Check your strings for loose strands and ensure that the centre servings are in good condition. Occasionally re-wax the exposed strands. Ideally a centre serving should be replaced just before it starts to show evidence of wear. What constitutes wear depends on the bow you are shooting, its geometry, and its performance.
The serving performs a number of tasks. It protects the string material, provides a consistent surface for release from the trigger mechanism, reduces friction on the track, and protects the loaders fingers from potential damage by covering possible pressure points on strands of string material.
A breakage of the serving is dangerous. It can result in string breakage and will throw bolts off course. For any bow, if there is a fluffy mess in the centre then it’s too late. Inspection of the serving before, during, and after shooting is essential. Practice will tell the tale on when to change a serving.
Do not use “soft twist” for the centre serving. It is just that – soft. It will not wear well and will stretch allowing gaps to appear and the serving to move. You should use a “fastflite” style serving, and it needs to be put on tight.
Some shooters prefer to use monofilament nylon flatline, which maintains good circularity, for the centre serving. This is quite good, but when it fails it does so catastrophically.
The serving should be literally in the centre of the string, and it must be waxed. Paraffin (candle or drylube stick) wax is best. It is not advisable to use Bee’s wax. It’s sticky and will collect dirt, and then lumps will fall off in your trigger.
The better the performance of the bow the more important the state of the string becomes. Minor levels of wear that may not visible will affect bow performance. If your shots start to go astray it could be down to the condition of the centre serving.
In general terms the higher the performance the bow the more frequently the serving should be changed.
My wife shoots an Ausbow Contender Target Crossbow. Our experience is that a serving, I use Diamondback 0.018, is good for a TC900 – 90 shots plus 12 sighting shots – and possibly a short training session of 3 dozen. After that there is a noticeable fall off in performance. The only thing I have been able to find on the string are the indents made by the claw. These indents I find by touch, I need good light to see them. If they are too pronounced there is a fall off in consistency. I know of no good reason for this affect, nor can I say with certainty that this is more than an indicator of something else. All I can say definitely is that the serving is good for about 140 shots.
My experience is with Dacron. With other materials the answer will be different.
You can use other string materials such as DYNAFLYTE. However, you need to be aware that in the event of a “dry fire”, the prod is more likely to suffer from irreparable damage.
On the basis of shooting two or three times a week, 60 to 90 shots each time, a dozen strings – shooting each in turn and replacing worn centre servings – are good for 18 months, possibly up to two years. In that time some strings will have been discarded as not performing, or as having loose strands, so not all will see the distance anyway. After that performance can become erratic. You will notice that groups get larger.
Dacron stretches under tension, but is to some extent elastic. It stretches during a shot but recovers when the prod returns to rest. However, after a shooting session the string will be longer. Check your string before you put it on and again when you take it off after shooting. The string will be longer after shooting, but will tend to recover.
Unfortunately, Dacron “dies”. It will eventually lose its elasticity and fail to recover. It has always been known to stretch and to reach a limit beyond which it will not go. Once this happens the string is useless. If left for a few weeks it will recover to some extent, but it will only be useable for a couple of dozen shots, if that. It is therefore essential to have more than one string for your bow.
Don’t use a new un-shot string at a competition.
You should shoot at least 3 dozen with a string and replace the centre serving before you use it for competition. It will take this number of shots to ensure that the strands have settled correctly and make the string consistent in performance.
To cater for the above effects you need several strings. The actual number depends on the life of the centre serving and how frequently you want to have reserving sessions. You may find that 3 or 4 strings are enough. Because I like to have a few weeks between serving sessions I start with a batch of 12.
Some Sport recurve bows now come from the manufacturer with a string fitted to the prod. All the comments above about centre serving apply, but the life of the string will be better. Performance drop off is minimal in the life of the string. You are more likely to dispose of a string because of damage. In all probability these strings are made of BCY “X”, but it is possible to use BCY 8125.
Whatever the string material you should regularly check the state of the serving on the loops at the end of the string. Some separation is almost inevitable. If the separation becomes too much the string material will bear directly on the prod and may result in abrasion of the strands and failure of the string.
You should go to a competition with one string for each day plus at least two spares, just in case.