Why Standard Deviation (SD) matters and how to lower those numbers!

There are many things when shooting long range that add up to account for those handful of shots you take that end up missing the mark. With factors of wind, weapon and shooter capability, the last thing you want to worry about is your ammo being inconsistent. Some variables seem to plague shooters especially at distances that the time of flight is greater and the environmental factors now play a huge roll. Things such as your ammo are sometimes often forgot, until the machine gun of excuses (BUT….BUT….BUT….BUT…BUT) comes out and leaves the shooter shaking their head. Have you ever wondered why you have a vertical dispersion great enough to cause you to miss? That’s where the standard deviations matter. The standard deviation between shot to shot can be measured with a chronograph. What the chrono will tell you are things such as muzzle velocity, standard deviation, min and max velocity on a shot string, and extreme spread. Lets dig into the standard deviations.
This is an ideal group for any shooter. There are shooters that spend a lifetime shooting and very rarely see a 5-round one hole group. Although there are so many things that you cannot see on paper, this is the desired final product.
SD or standard deviation, is a biproduct of a few things. One of the main things, if not the actual main reason…. ANNEALING brass. The process of annealing brass is where you heat the neck of the brass to soften it to a consistent point. Every time the brass is sized in a die, the brass is being work-hardened. You have to anneal the brass to soften it back up. By annealing it allows for a very consistent neck-tension which is what holds the projectile to a desired tension. Inconsistent neck tension will result in different start pressures in the case causing a raise in shot to shot speed variations. These variations is what the chrono will display. Downrange feedback can also show you this. If you build a profile on a ballistic solver and input two muzzle velocities roughly 20FPS in variation, and then look at your bullet flight path in MOA or MILS at 1000yds, you will see the firing solution numerical value to be different. This why you want to have very consistent and low SD to include Extreme spread. (Save extreme spread for a different conversation) ANNEAL YOUR BRASS!

Starting off with the best brass is never a bad idea. The cost of Lapua brand brass is worth the investment in our opinions. Lapua brass has earned its reputation and is a no-brainer for competitive shooters because of its strength, consistency, and and life expectancy of the cases. Having extremely consistent brass such as Lapua, you will begin to see lower SD’s without even factoring in the annealing process.
standard deviations
Load development. This is a picture of a 200yd shot group using the “‘ladder test” method. This where the ammo is loaded in different charge weights going up in weight. The shot group is annotated shot to shot with a chrono. As the shots are being fired one by one, the shooter annotates where they impact on paper. There will be small groups forming in little clusters but what you’re looking for are groups where the chrono shows the lowest speed deviation, and on the downrange feedback to be the closest together. Ideal scenario, is just like this picture. 39.0, 39.3, and 39.6 are touching and only 18FPS extreme spread from the 39.0-39.6. This means after you shoot your ladder group and you identify your node, split the difference between the minimum and maximum, and there you go, 39.3 it is. A large charge weight variation, but still yielding a one hole group at 200yds. This process is proven to work well. REMEMBER, THIS IS NOT A HOW TO WITH CHARGE WEIGHTS OR MANUFACTURING YOUR AMMO. USE RELOADING MANUALS AND START LOW AND WORK YOUR WAY UP. EVERY RIFLE AND CHAMBER IS DIFFERENT. DO NOT ATTEMPT TO COPY THIS LOAD DATA.THIS IS FOR DEMONSTRATION PURPOSES ONLY FOR A LADDER TEST. YOUR SAFETY IS EXACTLY THAT. DO THE RIGHT THING. BE SAFE AND LOAD AT YOUR OWN RISK. HAPPY REOADING.

2 Comments Add yours

  1. Rick Roger's says:

    Is it best to anneal before sizing or after

    1. Mr.Wild says:

      Well for starters, there are a lot of different ways to answer this question. In my opinion, I think annealing AFTER sizing is the means to have the lowest and most consistent Ammo. More important than that, is not having brass lot sorted and having some brass on x3 fires and some on x1 without being annealed. They will have some spring back feel on the press while seating the bullet. I have found that even the fx400 won’t match even a chargemaster if it’s not in a node. All together I would say the route to success is do whatever process you do as long as annealing is in there. As vague as that is. There was a point where I was annealing after every x2 fires and getting really good SD and ES too. My buddy says annealing then sizing helps keep the brass uniform for feeding issues but I don’t see the performance on the LABradar or the magneto. The most consistent for me has been size, anneal stick a Berger in, go shoot.

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