If you’re newer to the concept of SD, you might be wondering, “What is a ‘good’ SD when it comes to muzzle velocity?” With all that in mind, I plan to provide both ES and SD for all the data I collected – but I’ll primarily use SD when making comparisons because it is the stronger statistical measure. Often we make decisions based on truly insufficient data because the measured performance difference between two loads is simply a result of the natural variation we can expect in small sample sizes. It is very difficult to determine minor differences in velocity variation between two loads without a very large sample size (e.g.To have much confidence that our SD is accurate, we need a larger sample size than many would think – likely 20-30 shots or more. There is a tendency for SD to be understated in small samples. While it’s easy to get close to the average muzzle velocity with 10 shots or less, it’s exceedingly more difficult to measure variation and SD with precision.ES continues to grow as you fire more shots, but the average MV and SD will both begin to converge on the true value as your sample size gets larger.An over-reliance on any descriptive statistic can lead to misleading conclusions. It’s probably a bad idea to be completely dismissive of either ES or SD.ES is easier to measure but is a weaker statistical indicator in general because it is entirely based on the two most extreme events. SD is a more reliable and effective stat when it comes to quantifying muzzle velocity variations.Here are some key points from that article related to using ES or SD to quantify muzzle velocity: If you aren’t familiar with ES or SD, I’d highly recommend you go read “ Muzzle Velocity Stats – Statistics for Shooters” so you’ll be able to get the full value from this article. One of those articles dives into this specific topic and has lots of visuals and explains it in a way that you don’t have to be a math-nerd to understand. This topic in particular is exactly why I dedicated time to write the “Statistics for Shooters” 3-part series. If you’re math-averse, please stick with me! This is important, and understanding the basics can seriously help as a shooter. A low SD indicates all our velocities are closer to the average, while a high SD indicates the velocities are spread out over a wider range. Standard Deviation (SD): A measure of how spread out a set of numbers are. Extreme Spread (ES): The difference between the slowest and fastest velocities recorded.When shooters talk about muzzle velocity variation they refer to either Extreme Spread (ES) or Standard Deviation (SD). To learn more about how much consistent muzzle velocity matters in terms of hit probability at long-range, read How Much Does SD Matter? Quantifying Muzzle Velocity Variation: ES & SD We should also remember that the simulated shots and hit probability above assumes that our firing solution is absolutely perfect and we also broke the shot exactly where we should have. The diagram below shows a shot simulation and hit probability on a 20” target at 1,000 yards for a few different SD’s to give you context for how that might play out in the real world:Ī 20″ target is a pretty generous size, but you can use the visual above to estimate what would happen with a smaller target. BC), and assumes everything else was dead on. A 50 fps variation in MV would put you off-center by 14 inches! That is based on the average ballistics for all of this 6.5 Creedmoor match ammo that I test (avg. A change in velocity of just 30 fps would change your bullet drop by about 8.5 inches at 1,000 yards. Let’s start by putting muzzle velocity variation in context for long-range shooting. Often that’s how I can tell how experienced someone is in shooting long-range: Are they more concerned with getting maximum velocity or finding the most consistent velocity? I’m not saying faster bullets aren’t advantageous, but for precision long-range work that is secondary to consistent velocity. Many long-range shooters believe the most useful measuring stick for ammo quality is how consistent the muzzle velocity is. So it is very helpful for us as long-range shooters to understand the variation we can expect from our ammo shot-to-shot. While the goal is for each shot to leave the muzzle at precisely the same velocity, no ammo is perfect. That included 19 different brands and types of 6.5 Creedmoor ammo! This article is going to cover all the muzzle velocity data that I collected over almost 1,000 rounds fired.Ĭonsistent muzzle velocity is key for long-range shooting, otherwise, bullets that leave the muzzle faster than normal could miss high, or bullets that leave the muzzle slower could miss low. Welcome to Part 3 of the results of a massive 6.5 Creedmoor ammo field test, where I tested multiple boxes of every kind of 6.5 Creedmoor ammo that is marketed as “match” or “target” grade.
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