Barrel Indexing
- Thread starter 2D1C
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Barrel index doesn't make your gun any more accurate. What it does it change where the pellet/slug meets the rifling. That's why you get different poi. In my testing it doesn't make your gun shoot more accurate. The difference size groups are due to shooter errors, wind, hold, pellets/slug sizing and weight, etc.
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Indexing won't always make a meaningful difference to group size but sometimes it does. The concept has nothing to do with where the pellet meets the rifling, rather it deals with harmonics. Every barrel vibrates when fired, and this vibration produces some movement of the muzzle which is one of the contributors to dispersion (scattering) of pellets on target. And no barrel is perfectly straight so that produces some bias to the direction in which the forces are acting to set up this vibration.
The idea is to orient the barrel so the vibration produces a predominantly vertical signature. Why does that help? Well, here's a practical experiment suggested by Hengehold on the accurateshooter forums:
"[The idea of]indexing a barrel in a 12 o'clock or 6 o'clock position is giving it the best possible state of harmonics to start with.
To illustrate what is happening you can try an exercise with a cleaning rod secured near the handle in a vice. First, flick the end of the cleaning rod straight up-and-down and watch the pattern of movement of the tip of the cleaning rod until movement comes to a stop. Second, try flicking the cleaning rod left and right and watch the pattern of movement of the cleaning rod until the mvmt has come to a stop. You will notice that when you flick the cleaning rod in an up-and-down motion that as the cleaning rod eventually stops whipping up and down it stays in a vertical plane. However, when you flick the cleaning rod in a lateral motion you'll notice that before it comes to rest the whip pattern of the cleaning rod is lateral then circular before eventually making a vertical motion. This cleaning rod is representing the action of a barrel that is whipping while being shot. A barrel that is whipping only in a vertical plane would have only one movement to overcome. A barrel with a lateral movement would eventually have to overcome not just the lateral movement but a circular motion and eventually a vertical mvmt as you will see demonstrated with a cleaning rod."
taken from http://forum.accurateshooter.com/threads/indexing-a-rifle-barrel.3902203/
The idea is to orient the barrel so the vibration produces a predominantly vertical signature. Why does that help? Well, here's a practical experiment suggested by Hengehold on the accurateshooter forums:
"[The idea of]indexing a barrel in a 12 o'clock or 6 o'clock position is giving it the best possible state of harmonics to start with.
To illustrate what is happening you can try an exercise with a cleaning rod secured near the handle in a vice. First, flick the end of the cleaning rod straight up-and-down and watch the pattern of movement of the tip of the cleaning rod until movement comes to a stop. Second, try flicking the cleaning rod left and right and watch the pattern of movement of the cleaning rod until the mvmt has come to a stop. You will notice that when you flick the cleaning rod in an up-and-down motion that as the cleaning rod eventually stops whipping up and down it stays in a vertical plane. However, when you flick the cleaning rod in a lateral motion you'll notice that before it comes to rest the whip pattern of the cleaning rod is lateral then circular before eventually making a vertical motion. This cleaning rod is representing the action of a barrel that is whipping while being shot. A barrel that is whipping only in a vertical plane would have only one movement to overcome. A barrel with a lateral movement would eventually have to overcome not just the lateral movement but a circular motion and eventually a vertical mvmt as you will see demonstrated with a cleaning rod."
taken from http://forum.accurateshooter.com/threads/indexing-a-rifle-barrel.3902203/
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IMO and experience, nervoustrig is correct and pigeon man is wrong. Any mechanical system will have vibration. Firing an air gun causes vibration. You want the barrel to move (the harmonics) in as predictable a pattern as possible.
This barrel harmonics concept was used by many people as far back as the '70's in firearms (possibly further back but that is when I became aware of it). We would develop loads that had POI at the highest point noted and it wasn't always the highest velocity load. It was thought to be related to harmonic barrel movement and accuracy would almost always be better with those loads. If you can get your projectile (or pellet) to exit the barrel at the end of the harmonic movement cycle then you will often see improved accuracy. Why? Seemingly because the moving barrel has to slow/stop/accelerate to the other direction and spends more time in that position range than when it is moving faster in a single direction. This may produce a larger "static window" position where barrel movement could effect accuracy.
As an illustration, I'll give away one of my shooting tricks that used to impress people. Try to shoot a target thrown into the air (not with a shotgun but with a rifle or pistol). It is always pretty hard to hit. But it is MUCH easier to hit it when it reaches the apex of its movement because it is slowing, basically stopping for an instant, then accelerating back down. You have a relatively large window with a much slower moving target and you will hit it more often at that point. The barrel harmonics concept seems to be very similar.
This barrel harmonics concept was used by many people as far back as the '70's in firearms (possibly further back but that is when I became aware of it). We would develop loads that had POI at the highest point noted and it wasn't always the highest velocity load. It was thought to be related to harmonic barrel movement and accuracy would almost always be better with those loads. If you can get your projectile (or pellet) to exit the barrel at the end of the harmonic movement cycle then you will often see improved accuracy. Why? Seemingly because the moving barrel has to slow/stop/accelerate to the other direction and spends more time in that position range than when it is moving faster in a single direction. This may produce a larger "static window" position where barrel movement could effect accuracy.
As an illustration, I'll give away one of my shooting tricks that used to impress people. Try to shoot a target thrown into the air (not with a shotgun but with a rifle or pistol). It is always pretty hard to hit. But it is MUCH easier to hit it when it reaches the apex of its movement because it is slowing, basically stopping for an instant, then accelerating back down. You have a relatively large window with a much slower moving target and you will hit it more often at that point. The barrel harmonics concept seems to be very similar.
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Also, in addition to indexing the barrel for a 6 o'clock position, or a 12 o'clock position (I prefer 12), i have fitted on my Steyr barrel, that is free floating, a weight made of HDPE plastic. It's a little larger than the barrel, fit's snugly. I'll adjust the weight in 1/4" increments, from the muzzle on in, shooting several groups at each 1/4". I then pick the tightest group, and that's where the weight will live for competitive purposes. I have yet to do this process to other rifles.
Tom Holland
Field Target Tech
Tom Holland
Field Target Tech
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Seems to be 2 sides of a coin. Tune load/power to match natural barrel vibrations OR use a weight to change natural barrel vibrations to match the load/power. This has also been done in firearms. The BOSS system comes to mind although I don't have any personal experience with it.
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I once owned a Boss system custom made for a TX200. My pal, tool and die, made it and it was so well made. Sadley, POI change with dirrerent setting BUT they all were the same size. Never should have sold it because it was really something to lookat. Kinda like a micrometer sleeve, ajustments with calibration marks on the inner tube.
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