You sighted in at 30 yards with field points all summer. Five-arrow groups inside two inches. You're ready.
Opening week, you swap to broadheads. Suddenly you're hitting 4 inches low and right at the same distance. Your buddy says paper-tune. The guy at the shop says try a different head. The internet says check your spine.
Most of the time it's none of those.
Field points are forgiving. They're round and short and they let bad arrow flight hide. A broadhead is a sail. Anything wrong with how your arrow leaves the bow — and there's almost always something — gets amplified the second you bolt on a 1.25" cut head.
What's actually happening is your bow isn't tuned. Not "ok-tuned" the way most pro shops send you out the door. Actually tuned. Cam is a hair off-sync. Your nock is rotated to whatever angle it ended up in when you pulled the fletched arrow out of the press. Your rest is centered against where the riser THINKS is centered, not where your shaft actually exits.
Field points cover all of it. Broadheads expose it.
The order that actually fixes it
Cam timing first. Not paper. Cam timing. If your timing is off, every other adjustment chases something that keeps moving. Get a draw board on it. Both cams should hit the wall at the exact same moment. If you don't have a draw board, find a shop that does. Don't sit around waiting on this one.
Then walk-back the rest. "Per manufacturer spec" is a starting line, not a finishing one. Walk-back until your 20 and your 60 land in the same vertical line. Most modern flagships need the rest moved 1/64 to 1/16 from spec to get there.
Then nock-tune. Every shaft has a stiff side. You want every arrow leaving the bow with the stiff side in the same place. Twenty minutes with a sharpie and a bareshaft. Best single thing you can do for broadhead consistency at distance, and almost nobody does it.
Paper goes last, not first. Paper tells you what's left after you've fixed the upstream stuff. Tail-left tear, spine probably off OR rest is right of center. Tail-high, nocking point. You're not paper-tuning to "fix" the bow — you're verifying you fixed everything upstream.
Then shoot broadheads alongside field points at 30. If they hit together, you're done. If they don't, the broadhead is telling you exactly what's still wrong and which direction.
The part nobody says out loud
A lot of "shop tunes" are paper-tunes with the rest moved until the hole is clean. That's a single-distance band-aid. It doesn't survive distance because everything upstream is still wrong. Cam isn't synced. Tiller isn't checked. Nocks weren't indexed. Bow paper-tunes great. Walks-back ugly.
I run the full 11-step tune on every bow that comes through. About 90 minutes if nothing weird shows up. If you're doing it yourself for the first time, give yourself an afternoon. The Tune wizard in The Forge walks through it in order and remembers where you stopped if you have to come back the next day.
One more thing that bites people: if you switched broadhead weight from your field point weight, you changed your dynamic spine. 100gr to 125gr is roughly 31 spine units softer on a 28" arrow. Enough on its own to take you from "tuned" to "tail-right." Match the weights for tuning, OR run the math in the Spine Calculator tab so you know what you're walking into before you start chasing rest adjustments that aren't going to fix the real problem.
Don't buy a new broadhead. Don't blame the spine without checking. Tune the bow first. Most of the time, that's the whole story.