Balance: The Weight Behind the Nock

Archery tunes the mass at the front of an arrow in grains and ignores the back of it, because almost nothing is ever added there. A wrap is the exception: a few grams of film on the tube behind the nock, in the place the string pushes. This docket reads what that mass is, where it sits, and what the paper target can honestly say about it.

How much film weighs, and where it sits

The mass is arithmetic, and the register runs it with its inputs named rather than repeating a number without its conditions. On a stated strip of 100 by 25 millimeters, and a stated compound density of 1.3 grams per cubic centimeter, a 2 mil film is about 0.17 grams, or 2.6 grains, and a 4 mil film about twice that. What a mil weighs carries the conversion and the assumptions, and the spec table keeps the rows with their dates.

Position is the other half of the read. The band sits in the cresting area, behind the arrow's balance point, so its lever arm is most of the length of the shaft, and a small mass on a long arm moves the balance more than the same mass at the middle would.

The arithmetic, worked on a stated arrow

On an arrow of 350 grains and 28 inches whose balance point sits 16 inches forward of the nock, a 2 mil wrap in the cresting area moves the balance point rearward by about six hundredths of an inch and lowers the front of center by about two tenths of a percent. The 4 mil wrap doubles both. Added tail weight works the whole case and states plainly what the result is worth: a real direction, a real proportion, and a change below the resolution at which an archer selects front of center.

Spine is a different read and comes out unchanged. Spine is measured by deflecting a shaft with a weight at its middle, so a film on the tube adds nothing to the static figure. The dynamic reading, at launch, is another matter, and the comparison the register reaches for is the lighted nock: mass at the same end, several times heavier, that archers already accommodate by testing.

What the paper can carry

The honest test is a comparison shot in one session: the arrows bare, wrapped, and bare again, the third set being the one that says whether the difference belongs to the film. What the paper can report is where the group moved, whether its shape changed, and whether it repeats; what it cannot report at ordinary distances is a change of a few tenths of a percent read against an ordinary shooting error. Flight and groups sets out the order of the test and the variables that have to be held, and names the one that is most often missed: a wrap that sits under the fletching can mean a refletch, and a refletch changes flight more than the film does.

What this docket refuses to say

It refuses a verdict. Whether a wrap changes an arrow's flight enough to matter is a question the paper answers for one arrow, one bow and one archer, and the register describes the test rather than predicting the result. The arithmetic says how big the change can be; the shooting says whether it arrived; and the desk, which holds no film and no bow, publishes the first and the method for the second, which is what editorial standards allow it to publish.