.22 Rimfire Accuracy

With the recent introduction of radar technology in chronographs, more shooters are using chronographs to evaluate the performance of rimfire ammunition in their rifles. Radar-based chronographs, such as the Garmin Xero C1 Pro are compact, easy to use and quick to set up. The cumbersome sky screens of old are not used with this new technology. My Garmin will fit into my shirt pocket, and the data from each shooting session can be downloaded to my cell phone. Because the Garmin is so easy to use, I always chronograph rimfire ammunition when shooting for groups.

The Garmin chronograph displays each individual shot in a string of fire and calculates the standard deviation, extreme spread, the average velocity, the maximum and minimum velocities, as well as computing a kinetic energy factor. When paired with the Garmin phone App, this statistical information is transferred and stored to a cell phone while shooting. Information pertinent to a shooting session can be manually entered on the phone app as well. One thing that I especially like about the Garmin chronograph is that it seldom misses recording a shot. 

Some shooters put a lot of confidence in chronograph data while others discount it entirely. You certainly do not need a chronograph or a statistics program to determine which brand or lot of ammunition is accurate in your rifle, but for me, chronograph data gives me more confidence when comparing brands or lots of ammo in my silhouette rifle. Chronograph data also helps me better understand why a certain brand of ammunition does or does not shoot well in one of my rifles. Chronograph data alone, however, is not a definitive factor in the process I use when evaluating rimfire ammunition.

I am not a statistician, but I have taken a couple of college level statistics courses. My job up until my retirement in 2019, involved conducting agricultural research trials, and I was always required to provide a statistical analysis in the trial report summaries. Although statistics can be very useful in evaluating accuracy potential of .22 rimfire ammunition, it can also lead to drawing erroneous conclusions as well. Mark Twain wasn’t too far off when he described statistics as “There are three kinds of lies: lies, damn lies, and statistics.” 

For this article, I used a couple of online ballistics tables to generate bullet drop information at different velocities and distances. The ballistic coefficients I used in developing charts were obtained from the ammunition manufacturer’s website. There are two kinds of ballistics, external and internal. External ballistics refers to factors that affect bullet flight after exiting the barrel until it reaches the target. Internal ballistics refers to factors that affect the bullet from chambering a cartridge right up until the bullet exits the barrel. It is easy to measure external ballistics but not so easy to measure internal ballistics. It is critical to keep in mind that internal ballistics can have a tremendous effect on external ballistics as well as accuracy. When internal ballistics become a factor, it can be difficult to make sense of external ballistics data. 

For what it’s worth, all companies that manufacture “match grade” rimfire ammunition use statistics to determine which ammo will be in their premium lines. For example, Lapua’s premium rimfire ammunition includes X-Act, Midas+ and Center-X, and it is produced on the same equipment from the same components in the same production run. The final determination as to which “brand” the ammunition is assigned in a production run is determined using statistical analysis (chronograph data) and evaluating the groups that were achieved from shooting in a controlled environment. The same goes for Eley’s premium brands: Eley 10X, Eley Match, and Eley Team. I have asked Lapua what statistical criteria they use when separating their three premium brands and I was told this information was a trade secret. Evidently, there is a high level of confidence in the data these companies use to separate a production lot into three different brands because the ammunition is priced accordingly; potentially the most accurate ammo being priced at a premium. 

To understand the value of chronograph data in evaluating rimfire ammunition, it is important to understand how statistical formulas are derived. Standard deviation (Sd) is a statistical measure that indicates how much individual data points (shots) in a set (string of fire) differ from the mean (average velocity of all shots) of that set. A low standard deviation means that data points are close to the average mean (average velocity), while a high standard deviation indicates they are spread out over a wider range. To obtain accurate Sd information, the more shots fired across a chronograph to determine the Sd, the more accurate the Sd information will be. In my testing, I shoot 10-shot groups for each brand or lot of ammunition, and each of the 10 shots is chronographed. I also test and chronograph ammunition over several shooting sessions before I draw conclusions on accuracy potential. If the statistics are reasonably close from one shooting session to another, I have a high confidence level that the ammunition has accuracy potential even if my group size from one session to the next isn’t the same. Before selecting a particular brand of ammunition as my match ammunition, I will shoot groups and chronograph at least five or six times at 100 meters. If it passes “inspection” at 100 meters, testing is then conducted at the range on swinger targets at 150 and 200 meters. 

It is logical to assume that the less variability there is from one shot to the next, the more accurate the ammunition will be. This may or may not be the case. Why is it that a particular brand of ammunition does not shoot tight groups when the ballistic information is really good? This can be attributed to one of three things: the shooter, the environment, or internal ballistics. Ammunition that has good ballistics but marginal accuracy will be re-tested until I am reasonably sure that shooter error and environmental factors are not contributing to substandard accuracy. There are some things that do not always make sense, so you just accept it and move on. In general, however, I have found that the most accurate rimfire ammunition in my rifles always has a low standard deviation; however, not all ammunition with a low standard deviation shoots well in my rifles. 

So, what is considered to be a low standard deviation for rimfire ammunition? The most accurate commercially “available” rimfire ammunition in my silhouette rifle is RWS R-100. It has consistently produced Sd’s between 3.5 and 7.3. However, Midas+, Center-X, and Eley Semi Auto Benchrest Precision ammunition will produce comparable accuracy with Sd’s in the 6.9 to 9.0 range. I have found that Sd’s between 3.5 and 9.0 are where the high performance Lapua, RWS, and Eley ammunition will generally fall. Not always, but most of the time. 

It is important to remember that when using chronograph data, you are not only evaluating the ammunition but also the rifle’s barrel as well. When considering group sizes, the shooter’s marksmanship skills are also a factor. I own three .22 rimfire silhouette rifles; all have “match grade” quality barrels. The exact same lot and brand of ammunition when shot in each of those three rifles will produce completely different Sd values, and sometimes the differences from one rifle to the next can be quite large. The only way to isolate the shooter and environmental conditions from the ammunition is to use a machine rest and shoot in a windless environment such as a test tunnel. Both Lapua and Whidden Gunworks offer such controlled environments for testing rimfire ammunition. Shipping a rifle (barreled action) for accuracy testing is becoming more of an option due to the scarcity of quality rimfire ammunition. Both Whidden Gunworks and Lapua have ammunition on hand, as well as different lots of the same brand of ammunition available for purchase based on the test results. For me, testing rimfire ammunition is fun and just part of the process. I prefer to do my own testing, and I do a lot of it. In addition, shooting groups improves my marksmanship skills. 

Other than group size, the extreme spread in velocity is something that I examine closely. Extreme spread is the maximum velocity minus the minimum velocity in a string of fire. When comparing brands of ammunition, it is not at all unusual for one brand of ammunition to have a lower standard deviation than another, yet the extreme spread can be greater. This is due to the way the mathematical formula is calculated to determine standard deviation. Extreme spread becomes more important as distance to the target increases. Shot to shot variance in velocity affects bullet drop as well as bullet drift caused by wind. However, at the distances we shoot, bullet drop is not as much of a factor as you might think (in a windless environment). To illustrate this point, I used ballistics tables and published ballistic coefficients for the three major brands of high performance rimfire ammunition to determine bullet drop based on velocity. I referenced a couple different ballistic apps to generate the data for bullet drop. There are a couple of ways to calculate bullet drop. One is to calculate bullet drop from the muzzle to the target; the other is to calculate the bullet drop when the rifle’s zero is set at or close to the distance to the target. I chose to measure bullet drop as close to the target as the ballistics app would allow. To do this, I had to select distances for the rifle’s zero slightly beyond the target for which I was generating data. For a 50-meter target, a 55-meter zero was selected in the ballistics app. For 100 meters, 150 meters, and 200 meters, the selected zero was 105, 155, and 205 meters respectively. By doing this, bullet drop was calculated as the difference in bullet drop between 50 meters and 55 meters (rifle zero), 100 meters and 105 meters (rifle zero), 150 meters and 155 meters (rifle zero) and 200 meters and 205 meters (rifle zero). Since I only wanted to compare bullet impact versus velocity, this was the most logical way to calculate drop versus distance to target versus velocity. 

The ballistic coefficient (bc) of 0.172 for all the Lapua brands (X-Act, Midas+, and Center-X) are all the same according to the Lapua website. For the premium Eley brands (10-X, Match, and Team) the bc’s were also all the same at 0.112. I have tested only one brand of RWS ammunition; the published bc is 0.136. The environmental data (relative humidity and elevation) were selected based on what would be typical or representative for my location. Wind velocity was set at zero for all velocity calculations. 

There are two ballistics tables in this article. They include bullet drop for Lapua, Eley, and RWS 100 ammunition at velocities between 1000 feet per second and 1180 feet per second for each silhouette distance of 50, 100, 150 and 200 meters. 

The data in the first table shows bullet drop for all three brands of ammunition at 50 and 100 meters. Based on the data in Table 1, it can be concluded that bullet drop at 50 and 100 meters is insignificant regardless of velocity variations. Regardless of the ammo, bullet drop is only about 0.1 at 50 meters if extreme spread varied from 1000 to 1180 feet per second. At 100 meters, bullet drop between 1000 fps and 1180 fps could be as much as 0.4 to 0.5. Although drop at 100 meters is slightly more significant, extreme spreads with these premium brands of ammunition are seldom more than 20 to 30 fps, therefore, the actual drop due to velocity at 100 meters will be relatively small. Since premium rimfire ammunition has been difficult to find, my goal is to find a cheap alternative to the more expensive ammunition for the 50-meter distance. I am not saying that all brands of ammunition will perform equally at 50 meters because that is not the case. But, if I can find a cheaper alternative that shoots well at 50 meters, I am comfortable with using lower-grade ammunition at 50 meters regardless of the Sd or extreme spread. I do not, however, consider 50-meter groups to be an indicator of accuracy potential beyond that distance. To provide more clarity, when I say “cheaper alternative” ammo, I am still referring to target grade ammunition and not ammunition that would typically be sold at Walmart. 

To discuss bullet drop at 150 and 200 meters, I have included chronograph data from one of my most recent shooting sessions (see Table 2). The first thing you will notice is that average velocity between premium brands varies considerably, a low of 1032.9 fps to a high of 1167.8 fps. I have found that most of my rifles prefer ammunition with velocities close to 1100 fps. Since general velocity data on most premium brands is known or even printed on the box of ammunition, knowing velocity data is helpful when I select ammunition for testing.

One brand of ammunition in Table 2, Federal Gold Medal Ultra Match (UM-1) was used by the American Olympic shooters in the mid-1960s. This ammunition has a dimpled primer and is probably some of the most accurate rimfire ammunition I have ever tested. I test commercially available brands of ammunition against UM-1. The UM-1’s standard deviation was 3.2 and the extreme spread was 9.6 and this is about as good as it gets. If any commercially available ammo produces statistics close to UM-1, my interest is definitely piqued, and I will test such ammo extensively. 

Of the ammunition listed in Table 2, those averaging one-inch, 10-shot groups (or close to that) were: Lapua Center-X, RWS R-100, Midas M (unavailable), Federal Ultra Match UM-1, Lapua Long Range and Eley SA Benchrest Precision. Eley 10-X had very good statistics but groups achieved were in the 1.5 MOA range. Even with varying standard deviations and extreme spreads, accuracy at 100 meters was nearly the same.

Bullet drop at 150 and 200 meters can be found in Tables 3. You can take any of the extreme spread data listed for ammunition in Table 2 and calculate the amount of bullet drop due to velocity alone. The bottom line is: bullet drop is much less than you might think if you are shooting in a windless environment. At 150 meters, the time of flight of a bullet from muzzle to target at 1040 fps is 0.55 seconds and .53 seconds at 1070 fps. That is not enough time difference to significantly affect bullet drop. That is assuming there is no headwind or tailwind. But there is always wind, right? Yes, and wind is the “fly in the ointment” when it comes to the effect of extreme spread on accuracy.

Before discussing the effect of velocity on wind drift, I believe it is important to establish reasonable expectations for the level of accuracy that is achievable with rifles that have an exposed hammer and are equipped with an 8 to 10 power scope. I read about rimfire competitors who shoot .5 MOA in other shooting disciplines. I don’t doubt that rifles with an in-line firing pin, higher-powered scopes and heavy barrels can achieve .5 MOA. But, with the rifles we shoot, 1 MOA at 100 meters and beyond is what I consider a very high level of accuracy. At least, 1 MOA is the upper end of what I can achieve. So, the examples of test targets that I include in this article are actual groups with no doctoring to make them appear better than what they really are. And sometimes, I have a couple of fliers in my groups that open a 1 MOA group to 1.25 to 1.5 MOA. In such a case, I discount known fliers when evaluating rimfire ammunition.

Table 4 shows wind drift at varying velocities. In extracting this data from ballistic tables, there were constraints when it came to getting the data I was looking for. So, there are two wind drift categories in this table. Both are for wind that blows from 9 o’clock to 3 o’clock at 2 mph and 10 mph. The figures in the table represent the MOA required to bring the rifle back to zero. Admittedly, the numbers in the table seem to be greater than expected, however, this is the information I got from the ballistics tables. Since we are just looking at relative differences, these figures will still prove the point that as velocity of the bullet increases from shot to shot, there is a dramatic difference in the MOA required to bring the rifle back to a zero. Which means, a low extreme spread is the most important factor when it comes to selecting accurate ammunition. 

Comparing the ammunition that produced the highest extreme spread (Midas+) to that produced the lowest extreme spread (UM-1) illustrates this point. The extreme spread for Midas + was 33.3 feet per second. With a 10-mile per hour crosswind blowing from 9 o’clock to 3 o’clock, from velocity alone, there would be a 1.1 MOA difference from the lowest to the highest velocity. At 200 meters, that would open up a group approximately 2.5 inches. The UM-1 had an extreme spread of 9.8. Calculating the difference in MOA between the low velocity of 1167.8 to the high velocity of 1172.3, there would be zero difference in MOA between the two. So, in this example, there is a 2.5-inch advantage due to ammo alone. 

In a recent shooting session, the wind was forecast to be calm and generally below 5 mph. I went to the range and started shooting groups and chronographing ammunition. The wind started out relatively calm, but the winds were just a little on the gusty side, if you could call wind velocity variations from 0 to 3 mph gusty. I was pretty much ignoring the wind and shooting. After shooting just a couple of 10-shot groups, I was disappointed in the ammo performance (see photo 1). The Eley Semi Auto Benchrest Precision ammunition I was shooting will generally hold close to one MOA at 100 meters. On this day in seemingly calm conditions, my group was 1½ inches tall and 1 ¾ inches wide. This relatively small amount of wind variation was having a much bigger effect on the size of my groups than I expected. About that time the wind started picking up, albeit it was a small increase, gusts between 2 and 6 mph. I shot the same lot and brand of Eley Ammunition after wind had picked up and my group was 1-inch tall by 3¾ inches wide. 

In addition to evaluating ammunition performance, chronograph data can show you something else. If you do extensive testing with the major brands of premium rimfire ammunition and get good statistical data but poor groups, the problem lies with the shooter, the environment or the barrel (internal ballistics). I recently had such a rifle. It would shoot only one or two brands of ammunition extremely well. It just so happened that the brands of ammunition that it shot well have been unavailable for quite some time now. I sent the rifle off and had it re-barreled. Chronographs are helpful, but the groups on paper are definitive.