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Barrel Flex And Its Affect When Reloading Brass

Creating a load that produces the highest level of accuracy possible is the hope and drive of every reloader. For those on the path to greatness, at least with regards to precision loading, that creates a need to tune the ammo to your barrel. It’s a well-known fact, by both science and experience, that when a bullet enters the barrel of a gun from the chamber, the barrel is suddenly pushed into motion. This flexing of the barrel creates a wave, known as a complex sine wave, which travels the length of the gun’s barrel. Once it reaches the end, it bounces back until the wave energy is consumed by the steel in the barrel. This sine wave action isn’t centered around any single portion of the barrel, but is affected by the details of your barrel.


For a complex sine wave to be true (meaning it follows a predictable path) requires the shooter to pay attention to a few key points of the gun. First, the barrel must be installed properly to the receiver. If there is any problems with this connection, the sine wave will be dull and clunky, as well as unpredictable. If everything is installed properly, the barrel will ring like a bell. Secondly, in a perfect world, the barrel must be free floating. While not every gun is made like that, it is needful to note that anything touching the barrel along its length will negatively affect the sine wave. Thirdly, the receiver must be secured to the stock properly.

Custom stocks often attached to the receiver using a set of pillars. This method eliminates the variations in wood and some plastics due to heat and humidity. Keep in mind, wood expands when wet and shrinks when dry. This rapid expansion and regression will cause the screws that attach the stock and receiver to loosen. That’s why, to ensure the sine wave isn’t affected, it’s important to check the torque on these screws often.

Now, to the question you are asking yourself; how do we use a complex sine wave to fine tune a load to the barrel? First, let’s get an idea of what a sine wave form looks like. Hold the disassembled barrel of your rifle from your fingers and then lightly strike another metallic object against it. First, you’ll hear the ringing followed by the feel of the barrel moving in your fingers. That movement is the sine wave. You’ll notice it moves up, down, and side to side. The sweet spot is when the barrel comes back to center before going in another direction; that’s the point in which you want your bullet leaving the barrel. This means the bullet leaves the muzzle just when it is not being pushed upon by the barrel sine wave.

If the barrel is flexing upward and to the left when the bullet leaves the muzzle, the bullet (and bullet group) will be pushed that way. There are many factors that affect when the bullet leaves the barrel, such as bullet weight and the amount of powder behind it. Adding or removing just one tenth of a grain of powder can change the point in the wave where the bullet leaves the barrel. Some opt to simply adjust their scope to make up the difference, and that would be a simple fix. However, the only way to be 100% accurate 100% of the time would be to get the bullet leaving the barrel at the optimum position.

Admittedly so, the affect the sine wave movement of the barrel has on the trajectory of the bullet is often within minutes. However, for those striving for absolute perfection, finding the sine wave of your gun (through the use of slow motion cameras and experimenting with different load charges) will prove to be beneficial in the long run.