One of the very best aiming techniques when eschewing sights is stringwalking. Basically, stringwalking is just hooking onto the string slightly below the arrow in order to shoot distances inside of your point-on-target distance (using ordinary point-of-aim technique).
So, if your three-finger-under string grip when your tab is touching the bottom of your arrow is, say, 40 m then moving down the string in small increments will allow you to shoot targets inside of 40 m using the same sight picture.
This is in contrast to gap shooting in which you must aim higher or lower than the center of the target on every shot not at the POT distance. In stringwalking, the sight picture is always the same.
Stringwalking works because when you draw and anchor gripping the string below the arrow somewhat, you are just rotating your bow so that the arrow is pointing slightly downward. Doing this de-tunes your bow, of course, so there are limits. As a rough estimate, a crawl past two inches below the arrow is fairly extreme.
The detuning is substantial which is why we “walk” down the string and not up (which is a much worse detune). As an example of the detuning, a recurve bow is usually set with its tiller to be one eighth to one quarter of an inch positive. If you are shooting three-fingers-under, it is more typical to be about 0˝ of tiller. This is difference in string grip has the effect of moving the center of pressure of the string grip down the width of your top finger. A crawl of 2˝ would be 2-3 times as much as that change in the string center of pressure, so tiller is going to be way off at that crawl. (What archery giveth with one hand, it taketh away . . .)
The Point of this Post
The message I want to give to you in this post is that you need to be very precise in setting your crawls. One would hope you would be accurate, too, but here I am talking about being precise.
Here is a series of photos showing me making a crawl. The first photo shows the initial placement of the my tap so that it is touching the arrow and the base of the tab is up against the string itself. This allows me to make sure the tab is in the same position each time.
I use the stitches on the tab to gauge how much of a crawl I am setting up but recent rule changes allow printed scales now (very limited printed scales). Once I have decided how much crawl I am taking, I then insert my thumb nail into the center serving in that location.
And this is where you need to be very careful. I have the bow, bowstring, and my head in the same position each time and I sight along the top of my thumbnail when I am setting that crawl distance. (“Be wery, wery careful . . . he, he, heh.” Elmer Fudd He may be a cartoon careful but that doesn’t make him wrong.)
Then the tab is slid down to the spot my fingernail is at and again, I am sighting along the top of my fingernail to make sure everything is consistently lined up.
From this point onward I have a 2-3˝ draw on the bow to keep my hands from slipping out of position (because if they do, it is “do over” time). You need to be ready to shoot as soon as your crawl is set.
I set my crawls down to the quarter of the length of a single stitch, which is less than a sixteenth of an inch/1 mm. That amount of crawl equates to just under two yards of distance on one of my bows . . . which is why you need to be precise. Consider how carefully sight shooters set their sight apertures. I ended up converting many of my “ten click sights,” sights whose “micro adjustment” made ten clicks per rotation (and a whole rotation wasn’t that much) when I discovered that at 90 meters by groups were centered on the nine-ring above the ten and one click adjustment cause my groups to be centered on the nine-ring below the ten. Those sights are now “twenty click sights.” (Actually the groups were 10-9-ish and I couldn’t get them to center on the ten ring. Gosh, I wish I could shoot that well again . . . truthfully, that period lasted only a little over a year when I was practicing up a storm.) Setting crawls is not as precise as setting a good sight aperture, so if you are at all sloppy, you are throwing away a fair amount of precision.
Addendum I mentioned “walking up the string” in passing, dismissing it somewhat but it isn’t entirely illogical. For example, if you have a young sight archer struggling to make distance, one easy fix is to swap his tab for an opposite handed one and have them shoot “two fingers over.” Yes, you read that right. The slot in the tab for the arrow for an “upside down opposite handed tab” is between the second and third fingers then. This grip moves the arrow down the width of the middle finger which is substantial. When I did this I got around an extra 10% cast (28% better when I shot three fingers over). What your archer will get depends.
This is just a stop gap measure your archer can take until he/she grows taller (longer DL) and/or stronger (higher DW) and it only costs about $10 for an off-handed tab. This is only needed for their longest distance and they can go back to their regular tab for all of the shorter ones.