Alan I did not want to answer but feel I had to raise a few issues, you being a bloke that likes to read why?
Judging results based on horizontal performance is not good sense and discriminatory IMO. Most shooters have to accept the barrel the gunsmith gives them.
You be the judge.
Muzzle Oscillation and Lift
A node has different forms and to a fair extent, is a subset of a low frequency vibrations in rifles but not always, due to extraneous stresses. Let’s assume a harmonic pattern. If the muzzle has an oscillation pattern ratio of 1:1 as the projectile exits i.e. its vertical movement is the same as its horizontal movement then the node pattern will be round. On the other hand, if the muzzle pattern strings shots, it means that ratio is different e.g. 1:2 which has more horizontal than vertical in the nodal pattern. An example in this pattern can be seen in ABC TV logo in Australia. The latter ratio may be reversed and a barrel could toss more shots in the vertical. No amount of load development will shrink the best node because of its underlying character unless the setup is physically modified to change the ratio. But you can turn some of these nodal patterns to advantage at different ranges or learn where the rifle is limited. Depending upon the pattern produced by say a 1:2 muzzle ratio, the density of the pattern may represent a timing factor where muzzle lift of horizontal and vertical intersect and you get those super tight groups but cop an outlier when least expected. SD may reveal a bias in the expected density of the pattern, but the ES will be more representative outer of reaches of that node pattern particularly when distributions are skewed. Don’t assume they aren’t in our game. You must know your node pattern to determine what tool to use more effectively IMO, SD or ES.
It maybe that shooters have a 20% chance of getting a barrel off the shelf to perform across the course to a high-performance standard if they do not know how to modify them. Many tops shots just buy performance, buying the best gear and utilizing the best gunsmiths to minimize mechanical faults. They cry once it seems.
There are many different causes of muzzle oscillation. Some interfere with simple harmonics determined primarily by barrel length and we see distortion of the sine wave or harmonic tuning pattern. The torque factors induced by rifling comes to mind. There are many others. Varmint Al used to have some good animations such as barrel pinching on his site. In these cases, the use an OCW tune maybe better rather than a nodal tune when the barrel is in its straightest form on bullet exit. All tunes should aspire to have low SD’s and ES to perform at long distance. To change tune to a harmonic one could also involve cutting the barrel back or putting on a bloop tube and go forward or use a forward of the muzzle variable tuner. Harmonic tunes are also strictly velocity dependent so low SD and ES would be desirable. A switched-on gunsmith may also index barrels to influence the direction the node pitches or yaws the group if that is a concern. Its not the same for all shooters and is therefore discriminatory.
Shooters generally have to accept the barrel length gunsmiths supply. Then you ask yourself, does the barrel comply with harmonic barrel timing suitable for nodal tuning? Was the crown cut at the smallest diameter even if the length was right? Or did cutting the crown stuff the harmonic length? Good gunsmiths in my experience know and they learn more by following the guys who get good scores who do know.
Tighter groups can be associated with low frequencies which are expressed in the macro lift of the barrel which positive compensation can take advantage of at short range too. Shortrange benchrest barrels tend to utilise lower harmonic frequencies. Unlike short range, longer barrels have to be used to keep velocity above the transonic range or the speed of sound at long distance. Long range shooting has to fire longer strings; sometimes double and sometimes quadruple for score than short range benchrest. While a 21.75-inch barrel may have a higher stiffness ratio, its advantage may lie in the ability to complete the fundamental lift cycle associated with lower frequencies at its muzzle when the bullet exits bullet, when natural frequencies are in harmony.
To contrast that and generally speaking, in a longer barrel, a lower frequency cycle tends to complete before the bullet exits the muzzle. That means a following cycle is only partly completed at the muzzle, leaving higher frequencies as the next tune option. Higher frequencies are of course equal divisions of the lower frequencies in a natural harmonic state. This can explain the short choppiness of groups plotted to form a sine wave in some circumstances and particularly with slow burning powders. Short range benchrest utilizes a shorter rig and is easier to balance. The relationship between the bore line and centre of gravity have a bigger impact on barrel whip and vibration in our game. Getting the platform right is essential. People come in all shapes and sizes and the fulcrum point is exaggerated in our shooting style.
The underlying macro lift of the barrel still has a big influence on the distance at which that barrel performs. There are of course sections or plateaus on a plotted macro tune which can be utilised if the whole trend of groups are unfavourable and micro tunes within can be picked up. Quick Load shows different bullet barrel times associated with different frequencies. Fat stiff barrels would have to be very long to complete a full cycle of fundamental lift if that was relied upon for tune like very short barrels. Or third order frequencies on a long whippy barrel can be achieved for a suitable compensation tune if that appeals. Quick Load provides the information but you have to connect the dots with regard to barrel time and frequency.
Essentially, tune can be broken into two methods – low muzzle oscillation through stiffness or tune utilizing muzzle lift based on harmonics. Twenty-six-inch barrels are significantly stiffer than 31-inch barrels and 34-inch barrels with a back bore or bloop tube attached to a shorter barrel to make up length are more flexible. A bloop tube does influence muzzle chatter induced by an atmospheric node and it also has an impact on the seating depth because the vibrations travel up and down the barrel 4 or more times before bullet exit. There has to be a trade off with these inertia points to control group size and elevation.
Anecdotally speaking, there was an American experiment using a super thick barrel for rimfire which would not group given the velocity range that could be achieved. An element of flexibility enables the barrel to be tuned when velocity is limited. More is the case now for our gear with the imposed energy limits and lighter classes.
Shooter cases
In the Gippsland Pennant last year, I was coaching at Rosedale at 1000 yards. The shooter got a bird at 3 o’clock. I got a dark look. I did not alter on the shot because I could not see a change in conditions. The next shot went for another bird at 9 o’clock. I knew he aimed off. The following shot without change went into the centre. The same shooter, with the same gear at Lang Lang Pennant shoot at 600 yards was heading for a possible with a heap of x’s. His last shot was at 4 at 3 o’clock. Got another dark look to suggest I missed a change. I said, “Have an extra shot”, he got an x. So, I said, “We need to test this rifle at 140 yards. I want to show you something”. Sure, enough he had a horizontal group which revealed his muzzle oscillation ratio was not optimised. It was holding a tight group with an outlier at 3 o’clock. Checked it twice to reveal the same thing. I will say that a barrel can change characteristic as it heats. Another story for another time. When people say the rifle holds good horizontal ….. You just have to prove to people it comes with issues.
In another situation this year, a well-known Rosedale shooter had a relatively new barrel sour in a team’s match. To cut to the chase, I spent two days removing carbon and meticulously lapped out tight spots in his barrel. This raises two issues; one cleaning properly and the other, having the barrel slugged before chambering. I did not touch the crown or chamber. Not my job. He top scored next week.
In relation to a vertical scenario Gyro described on another thread, I just comment that the twist rate may not have been optimized to suit the variable conditions. Those Miller factors advocated in many publications fall a little short in our game. Unless we know the atmospheric density, we can drop off a node easily in free flight i.e. past the muzzle blast. That needs to be differentiated from internal ballistics chasing the node for velocity or maybe throat erosion. Its like comparing shooting in the mountains getting away with a slower twist rate than at sea level requiring a faster twist rate for gyroscopic stability. The same mountain barrel requires significant velocity increase at sea level rather than a couple of kernels to stabilize the bullet in flight as you would chasing the throat. At the other end of the scale if it is overspun, tractability becomes an issue past the overturning point in the trajectory where the nose does not follow the trajectory. In another situation, during the Commonwealth Games many years ago in Malaysia one of our blokes elevation went haywire in the afternoon. The steamy atmosphere lowered the atmospheric density, just as heat does. Here we had a combined effect. Knowledge we have now may have avoided it. Environmental conditions can be luck of the draw. Another reason to not overly penalize someone with a horizontal scoring preference. The traditional score does that anyway. Not everyone is in a position to swap barrels to suit as some do now.
Without doubt the compensation profile of the macro vibrations affects vertical spread. In a positive muzzle lift, vertical is seen at the apex of the trajectory. Yet tighten towards the compensation point further downrange before exhibiting greater spread past that point when lift becomes negative. Positioning of the load before and aft of nodal points can minimize spread or refine it further to exaggerate it to find a particular distance when the vertical paths compensate to form a tighter group i.e. slower shots are tossed higher than faster shots because they take longer to exit the barrel. Downrange gravity causes the slow shots to intersect the faster shots travelling below. With a neutral barrel, machine rest testing revealed that primer variation tended to drop shots at 6 o’clock at long range. Of course, mild positive compensation can take that variation out of primers and tight SD’s are less important. I weigh primers and Barry Davies proved to me its benefits. Good brass tends to have drilled primer pockets of uniform size and direction. Punched holes can be off centre, have furry exits and vary in diameter due to the variations in hardness of cheap brass. There are tools to fix and sort brass. Of course, computer programs assume slow shots fall lower than fast shots. Not necessarily, because it depends on barrel lift.
The old army adage is left wind lowers and right wind raises. The degree depends on twist rate and the direction of the wind in relation to bullet spin direction. This affects elevation and as my 1000-yard testing revealed in certain wind conditions may mimic a node ratio change when in fact it is an induced aerodynamic change in the terminal ballistics. At long range, groups may form ellipses if velocity does not match the prevailing conditions to optimise a changing yaw of repose based on Boatright’s theory. It can be assumed to be a bad call when it is not. In contrast to crosswinds, fishtail winds exacerbate this elevation problem depending on distance.
IMO, giving credit to horizontal elevation would be akin to handicapping a shooter. If you want to reward people for skill in wind reading perhaps one should handicap those that using higher BC bullets trying to buy a score. The correct use of velocity can make up for lack of BC.
In conclusion, I do not think it is logical to reward horizontal over vertical. Its better to learn to read wind and mirage and their effects on both the horizontal and vertical which should be the true test of skill to keep in the centre. Overtime, the gear will be the same as word gets out and is understood. Better go back to basics with technique and condition reading to catch the next train. Team shooting is a good teacher. In the future it will be up to the coaches to win, not the gear.
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