Helping Them with More Advanced Tuning
When your archers have mastered basic tuning, they often are curious about more advanced tuning. Let’s jump to the end of the line to look at the Cadillac, no the Rolls-Royce, of tuning: group tuning.
Preliminaries to Group Tuning
This is something an archer shouldn’t undertake unless they have reached a stage where they are consistently grouping well at all distances they are competing in. Since this process is quite laborious, to attempt it before the preliminaries are in place will be a great waste of time. So, this is not for beginners or even intermediate archers.
What Group Tuning Accomplishes
There is a short list of things that group tuning accomplishes. In the early stages it confirms the quality of the tune at all of the competing distances. Later, it is used to expose very small improvements that can be extracted from an archer’s equipment.
Getting Started—Proportional Group Sizes
If a your or your student’s bow and your arrows are tuned well, then consistent groups should be possible and observed. And because arrows are fairly simple projectiles they should show some consistent behavior, one of which is that the sizes of the groups should be proportional to the distances shot.
For example, if your archer shoots three dozen arrows at 30 meters and the diameter of the group is 20 centimeters. If that process were to be shot at double the distance, 60 meters, the diameter of the group should also double, so the group should be 40 centimeters across/high. At triple the distance, you should get groups three times as large, etc. Of course, this is on a windless day with no other influences upon the archer.
So, other than the archer, why might one not get proportional groups? Two common problems are excessive drag and clearance issues. If the arrows themselves have excessive drag associated with them (often this is attributed to poor fletching but it would have to be really, really poor to be the main cause because the drag associated with the shaft is far, far greater than of the fletches), the excessive drag will slow the arrows rapidly and as their speed is lost, the arrows become less stable and groups expand. If this is the case, the grouping at longer distances will be larger than expected. Clearance issues are issues in which the arrow, as it is leaving the bow, strikes something on its way out. That something can be a fletch or even the arrow itself. The thing it hits can be the riser or the arrow rest. It can even be the string dragging on the archer’s chin as the shot is loosed. These issues cause unstable arrow flight from the beginning, which the fletches can damp out over time. This results in groups at the closer distance being bigger than expected when compared with the sizes of the groups at longer distances.
Testing for Proportional Group Sizes A perfect place to do this is the practice butts of a field range because there are almost always a wide choice of target distances already set up. If you are at a target range, you will have to set up targets at the distances your student will be shooting. You will need three, better four, target distances and it makes things simpler if you choose easy multiples of the smaller distance, e.g. 20, 40, 60, 80 yards/meters or 15, 30, 45, 60 yards/meters. You can do it at any four distances, but then you will have to do some math. It is also easier if you use the same size target face.
The process is to shoot enough arrows to establish a reliable group size (you can disregard obvious mistakes). You can determine the group sizes either from the rings on the target (use decimal scoring) or by wrapping a string around the arrows and measuring the length of the wrapping string (a rough circumference of the group). Obviously if you don’t have many arrows, you will need to shoot a number of ends and the string technique is a bit messy (if you have four groups of six arrows, you will have four circumferences and you can just average those). The circumference or diameter (width/height) of round groups are direct measures of “group size.”
It is best if all of the arrows are shot on the same day so that the same conditions exist as well as the archer being whatever they were on that day (no day-to-day variations in mood or physical ability).
Making the Comparisons If you were able to pick four easy distances (20, 40, 60, 80 yards or meters) then the groups sizes should line up as well. The smallest one should be able to be multiplied by 2X, 3X, and 4X to get the other three (or close enough). Do not expect these to be exact. The 40 group size might be exactly half of the 80 with the 60 exactly half way in between, but the 20 group size is off. If so, this means that either the test was a bit iffy (you can just repeat that distance to confirm the number) or you may have a clearance problem.
You may have to do this a number of times to get a set of group sizes you feel good about and are “believable” as to what they are telling you. But when you have done this, you will feel that you have a good idea of what your expected group sizes are at those distances (you will know what is “normal” for you).
And That Was the Easy Part
The basic group testing is to make sure that there aren’t any glaring problems with your setup or tune. Once that is done we can get into fine tuning.
To fine tune your bow-arrow system by group testing, the procedure is the same for nocking point height adjustments and centershot adjustments, even button pressure adjustments. You establish a repeatable group size at one of the longer distances in your “suite.” Then you make a minute change in one of the variables, for example, a 1/32ʺ (0.5 mm) change in nocking point position, and then you check the group size again. Another little change, another test, and so on. You are looking for the group size to shrink when it hits a sweet spot. Obviously you need to test changes both up and down in the nocking point, testing each change. After, say, making four 1/32ʺ downward changes in your nocking point, you need to go back to normal and try making upward changes. Ideally we would see the group sizes shrink and then go back up in size around the “sweet spot.” But we don’t know exactly where we are in that scenario, so we have to feel our way along. And, “ideally” doesn’t come around very often, so we take the best we can get.
Clearly this is laborious and should only be undertaken when your archer has settled form and a settled draw weight and a settled draw length. If your student is still growing, don’t do it. If they are thinking about changing bows, don’t do it.
There Just Has to Be Something Easier!
There are quite a number of intermediate tests that are substantially easier to perform, but are not as fine. We will cover a couple of these next time: Shooting at Vertical and Horizontal Tapes and French or “Walk-Back” Tuning.