Gene Beggs
Active member
Several years ago, a lively discussion took place here on BR Central about barrel fluting.
Skip Otto, God rest his soul, was a strong proponent of fluting insisting it made the barrel stiffer. Many took this to mean he thought it made the barrel stronger and that's not what he meant at all. What he was referring to was the fact that fluting removes unnecessary dead weight from the barrel resulting in less gravity droop at the muzzle. Less droop means less whip when the rifle is fired, hence less vertical dispersion when out of tune.
When we speak of barrel vibration we often use the terms, frequency and amplitude.
Frequency is simply the number of cycles the barrel completes in a given period of time and is the result of length, weight, diameter, contour etc. Unless the barrel is altered in some way, (Tuners
) frequency never changes; amplitude does.
Amplitude refers to how much the barrel moves from one extreme to the other as it vibrates. Long whippy barrels vibrate at a lower frequency but with greater amplitude. (Visualize a long, cane fishing pole.) A short stiff barrel (visualize a pool cue) vibrates at a higher frequency but with less amplitude. Each barrel displays a distinct signature on the target as it goes in and out of tune. The longer, more flexible barrels show greater vertical dispersion when out of tune, but such a barrel "dwells" longer at the stops than a short stiff tube making it easier to keep in tune.
Now that we have the option of using tuners and adjusting them at the bench, we are no longer stuck with a barrel that vibrates at only one frequency; we can vary the frequency at will to compensate for slight changes in atmospheric conditions by moving a weight fore and aft on the barrel. "How much do you move the weight and in which direction?" you ask. Well, we don't move it much. With the typical BR barrel in use today we only move the weight .0180 in either direction to get the rifle perfectly in tune assuming it was totally out of tune to begin with. That's right; only .0180. "But wouldn't that depend on how much weight you are moving?" you ask. NO, believe it or not, the amount of weight does not matter within reason. Here is a good example of how it works.
Let's take for example a steel or acoustic guitar. The musician holds a small steel bar in his left hand and places the bar on the strings. As he moves the bar fore and aft the frequency/tone rises and falls; the shorter the string, the higher the pitch and vice versa. Would it matter if the musician used a four ounce, 5/8 inch bar or a one inch diameter, eight ounce piece? No, of course not; the tone/frequency would be the same in either case. It's the position of the steel on the string that makes the difference, not the weight. A rifle barrel reacts in the same manner.
Most benchrest barrels in use today are between 22 and 24 inches in length. Some are LV contour while others are HV and vary in weight from about five to six pounds. I was delighted when I discovered they all reacted exactly the same to tuners. The early, cylindrical, beyond the muzzle tuners I experimented with varied in weight from four to six ounces. I started with 20 tpi and later discovered that 28 tpi was ideal. Regardless of tuner weight, within reason, with 28 tpi, a half turn in either direction brings the rifle perfectly in tune, assuming it was completely out of tune to begin with. From one node to the next is exactly one revolution. Simple, easy, reliable.
For weight, I chose four ounces for my tuners because I knew it worked. Just exactly how little weight we could get away with; I don't know. One thing I do know; it is impractical to use more than about six ounces and remain within weight limitations with our LV and sporter rifles.
As far as weight is concerned, I have discovered that I can easily remove four ounces of weight from the last two thirds of the barrel by placing four 3/8 inch flutes at 1:30, 4:30, 7:30 and 10:30. This leaves the barrel full diameter in the vertical and horizontal plane for stiffness and results in a ZERO weight penalty with NO reduction in length. Pretty slick; huh?
Oh,,, by the way; when we get our rifle perfectly in tune, can we expect it to remain in tune throughout the day? Yes, if the density/weight of the atmosphere remains exactly the same, the rifle will remain in tune, but have you ever seen that happen? It's almost unheard of; isn't it?
Can we set our tuner and forget it expecting the rifle to shoot forever without adjustment? Of course not ! A change in outside temperature of five degrees will show a visible amount vertical dispersion on the target, a change of ten degrees will show even more and a change of twenty degrees will throw the rifle completely out of tune if we do nothing to compensate. We have two methods of compensating; one, adjust the load, two, adjust the tuner. Which do you think is easier?
Even though the tuner can easily be placed at any one of eight positions, i.e., 12, 1:30, 3:00, and so on, I rarely make adjustments of less than a quarter turn. If I'm only 1/8 turn out of tune, I know the old devil wind will hurt me far more than a half bullet hole of vertical. A perfectly tuned, laser accurate rifle will not help you with reading conditions, rifle handling, bag problems, etc. Study Ratigan's book, go to Tony's school, and get out there and practice, practice, practice.
Later,
Gene Beggs
Skip Otto, God rest his soul, was a strong proponent of fluting insisting it made the barrel stiffer. Many took this to mean he thought it made the barrel stronger and that's not what he meant at all. What he was referring to was the fact that fluting removes unnecessary dead weight from the barrel resulting in less gravity droop at the muzzle. Less droop means less whip when the rifle is fired, hence less vertical dispersion when out of tune.
When we speak of barrel vibration we often use the terms, frequency and amplitude.
Frequency is simply the number of cycles the barrel completes in a given period of time and is the result of length, weight, diameter, contour etc. Unless the barrel is altered in some way, (Tuners
) frequency never changes; amplitude does. Amplitude refers to how much the barrel moves from one extreme to the other as it vibrates. Long whippy barrels vibrate at a lower frequency but with greater amplitude. (Visualize a long, cane fishing pole.) A short stiff barrel (visualize a pool cue) vibrates at a higher frequency but with less amplitude. Each barrel displays a distinct signature on the target as it goes in and out of tune. The longer, more flexible barrels show greater vertical dispersion when out of tune, but such a barrel "dwells" longer at the stops than a short stiff tube making it easier to keep in tune.
Now that we have the option of using tuners and adjusting them at the bench, we are no longer stuck with a barrel that vibrates at only one frequency; we can vary the frequency at will to compensate for slight changes in atmospheric conditions by moving a weight fore and aft on the barrel. "How much do you move the weight and in which direction?" you ask. Well, we don't move it much. With the typical BR barrel in use today we only move the weight .0180 in either direction to get the rifle perfectly in tune assuming it was totally out of tune to begin with. That's right; only .0180. "But wouldn't that depend on how much weight you are moving?" you ask. NO, believe it or not, the amount of weight does not matter within reason. Here is a good example of how it works.
Let's take for example a steel or acoustic guitar. The musician holds a small steel bar in his left hand and places the bar on the strings. As he moves the bar fore and aft the frequency/tone rises and falls; the shorter the string, the higher the pitch and vice versa. Would it matter if the musician used a four ounce, 5/8 inch bar or a one inch diameter, eight ounce piece? No, of course not; the tone/frequency would be the same in either case. It's the position of the steel on the string that makes the difference, not the weight. A rifle barrel reacts in the same manner.
Most benchrest barrels in use today are between 22 and 24 inches in length. Some are LV contour while others are HV and vary in weight from about five to six pounds. I was delighted when I discovered they all reacted exactly the same to tuners. The early, cylindrical, beyond the muzzle tuners I experimented with varied in weight from four to six ounces. I started with 20 tpi and later discovered that 28 tpi was ideal. Regardless of tuner weight, within reason, with 28 tpi, a half turn in either direction brings the rifle perfectly in tune, assuming it was completely out of tune to begin with. From one node to the next is exactly one revolution. Simple, easy, reliable.
For weight, I chose four ounces for my tuners because I knew it worked. Just exactly how little weight we could get away with; I don't know. One thing I do know; it is impractical to use more than about six ounces and remain within weight limitations with our LV and sporter rifles.
As far as weight is concerned, I have discovered that I can easily remove four ounces of weight from the last two thirds of the barrel by placing four 3/8 inch flutes at 1:30, 4:30, 7:30 and 10:30. This leaves the barrel full diameter in the vertical and horizontal plane for stiffness and results in a ZERO weight penalty with NO reduction in length. Pretty slick; huh?
Oh,,, by the way; when we get our rifle perfectly in tune, can we expect it to remain in tune throughout the day? Yes, if the density/weight of the atmosphere remains exactly the same, the rifle will remain in tune, but have you ever seen that happen? It's almost unheard of; isn't it?
Can we set our tuner and forget it expecting the rifle to shoot forever without adjustment? Of course not ! A change in outside temperature of five degrees will show a visible amount vertical dispersion on the target, a change of ten degrees will show even more and a change of twenty degrees will throw the rifle completely out of tune if we do nothing to compensate. We have two methods of compensating; one, adjust the load, two, adjust the tuner. Which do you think is easier?
Even though the tuner can easily be placed at any one of eight positions, i.e., 12, 1:30, 3:00, and so on, I rarely make adjustments of less than a quarter turn. If I'm only 1/8 turn out of tune, I know the old devil wind will hurt me far more than a half bullet hole of vertical. A perfectly tuned, laser accurate rifle will not help you with reading conditions, rifle handling, bag problems, etc. Study Ratigan's book, go to Tony's school, and get out there and practice, practice, practice.
Later,
Gene Beggs
