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.
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