Glossary of Terms for Archery

This post is intended to be an ongoing project (and is very far from complete at the moment!): a glossary of common archery terms with basic explanations.  If there are any terms you think should be added, let me know.

Parts of the Bow

Back:  the face of the bow that points away from the archer.  

Belly:  the face of the bow that points towards the archer.

Handle/grip: the part of the bow that is held by the hand.

Limb:  the section of the bow that is not the handle.  May consist of bending and non-bending parts.

Nock:  the point on the bow where the string attaches.  May consist of grooves cut into the side of the bow (usually both sides symmetrically but on some historical bows just one side); a groove in the back of the bow (usually on a static recurve) or a protrusion from the tip for the string to fit over, with shoulders to stop the string sliding down (this is sometimes known as a pin nock).  Not to be confused with the nock at the end of an arrow, the action of attaching the arrow to the string or the nocking point on the string.

Rest:  similar to a shelf but consisting of a piece of wood, leather, metal or some other material protruding from (and usually stuck to rather than made from the same piece as) the bow.

Shelf:  a section of the bow, often the bottom of a window, that provides a stable base for the arrow to rest on.

Siyah:  the stiffened tip of a static recurve.  Also known as the ear.

Window/cutout:  a section of the bow at the top of the handle that has been removed.  This serves two major purposes: it makes the bow more centreshot and it provides a shelf.

 

Strings – Parts and Manufacture

Loops:  the loops at the end of the string, that fit over the end of the bow.

Nocking Point:  the point on the string where the arrow attaches.  It is important to get this position right, for optimum arrow flight and to reduce the risk of the feathers’ cutting the hand.  Nocking point also refers to a marker attached to the string to mark this point.  They often consist of small brass “U” shaped pieces that are clamped around the string but it is better to use a piece of dental floss or similar wrapping (since this is lighter and therefore allows faster string movement, as well as not cutting the drawing fingers as brass can do.

Serving:  any of various types of thread wrapped around the string.  Centre serving is the section of thread wrapped around that part of the string where the arrow will attach.  It allows the string to be built up to a thickness appropriate to the arrow without needing to have the whole string that thick (and therefore heavy and slow).  It also protects the string from friction from the arrow.  End serving, also known as loop serving is the thread wrapped around the loops.  It protects the loops from friction and also ensures that the loops stay closed.

 

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Arrow Speed – Graphic Predictions

In my last post I wrote about the testing of my various arrow through my shiny new chronograph.  Since then I have bought two different types of all carbon shaft to try: Easton Apollo 560 and Easton PowerFlight 500.  For the PowerFlights I have a choice of points: 60gn or 100gn points (the Apollos have 100gn points).  Is it possible to predict the speed of these arrows?  Since I have had a flare-up of an old back injury and for the last 48 hours haven’t been able to stand upright or walk without a limp (and ideally a stick) I am going to attempt to do exactly that.

The first big caveat is the one pointed out by Steve Ruis in his comment to my last post: correct arrow spine is critical to speed.  In particular, dynamic spine is important.  As regular readers will know, this is the extent to which the arrow bends as it is shot, as opposed to static spine, which is how much it bends when a weight is suspended from it at rest.  These three variants (Apollo, PF with 60gn and PF with 100gn) are going to have different dynamic spines.  The Apollo, as a .560 spine, is weaker in static spine than the .500 PFs (I am going by the marked spine for these purposes).  With their 100gn points they are likely to remain weaker than the PFs.  The PFs have the same static spine (being identical shafts) but the 100gn points make the dynamic spine weaker than the 60gn points do.  This may well have an effect on speed.  I shall be able to correct for this factor to a limited extent by shooting each variant as a bareshaft first (I am also going to do this with the other arrow types I tested in the previous article).  Having shot the Apollo bareshaft already, I can say that they are a touch weak but not too bad.  They are stiffer than most of the aluminium arrows I tested in the last article (though not than the A/C/Cs, which might explain that arrow’s slightly high performance).

Leaving spine hypothetically to one side, what predictions can we make?  Well, the new arrows weigh as follows (+/- 0.5gn):

Apollo: 360gn

PF w/100gn: 350gn

PF w/60gn: 310gn

We would therefore predict that they would all fly faster than even the fastest (and lightest) of the arrows in other test (which weighed 372gn).  We would expect the PowerFlights to be faster still, with the 60gn tips being fastest (subject, as I say, to the effect of spine).

What is the relationship between mass and speed?  Applying our favourite formula, F=ma, we should expect a linear relationship.  That is to say, since a=F/m, where F is a constant (the stored energy in the bow), we should expect speed to rise in inverse proportion to the drop in arrow mass.  Note that this does not mean that if we half arrow mass we double arrow speed.  The mass that is being propelled by the bow includes the mass of the bow’s limbs and the string.  With that clarification in mind, however, we should expect to see a straight line if anybody were to be sad and geeky enough to draw a graph of arrow mass against arrow speed.  Like the one below, for example.

Arrow speed graph

As you can see, the arrows I tested last time form a straight line, subject to some pretty sizable error bars caused by poor shooting form, variations in spine etc.

I have added dotted lines to represent the three new arrow variants that I intend to shoot in the next few days.  The prediction from the graph (apologies for the unclear numbers on the y-axis: it was late when I drew this graph) is that the Apollos will fly at 192fps, the PF with 100gn points will go at just under 195fps and the PFs with 60gn points will be around 204fps.

As you will have gathered from the various caveats (variations in spine; less than perfect consistency in my shooting technique; differing nocks; drawing a graph at midnight in a childrens’ drawing pad etc) mean that this is not exactly perfect science.  I am not, as one should do, isolating one variable.  My prediction, however, is that factors such as spine difference will not affect the speeds to an extent that trumps weight.  I expect to see the order of speeds as predicted and I do not think that the actual speeds will be out by more than about 5fps.

And as soon as my back heals, I shall test it and let you know!

My New Chronograph

I have just bought myself a chronograph.  Specifically, a Chrony F1 with lighting set.  The lights let you use it indoors but I have no intention of so doing.  It’s just that it was on sale and getting it with lights worked out cheaper than getting it without.

For those who don’t know, a chronograph is a device for measuring the speed of an arrow (or bullet, pellet, paintball etc).  It’s basically a long box with a laser at each end that beams upwards.  It starts an internal stopwatch as the front of the arrow goes through the first beam and stops it as it goes through the second beam.  Using the recorded time and the distance between the beams, it works out the speed of the arrow.  This is a brilliantly useful tool: every time you change something – fletchings, brace height, string material, arrow shaft etc – you can shoot before and after through the chrono and see what effect the change has on your arrow speed (and therefore on your trajectory and point of aim: see earlier posts on arrow speed).  I explained all this to Claire, my loving and long-suffering wife.  She replied “you want it because you’re an archery geek and it’s a cool new toy”.  She was, of course, entirely right; but it is also a really useful piece of kit.

image

The chronograph is famous among archers for its disappointments.  We all expect our favourite bow to be whipping arrows out at 200 fps or faster.  Then we get to a chronograph and discover that we are barely touching 180.  Like all good science, it can be a cruel destroyer of our cherished illusions, but one that should lead us to make informed changes to improve our situation.

Today the chrono arrived and I took it down the woods for a play, together with my Border Ghillie Dhu and a variety of arrows to test.  I ended up comparing the following (all made by Easton and listed: type; spine; mass in grains; grains per pound of draw weight (gpp)):
XX75 Platinum Plus; 2016; 431gn; 11.65gpp
XX75 Tribute; 2016; 429gn; 11.59gpp
X7 Eclipse; 2014; 372gn; 10.05gpp
X7 Eclipse; 2114; 390gn; 10.54gpp
A/C/C; 3-39; 384gn; 10.38gpp

Note: I have assumed for these purposes that I was drawing 37lbs.  This is the marked weight of the bow at 28″.  I did not measure the draw weight or my draw length for these purposes, since the aim was to compare arrows rather than necessarily give accurate gpp readings.

Judging purely by arrow mass, therefore, we would expect the Platinum Plus and the Tribute to be of similar speed, with the Tributes maybe a tiny bit faster.  We would then expect the 2114 Eclipse to be faster than those two, with the 2014 faster still.  We would expect the A/C/C to be somewhere between the two sizes of Eclipse.  Sounding a note of caution here, I will say that I had limited numbers of the X7 Eclipses and had a few error readings (basically I missed the beam).  This means that the speeds for the X7s may be less reliable than the others.

There are other variables beside mass.  One is the nocks.  Nocks can be tremendously important to arrow speed.  The nocks on all of these arrows were the same, except for the A/C/C, which has a rather better (and more expensive) nock.  The remainder all used the same nocks.  The situation is complicated a little by the fact that the nocks on the aluminium arrows (i.e. all except the A/C/C) have been splayed and this can mean that they vary slightly in fit.  We shall keep this at the back of our minds while remembering that I shot at least 3 of each type of arrow and then took an average, which should mean that differences in nock splaying cancel each other out.

Air resistance can be a big factor in arrow speed.  It is determined by a variety of factors including thickness or shaft and size/setup of fletchings.  The aluminium shafts all have the same fletching but in any event we would not expect resistance to make a significant difference at the short range here (I was standing about 3ft from the chronograph).

The average speed of the arrows is noted below (in feet per second):
Platinum Plus: 173.53 fps
Tribute: 177.59 fps
2014 Eclipse : 188.16 fps
2114 Eclipse : 182.38 fps
A/C/C: 194.42 fps

As we expected, then, the Tribute marginally outshoot the PP.  Both are outshot by the  Eclipses, with the lighter Eclipse faster than the heavier one.  The anomaly is the A/C/C.  This went faster than expected from the simple masses.  One explanation may be the nocks.  Another can be seen when the raw data is examined.  On one shot I really went for it, nailing the release, pushing the bow hand forward and probably drawing quite a bit further than usual.  The result was an arrow that went at 208 fps!  If you remove that arrow and stick with a fair comparison of regular draws, the A/C/Cs drop to 187.65, which is in the expected range, slightly higher than we might expect, but that’s likely to be the nocks.  This removal of the faster arrow is not some form of special pleading, by the way: it is perfectly sound to remove an anomalous result from a set of statistics.  This result varied from the mean by more than twice what any other arrow did and produced a result at odds with all of the rest of the data.  Keeping it in would be poor science.

The final adjusted results, therefore, are:
XX75 Platinum Plus; 11.65 gpp: 173.53 fps
XX75 Tribute; 11.59 gpp: 177.59 fps
2114 X7 Eclipse; 10.54 gpp: 182.38 fps
4/40 A/C/C; 10.38 gpp: 187.65 fps
2014 X7 Eclipse; 10.05 gpp: 188.16 fps

This is in accordance with our expectations of reduced mass bringing greater speed.  What lessons have I learned?  Well, for starters I shall stop buying Platinum Plus and go back to Tributes as my basic arrow.  I shall also look at investing in another set of X7s.  Quicks Archery very kindly sponsored me and Claire by giving us reduced rates on X7s before Korea last year.  These have gradually vanished into the undergrowth or been bent around trees or target frames and the time has clearly come to replace them!

I do not claim that this is anything approaching a perfect experiment.  There are various things that should be (and will be) addressed.  One is shooting more arrows so as to get a better idea of the average speed.  Another is getting somebody else to shoot it, to try to obviate any unconscious bias (although I did this to some extent by not weighing the arrows until after I had shot).  My draw length is not as consistent as it should be, although this should have evened out between the different arrows.

This is the first in what will be an ongoing series of articles where I get to play with the chronograph.  I shall set out more detailed and scientific findings in future posts, in which I hope to deal not just with the effect of changing other variables such as brace height but also to try a variety of bows and do some kind of comparison (I am intrigued by the number of relatively inexpensive bows out there that advertise speeds over 200 fps without giving a draw length, draw weight, arrow weight etc.  After reading this post, I hope that you will share my cynicism of such claims).

Theory Into Practice – Tuning Your Arrows and Bow

Enough theory, let’s talk about practicalities.  I’m working on the basis that you have your bow and are selecting a new set of arrows.  To do this you will need to go through a process called bareshaft tuning.  I suggest reading the whole of this post before starting.

You will need a selection of arrows of varying spines.  Some shops will do a set of shafts of varying spines for you to try bareshaft tuning your bow.  If you can find such a deal then great.  If not then your best bet may well be to use wooden arrows for tuning, since they are likely to be cheaper than modern materials.  If you are using wood then I recommend screw-fit points.  This is because you will be removing the point and shortening the arrow, which with regular points means cutting the point off and sticking a new one on.  You might get through a lot of points!

Your starting point is a spine selection chart.  There are loads of them online (just google “arrow spine chart”), some for woods and some for carbon/aluminium.  They are fairly self-explanatory: you cross-reference your bow’s draw weight and your arrow length to get a spine value for your arrows.  This is a starting point only.  If offered a choice of bow types, I suggest using “longbow”, but perhaps selecting a draw weight that is slightly higher than your actual draw (5lbs or so).  This will depend on your bow’s performance.  A really fast Saluki will need stiffer arrows than a budget bow from eBay of the same draw weight.

Bareshaft Tuning

As I explained last time, arrows of the wrong spine will not fly straight.  This is why we use fletching.  Fletchings are great.  They stabilise your arrows and can iron out a lot of problems with spine and arrow flight.  They do this by imparting drag to the back of the arrow.  The bigger the fletchings, the quicker and more effectively they will straighten the arrow.  The downside is that by imparting drag they slow the arrow down, with all the problems that I discussed when dealing with arrow speed in an earlier post.  The less well spined the arrows are, the more time the fletchings will spend side-on to the air, which means the more they will slow the arrow down.  Perfectly spined arrows do not need such big fletchings and such fletchings as they do have will not slow the arrow as much as the same fletchings on badly spined arrows.  Bareshaft tuning involves shooting unfletched arrows to see how well the arrow is matched to the bow.

Standing about 20ft (7m) from the target (ideally a soft “bag” style target), shoot an overlength bareshaft into the target.  It is best to do this with two or three arrows to ensure that any results are not the result of poor technique on a particular shot (if you have poor technique on all your shots then that’s a quite different problem!).  Now examine the arrows in the target.  In particular, look at the alignment of nock and point, as seen along the line from where you shot.

Interpretation

The interpretation of the arrows depends on how you are shooting.  I am going to set it out for a right handed archer using a thumb release, i.e. with the arrow on the right of the bow from the archer’s point of view.  The same conclusions will apply to a left handed archer using a Mediterranean release.  For a right handed Mediterranean release or a left handed thumb release you need to reverse whatever I write here.

If the arrow hits the target “nock left”, which means that the nock is significantly to the left of the point, then the spine is too strong – the arrow is not bendy enough.  Bearing in mind that the bareshaft is too long, you will not be able to get it to shoot properly from your bow.  You should discard it and try weaker arrows.

If the arrow hits “nock right” then it is too weak.  This is what we are hoping for because it is too long and, as discussed last time, the dynamic spine will get stronger as the arrow is shortened.

Assuming that you are getting a nock right impact, you should now remove the point and shorten the shaft by ½” or so.  Reattach the point and shoot it again.  The arrow should now be slightly less nock right.  Remove the point and shorten it again.  Then shoot again and so on.  BE CAREFUL NOT TO SHORTEN THE ARROW BEYOND YOUR DRAW LENGTH!

Your arrow spine is right when the bare shaft is hitting dead straight.  If it gets there too soon (i.e. your arrow is still far too long) then the arrow is too stiff.  If it is still nock right when you reach your minimum length then the arrow is too weak.  In either case you either need to get new shafts or you can try to make adjustments to your point weight or brace height.

Brace Height and Point Mass

Ideally you should not make significant changes to these factors, since they will both have other effects.  Relatively minor changes can be useful for fine tuning.

For reasons discussed in previous articles, a lower brace height will put more energy into the shot.  This means that the arrow will bend more.  In other words, a lower brace height effectively weakens the dynamic spine of the arrow.  Now, you probably don’t want to make more than a minor adjustment to the brace height (1/2” is plenty).  This is a matter of fine tuning.

In addition, brace height changes affect other things about the bow.  I once had a student shooting a Grozer biocomposite static recurve.  It twanged loudly and felt like it was shaking your fillings out when you shot it.  I changed the brace height by ¾” and suddenly the bow shot almost silently and with very little handshock.  If you change your brace height as part of bareshaft tuning, therefore, you must remain aware of these possible side effects.  It may be better to change the arrows rather than the brace height.

The other piece of fine tuning that you can do is changing the point mass.  A heavier point effectively weakens dynamic spine.  A lighter point strengthens it.  Again, however, changing the arrow mass affects flight.  In particular, raising arrow mass decreases arrow speed, so don’t go overboard.  For normal bows in the range of 30-50lbs you will probably want to shoot 100-150gn points.  Lighter is better than heavier, generally speaking.

Bareshaft and Feathered Together

If you already have some fletched arrows that fly tolerably well then you should include these in your bareshafting.  Just mix them in with the bareshafts and shoot them all the same way at the same point on the target.  The fletched arrows can be taken as a control group: the bareshafts should hit to the left of the fletched arrows if the bareshafts are too weakly spined and to the right if too stiff (again, assuming a right handed thumb shooter or left handed Mediterranean shooter).  If you find that this method is giving you different results from the bareshaft angle (e.g. the bareshafts are hitting left of the fletched arrows but are doing so with a “nock left” impact) then the problem is your shooting form and you should be wary of making and adjustments until you are getting consistent results.  If your existing arrows are not spined to the bow then this method is of much less use.

Nocking Point Height

If you nock too high or too low on the string then you will get poor arrow flight and quite possibly cut your hand on the quill of the feather.  Bareshafting can be used to get your nocking point height right.  To set nocking point height properly, you should start with it obviously too high and shoot at the target.  It will impact “nock high”.  Now lower the nocking point by 1/4” or so and repeat the shot.  The arrow should be slightly less nock high.  Repeat this process until the arrow flies straight.

The reason for starting too high is so that you know whether you are high or low.  If you start about where you think it should go then you will not know whether to adjust it up or down.  Contrary to popular theory, a nocking point that is too low will generally give you a nock high impact because the nock end of the arrow is pushed up as it passes over your hand.  If you start too high then all adjustments will be downwards, so long as you only move it a little each time.

That’s It!

If you have read this and my other posts on bow mechanics and arrow dynamics then you will now know all you need to know to set your equipment up properly for maximum efficiency.  Please do take the time to select, tune and care for your equipment.  Even if horsemanship is more important, the archery side of this sport should not be ignored.

As ever, please do post any comments, questions or observations.  I’ve finished with technical stuff for a while.  Now for something completely different…

Arrow Spine: Determining Factors

Now that we have established what spine does, you need to know how to change it. The following factors affect the spine of arrows:

    Shaft Stiffness (Spine)

There are far too many possible jokes for me to bother making any.

Fairly obviously, the most important factor in determining how much an arrow bends is how bendy the arrow shaft is. This will be determined by the material and the thickness of the shaft. The bendiness of the shaft is generally referred to as its spine, but it is important to remember that it is not the whole story. I tend to think of the bendiness of the shaft as “arrow spine” or “static spine”, as opposed to “dynamic spine”, to which we are coming.

Arrow spine is measured in pounds of draw weight but I hope that by now you realise that draw weight is not the only factor. If you have not grasped this point, you might like to read my earlier posts on bow mechanics. Arrow shafts are sold by spine weight, usually in bands of about 5lbs. For wooden shafts you will simply see a box labelled “35-40” or similar. Carbon and aluminium shafts have a slightly odd system of coding, unique to the type of shaft, which tells you the wall thickness, diameter and mass per inch, as well as shaft spine. There are tables, known as spine charts or spine tables that will help you to find the right shaft.

For a given shaft spine, however, you can make the arrow more or less stiff by adjusting the following factors. They all affect how much the arrow flexes when subjected to the force of the bow’s shot. This is sometimes called dynamic spine (i.e. spine when moving).

    Length

Longer arrows are more flexible. Take a long stick and waggle it. Then snap off a 6″ section and try to waggle that. See?

In addition, a longer arrow should denote a longer draw length (you should not have a large amount of arrow sticking out in front of the bow at full draw) and longer draw length means more stored energy and, all else being equal, more force on the arrow, resulting in more bend.

Having said that you should not have a lot of arrow sticking forward, there is nothing wrong with a couple of inches. Leaving the arrows a bit long may therefore be used to lower the spine of the arrow.

    Point Mass

Heavier points make at arrows bend more. When the bow first applies force to the back of the arrow it will bend the shaft until enough force travels up to the point to move the point which, being heavier, needs more force to move. The heavier the point, the harder it is to move and so the more the shaft bends before it moves the point. Put another way, take a stick and waggle it, then attach a weight to the end and waggle again. See?

    Brace Height

Lower brace heights increase the length of the power stroke, thereby increasing the amount of energy available for pushing the arrow. This makes it bend more. Take that stick again and waggle it. Now waggle it harder. See? The same applies to string mass: it changes the force applied to the arrow.

    Overall Adjustment

It is possible, by means of changing length and point mass and brace height, to change the dynamic spine of an arrow quite considerably. Don’t.

Changing your point mass or arrow length affects arrow mass as well as spine. Point mass will also affect something called FOC, which is the proportion of arrow mass that is in front of the middle of the shaft’s length. This affects flight characteristics. Changing your brace height will change the energy available to the arrow and can produce handshock, poor arrow flight and so on.

What you should do is brace your bow at the correct height as recommended by the bowyer, then select the correct arrow spine. Get your arrows about 4″ too long. This gives you a decent starting point for bareshaft tuning, which is what we shall cover next time. Point weight, arrow length, brace height and string mass should be thought of as things you have to keep constant in order to maintain consistent spine once you have found it. In selecting and tuning your arrows in the first place, they are for fine adjustments, not major changes.

Arrow Spine and the Archer’s Paradox

We have come at last to arrow spine and the archer’s paradox. Let us examine the paradox first.

    The Archer’s Paradox

This is a much misunderstood phrase. The “paradox” is that if an archer wants to hit a target then the one thing he should not do is line up the arrow with the target. This was noted in the days before centreshot bows and mechanical releases, which minimise the archer’s paradox. As usual, I shall ignore such matters and assume a regular horsebow.

It is easiest, while I explain the paradox, if you imagine holding a bow vertically with an arrow nocked (or even get your bow out and try it). If you hold your bow so that the string and the handle line up with the target then before you draw the bow back the arrow sticks out to one side. It cannot point at the target because the handle is in the way. When you draw the bow this effect becomes less marked, simply because the nock is moving further from the handle and the point is moving closer to it. The angle is still there, however. If the string is released and returns to brace height then a perfectly rigid arrow would not be propelled directly towards the target.

    Spine

The reason we can hit the target is that arrows are not perfectly rigid. They flex when force is applied. They actually flex quite a lot. If you get the chance, I recommend looking on YouTube for high speed footage of the archer’s paradox. Beiter have some excellent clips.

The fine detail is not terribly important, but basically what happens is that as you release, the string does not go in a straight line to brace height. It rolls off the tip of your fingers/thumb, which has the effect of moving the arrow’s nock end laterally away from the bow (this is easy to visualise if you think about the release). The string is also moving forwards and the effect is to bend the arrow and propel it forwards. The string is now moving on slight angle because it is returning to brace but has been moved to the side on release. This, together with the fact that arrows don’t like being bent, causes the arrow to flex back the other way as it is driven forwards. On release it will continue to flex as it flies, although various factors will help it to straighten out more quickly, notably drag at the nock end caused by the fletchings.

This is where the magic of spine becomes really useful: if we select our arrows to bend exactly the right amount on release then it will bend around the bow’s handle and fly directly at the target.

The next couple of articles will be about spine. The first will deal with the factors that affect spine and the one after it will be on how to test and adjust spine.

One important point before I move on to those topics, however, is that the most important thing is that all your arrows should match. They should be of the same mass and the same spine. That way at least you can shoot one and know where the others will go. If your arrows are of different mass and spine then you cannot know where to aim because you cannot know how each arrow will act. It is better to have all your arrows slightly wrong than some right and some wrong. How close they have to be to each other is a matter of personal tolerance. Personally, I ensure that all of my arrows are within 5gn of each other in mass and within 5lbs of each other in spine.

Next time, we shall look at the various factors that impact on the spine of an arrow.

Bow Mechanics 3: String Theory

Yes, I know I said that the next post would be about arrows but you shouldn’t believe everything you read online.  I want to deal briefly with strings before moving on to arrows.

First and most importantly, you must check with your bowyer before you change your string.  Use of an unsuitable string can break your bow beyond repair.  Be warned!

There are many different kinds of string.  In particular, there are various string materials and two main ways of turning the threads into a bow string.  I am not going to go into much depth but I want to discuss two main features of strings that can affect performance: stretch and mass.

String Stretch

You might think that a nice elastic (stretchy) string would give some extra pace to the arrow.  You’d be wrong.  If you use an elastic string then at the end of the power stroke it doesn’t stop dead, leaving the arrow to fly off.  Instead, the string slows down as it stretches.  By the time the arrow flies off it has lost some of its speed.

Studies in fact show that the various modern materials are unlikely to differ enough in their stretch to make a significant difference to arrow speed.  Materials such as B50, Dacron, FastFlight etc have different elasticity but they are close enough that the difference in arrow speed from stretch will be no more than 1 or 2 feet per second (fps).  This is about the same as increasing your draw weight by 1 or 2 pounds.

The way the string is put together will also affect stretch.  There are two basic methods of making a string: Flemish splice (also known as laid in) and endless loop.  You don’t need to know the technical differences but it is worth knowing which you have.  As a general rule, Flemish splice strings have slightly more stretch to them.  Endless loops have higher performance: they don’t stretch as much and they can be made identical more easily than Flemish strings (allowing you to maintain performance the same with spare strings).  The Flemish splice string will also “creep” more.  This means that once the bow is braced the string will stretch so that it becomes slightly longer.  This, of course, lowers your brace height over time, making consistency harder to achieve.

So why would anyone choose a more elastic string than necessary?  Because they are more forgiving on the bow.  At the moment that the string snaps taut there is an awful lot of force going through the tips of the limbs where the string attaches.  If there is no ‘give’ in the string then weaker tips will break at this point.  This is the main reason why you should check with your bowyer before using a new type of string.  In particular, bows made from traditional materials such as horn, wood and sinew may well not be able to cope with modern low-stretch strings.

String Mass

String mass generally has a greater impact on performance than stretch.  A high-performance string material such as FastFlight or Dyneema weighs much less than something like Dacron (which is what most “off-the-shelf” strings are made of).  To take an example, I have in front of me two strings.  One is a Dacron string that weighs (including the serving) 151gn.  The other is FastFlight and weighs 63gn.

So what?  Well, the string, like the arrow, is a mass that needs to be driven forwards by the bow’s stored energy.  The heavier the string, the slower the arrow will be.  According the Traditional Bowyer’s Bible, Vol.1 (which admittedly deals primarily with straight limbed wooden bows), a 20gn increase in string mass will slow the arrow by roughly 1fps for a bow of around 50lbs draw weight.  The effect is greater on lighter bows (because a greater percentage of the stored energy is needed to move the string).

This assumes that the added string mass is evenly spread.  Mass added to the centre of the string has about 3 times the effect (as does mass added to the arrow, but we’ll come to that in a later post).  Those little brass nocking points clamped to your string weigh 5gn each.  If you have two of them on your string and are shooting a relatively light bow then you could be losing about 2fps just from them.

All this may not seem very much but there are good reasons to get it right.  One is that the string is the cheapest way to gain arrow speed.  Bows and arrows are expensive but a decent string is not.  If you can reduce your string mass by 100gn (which you could easily do if your current string is one of the big heavy horrors that you sometimes find) and replace your brass nocking points with a dental floss wrap or similar then you can make considerable gains in arrow speed.  Further gains can be made with your arrows, to which I shall turn next.