What are barrel harmonics?
Harmonics is a fancy term for vibrations, and there are vibrations aplenty in the world of firearms. A firearm creates a small explosion to propel the bullet down the barrel, and everything nearby vibrates briefly because of that explosion, including the gun itself. The fastest rifle bullets in the world move at around 4,000 feet per second, but even those screamers look like chilled molasses next to the vibrations from a fired round, which move down your barrel in excess of 20,000 feet per second. As a result, there is no chance of the bullet exiting from a completely stationary and stable barrel. You can't see it, but rest assured that your gun barrel vibrates with every shot, and those vibrations are preventing your gun from achieving its ultimate accuracy.
Here's how it works. Keep things simple and pretend that your gun barrel only vibrates in a single plane, upward and downward. Minuscule variations in powder charge and bullet weight mean that no two bullets will take the exact same amount of time to travel down the barrel, so if one bullet leaves the barrel at the crest of the barrel's vibration, and another bullet leaves the barrel at the trough of the barrel's vibration, the two bullets have been fired from barrels that are not in the same position, with obvious implications for shot-to-shot consistency.
Here's how it works. Keep things simple and pretend that your gun barrel only vibrates in a single plane, upward and downward. Minuscule variations in powder charge and bullet weight mean that no two bullets will take the exact same amount of time to travel down the barrel, so if one bullet leaves the barrel at the crest of the barrel's vibration, and another bullet leaves the barrel at the trough of the barrel's vibration, the two bullets have been fired from barrels that are not in the same position, with obvious implications for shot-to-shot consistency.
However, a bullet that exits the barrel in between the crests and troughs, closer the the barrel's "true" at-rest position, experiences a different type of trouble. Once the barrel reaches the upper or lower limit of its travel (crest or trough), it has to reverse its direction. This change in direction means that, for the briefest of moments, the barrel is completely stationary, allowing a bullet that exits at that exact moment to move straight ahead (although not directly in line with the barrel's at-rest position). However, a bullet exiting the barrel during the travel time between crest and trough, though closer to the barrels at-rest position, is effectively flung out of the barrel at an angle.
This all sounds a bit dramatic, but remember that your barrel isn't wildly whipping like an unmanned fire hose. These events are taking place on an incredibly small scale, with the barrel's total travel arc measured in thousandths or even tens of thousandths of inches. However, tiny as the proportions may be, barrel vibrations can have a big effect on your accuracy. It is not at all uncommon for a 3-5 MOA rifle to become a 1-2 MOA rifle once the barrel harmonics have been appropriately addressed.
So, how then do you "appropriately address" the issue of barrel harmonics? If this phenomenon is unavoidable, what can be done to minimize the effects? There are several approaches:
This all sounds a bit dramatic, but remember that your barrel isn't wildly whipping like an unmanned fire hose. These events are taking place on an incredibly small scale, with the barrel's total travel arc measured in thousandths or even tens of thousandths of inches. However, tiny as the proportions may be, barrel vibrations can have a big effect on your accuracy. It is not at all uncommon for a 3-5 MOA rifle to become a 1-2 MOA rifle once the barrel harmonics have been appropriately addressed.
So, how then do you "appropriately address" the issue of barrel harmonics? If this phenomenon is unavoidable, what can be done to minimize the effects? There are several approaches:
Quality ammunition
Paying extra for match-grade ammunition will ensure greater consistency between rounds, increasing the likelihood of rounds exiting the barrel at similar points in the barrel's vibratory arc.
Paying extra for match-grade ammunition will ensure greater consistency between rounds, increasing the likelihood of rounds exiting the barrel at similar points in the barrel's vibratory arc.
Shorter, fatter barrels
The amount of vibration is proportional to the length and thickness of the barrel. A long, skinny barrel will vibrate much more than a short, thick barrel. In general, choosing the thickest, shortest barrel that is practical for your intended use will yield the best accuracy. Type "unlimited class railgun" into an internet search engine to see this notion taken to the extreme.
The amount of vibration is proportional to the length and thickness of the barrel. A long, skinny barrel will vibrate much more than a short, thick barrel. In general, choosing the thickest, shortest barrel that is practical for your intended use will yield the best accuracy. Type "unlimited class railgun" into an internet search engine to see this notion taken to the extreme.
Free-floating
If you don't dampen the vibrations by pretensioning (bedding) the barrel, it is best to let the barrel vibrate naturally by ensuring the barrel does not touch the stock/handguard at any point along its length, leaving the barrel "free-floating". Uneven pressure or contact between the barrel and stock/handguard can throw a serious wrench into the physics of the barrel's vibration, resulting in erratic groupings and generally reduced accuracy.
In general, free-floating provides the best accuracy for thick barrels, which are inherently rigid, whereas bedding is preferred for thin barrels.
If you don't dampen the vibrations by pretensioning (bedding) the barrel, it is best to let the barrel vibrate naturally by ensuring the barrel does not touch the stock/handguard at any point along its length, leaving the barrel "free-floating". Uneven pressure or contact between the barrel and stock/handguard can throw a serious wrench into the physics of the barrel's vibration, resulting in erratic groupings and generally reduced accuracy.
In general, free-floating provides the best accuracy for thick barrels, which are inherently rigid, whereas bedding is preferred for thin barrels.
Bedding
Vibrations can be kept to a minimum by supporting the barrel along its length or applying steady upward pressure at a single point. This can be done by carefully fitting the stock forearm around the barrel or inserting a spacer, procedures which are known as "bedding". Bedding provides the best accuracy for thin barrels, whereas free-floating is the preferred procedure for thicker, heavier barrels. Note that bedding cannot be accomplished with two-piece stocks.
Note:
Rifles with barrels that are not free-floated often shoot more accurately off-hand when the shooter's forward hand grips the magazine well or receiver, and the rifle sling (if present) is allowed to hang loosely. This method of gripping the rifle removes as much pressure from the barrel as possible to allow the most "natural" vibration, in essence creating a field-expedient free-floating barrel that provides better consistency than potentially uneven pressure from the shooter's grip. However, some shooters find that the extra stability offered by a properly braced rifle sling provides equal or better accuracy to this free-floating grip.
Vibrations can be kept to a minimum by supporting the barrel along its length or applying steady upward pressure at a single point. This can be done by carefully fitting the stock forearm around the barrel or inserting a spacer, procedures which are known as "bedding". Bedding provides the best accuracy for thin barrels, whereas free-floating is the preferred procedure for thicker, heavier barrels. Note that bedding cannot be accomplished with two-piece stocks.
Note:
Rifles with barrels that are not free-floated often shoot more accurately off-hand when the shooter's forward hand grips the magazine well or receiver, and the rifle sling (if present) is allowed to hang loosely. This method of gripping the rifle removes as much pressure from the barrel as possible to allow the most "natural" vibration, in essence creating a field-expedient free-floating barrel that provides better consistency than potentially uneven pressure from the shooter's grip. However, some shooters find that the extra stability offered by a properly braced rifle sling provides equal or better accuracy to this free-floating grip.
Tension sleeves
Another method of pretensioning a barrel is to install a sleeve around the barrel and then tighten a specially-installed nut on the muzzle against the sleeve. This exotic setup is extremely uncommon and expensive, but has been reported to produce excellent results.
Another method of pretensioning a barrel is to install a sleeve around the barrel and then tighten a specially-installed nut on the muzzle against the sleeve. This exotic setup is extremely uncommon and expensive, but has been reported to produce excellent results.
Vibration tuners and barrel weights
Various theories and procedures have been invented over the years to allow a shooter to tune their barrel's harmonics to match a particular bullet load. Some devices provide a moving pressure point between the barrel and stock that can be adjusted to tune the harmonics, other devices are simply weighted collars that are fixed to the barrel at various points. Many other methods have doubtless been developed in obscurity, but none have reached mass acceptance.
Various theories and procedures have been invented over the years to allow a shooter to tune their barrel's harmonics to match a particular bullet load. Some devices provide a moving pressure point between the barrel and stock that can be adjusted to tune the harmonics, other devices are simply weighted collars that are fixed to the barrel at various points. Many other methods have doubtless been developed in obscurity, but none have reached mass acceptance.
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