Your bow is tuned. Cam timing is solid. Paper is clean. Bareshaft and fletched are kissing at 20 yards.
You shoot a five-arrow group. Four of them are inside a baseball. One is two inches out. Every time.
It's not you. It's the arrow.
What's happening
Every carbon shaft has a stiff side and a weak side around its circumference. The mandrel seam from manufacturing is the stiffest line on the arrow. When you nock it up and shoot, the shaft flexes around the rest — and if the stiff side is "up" on one arrow and "left" on the next, they paradox differently coming off the rest.
Two arrows. Same spine. Same weight. Same brand. Subtly different flight.
At 20 yards you barely notice. At 60 it's the difference between a fist-size group and a baseball-size group. At 80 it's missing the kill zone.
The fix
Find each arrow's best orientation, mark it, and shoot every arrow with that orientation pointing the same direction. That's it. Twenty minutes with a sharpie and a bareshaft.
Method:
Number every arrow with a silver sharpie on the shaft. 1, 2, 3 through your dozen.
Pull the fletching off one. Or use a dedicated bareshaft. You can't do this with fletched arrows because vanes mask exactly the thing you're trying to measure.
Set up a target with a small aim point at 25 yards. Shoot arrow #1. Note where the bareshaft lands relative to the dot.
If it hits the dot, that orientation is its best. Mark the current cock-vane spot. Move on.
If it misses, rotate the nock 90 degrees. Shoot again. Repeat: 0, 90, 180, 270. One of those four will hit closest to the dot. That's your indexed position. Mark it.
Do every arrow.
The lock-in
Once each arrow has its indexed orientation marked, move the sharpie number off the shaft and onto the cock vane. Now that arrow always nocks up with its stiff side in the same place.
If you're re-fletching, set your jig so the cock vane lands at the indexed spot. The other vanes follow at 120 or 72 as normal.
If you're keeping the existing fletching, just rotate the arrow in your quiver so the cock vane is always at the same clock position when you nock up. "Cock vane out," usually.
Who needs this and who doesn't
Hunters past 40 yards: yes.
Anyone shooting broadheads at distance: yes.
Target archers: usually already doing it, or shooting factory-indexed arrows like the Easton X10 Pro Match Grade that come pre-aligned.
Brand-new shafts with less than ~50 arrows through them: don't bother. Carbon settles in the first 50-100 shots. Index too early and you do it again.
Bow that's fundamentally out of tune: fix the bow first. Nock tuning won't save a bow with a bad rest position or off cam timing.
Why this is the move
Most archers chase their tail by replacing components or re-tuning the bow when the real problem is arrow-to-arrow inconsistency. The bow is fine. The form is fine. The arrows are all leaving the bow with slightly different launch dynamics because nothing's indexed.
Twenty minutes. A sharpie. A bareshaft.
The Tune wizard in The Forge has a Nock Tuning step that tracks results per arrow if you want to log the work. Either way, you should be doing it.