Tiger McKee

Shootrite Firearms Academy

Rifle Harmonics

When you fire a precision rifle several things occur. The barrel is forced to the rear as if a hammer has hit the end of the barrel’s muzzle, creating “longitudinal” vibrations within the barrel. The rifle itself is forced to the rear, recoiling in the opposite direction of the bullet’s movement through the barrel. This action creates a buckling effect where the barrel and receiver meet, producing “vertical” vibrations, an up and down whipping motion of the barrel. “Lateral” vibrations occur if there are any flaws in the shooter’s position, the way the stock is attached to the receiver, or inconsistencies in the bolt or the round itself. Finally, a “torsional” vibration occurs as the barrel rifling applies spin to the bullet.

For a shot to be accurate all of these actions must be consistent, everything has to be the same from shot to shot. When one factor changes the harmonics occurring as the rifle is fired are different. For example when I sling up tightly with my factory stock H-Bar AR in prone the point of impact will drop around six inches at one hundred yards. This is why rifles with free-floated barrels, with the barrel only touching at the point where it’s locks into the receiver, are more accurate than those that are not free-floating.

Ammunition is a big factor. Fire the same weight bullet but from different manufacturers and you’ll see differences in the point of impact. Switch from one bullet weight to another and you’ll have significant shifts. Even shooting the same ammo but from a different lot number can change the point of impact.

Other factors can drastically affect the bullet’s point of impact. Almost everyone has heard about not letting the barrel rest against an object while firing, but few people realize how much of a difference this makes. Let’s look at a twenty-six inch barrel Remington 700 in .308 as an example. Firing a shot from sixty yards with the bottom of the barrel resting on an object, touching at a point approximately halfway between the end of the stock and muzzle, will generally throw the bullet’s point of impact around six inches high, and normally a couple of inches to the right. As a general rule the bullet will be thrown in the opposite direction from where the barrel is making contact. Six inches high and a few inches to the side is the difference between a good hit and disaster.

Working with precision rifles requires consistency, from both the rifle and the shooter. As long as you take care of it, and feed it good ammo, the rifle will do its job. Your job is to be consistent as possible, as close to machine like as possible, doing everything the same way for each shot. You may only have one chance, one shot to solve your problem. Make sure you know exactly where that bullet is going.

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September 19, 2010 - Posted by | AR-15

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