CENTRE SHOT and LAUNCHER CLEARANCE

If you are shooting with a release, your arrow must be aligned so that it is pushed in a perfectly straight line.   For a two-wheeler this means that the string must be aligned, initially at least, with the string groove of the cams.  Please note that this is not the same as aligning it with the centre of the limbs (have a look - the string groove is offset quite a bit to the outside of the limb), and is certainly not the same as aligning it with the centre of the riser, which may or may not be in the same plane as the string.

Finger shooters will need to align the arrow so that it is a little to the outside (left for a right-hander) of the string, when the string is aligned with the grooves.

There are two effective ways of making this alignment: by eye, and by measurement.

Aligning by eye

Place an arrow on the string and on the launcher (if you use a drop-away launcher, either temporarily reverse the spring, or prop the launcher arm up in some way - don't try to align with the launcher down).  Hold the bow at arm's length, and make sure you are looking straight along the string grooves, top and bottom.  Adjust the launcher until the arrow is in exact alignment with the string, or if you are a finger shooter, so that the point appears to be just outside the string.  Use any clues your bow may provide, such as the edge of the arrow shelf, or any casting marks; don't use stabiliser alignment unless you know it is true, which would be quite a rarity!  

You may find this is not quite as easy as it sounds, if so, you might like to use the second method, at least as a double-check...

Measuring across the limb

Measure as precisely as you can from the edge of each limb tip to the near edge of the string groove; don't just assume that the distance will be the same, measure both.  Place adhesive tape across each limb at exactly the same distance from the riser, about half way up each limb, ie where the limbs are the same width.  Make a mark on the tape equal to the tip-to-groove distance you measured previously.  Use these marks to align the string and then align the arrow.

A note on centre shot gauges

At least one manufacturer makes a centre shot gauge, but I can't recommend it.  In the first place, it is unnecessary (but when did that stop a keen archer?).  More important, few risers have a flat area absolutely parallel to the centre line of the bow, so the gauge can give very misleading results.  Incidentally, even the sight block mounting is not parallel on many bows. This is the main reason I recommend you not to change your sight extension from distance to distance - it changes the windage as well.

Launcher Clearance

In general an arrow 'rest' allows the arrow to be supported from the side, as well as underneath - like a conventional recurve rest.  A 'launcher' only supports the arrow underneath.  Finger shooters generally use rests, release shooters use launchers (except the ones that don't, because archers are like that!).

Finger shooters need to adjust their rest and fletchings in exactly the same way as for recurve, ie making sure that the fletchings will pass the riser cleanly and not having too long a rest arm.  Release shooters have a rather different set of problems because there is no sideways movement of the arrow shaft to carry the fletchings clear of the launcher, and the nock is raised very little, if at all - ie there is no 'archer's paradox' and near-zero nocking height.  

Launcher OK - No fletching touch

Launcher too wide

If you are using a conventional launcher, make sure that the support arm is narrow enough to pass between the fletches, or use a 'prong' launcher that allows the fletch to pass though it.  Also make sure the tension in the launcher is the minimum needed to support the weight of the arrow at full draw. 

If you have problems with fletching clearance, you should consider a drop away launcher.  Look in the retailer's catalogues or web sites if you haven't seen them, but they do just what the name says - they drop away as the arrow moves forward so they are 'gone' by the time the fletches pass over them.  Although a keen fan of drop-aways for several years, I have recently revised my thinking.  Drop-aways certainly make fletching touch a thing of the past and make precise nock indexing irrelevant.  However they can be unreliable with fast arrows (they don't fall fast enough) and they give problems in the rain.  On the whole, I would now advise a conventional launcher/rest and only look to a drop-away if there are real problems.  And, incidentally, whether you are looking for a drop-away or a conventional launcher, do not get one that relies on magnets - a little experimentation will soon show you how inconsistent they are - I'm afraid they belong in my 'avoid like the plague' category (sorry Sante).