technique and down pressure caused the vertical string. When he kept things constant, the gun put successive shots through the same hole. Shooter #3 was using heavy cheek pressure. This settled the gun down vertically, but it also side-loaded the rifle. The result was almost no vertical, but this shooting style produced too much horizontal.
A “Second Opinion” Is Always Useful
Conclusion? Before you spend all day fiddling with a load, you might want to adjust your shooting style and see if that affects the group size and shape on the target. Additionally, it is nearly always useful to have another experienced shooter try your rifle. In our test session, each time we changed “drivers”, the way the shots grouped on the target changed significantly. We went from a big round group, to vertical string, to horizontal string.
Interestingly, all three shooters were able to diagnose problems in their shooting styles, and then refine their gun-handling. As a result, in a second session, we all shot that gun better, and the average group size dropped from 0.5-0.6 inches into the threes — with NO changes to the load.
That’s right, we cut group size in half, and we didn’t alter the load one bit. Switching shooters demonstrated that the load was good and the gun was good. The skill of the trigger-puller(s) proved to be the limiting factor in terms of group size.
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