The Arrow and the Broadhead Are One System

Fletchwise guides are independent and hype-free – we are not sponsored by any archery brand.

Almost every other decision in archery is reversible. Wrong sight, sell it. Wrong release, try another. Wrong rest, unbolt it. Arrow length is the exception – once a shaft is cut, the only direction left is shorter, and there is a hard floor below which you must stop.

That would not matter much if arrow length were independent of everything else. It is not. Three things push dynamic spine around, and they push against each other:

• Longer shaft = acts weaker. More unsupported length flexes more.
• Heavier point = acts weaker. Roughly one spine group per 25 grains of point weight added. Going from a 100-grain field point to a 125-grain broadhead is not a detail – it is a spine change.
• More draw weight = the shaft acts weaker relative to the force being applied.

And here is the part the spine chart does not say out loud: almost every published chart assumes a 100-grain point. If you build to that chart, cut to length, and then screw on the 125 or 150-grain broadhead you actually intend to hunt with, you have quietly moved a spine group weaker after the irreversible step.

You can fix a too-weak arrow by cutting it shorter. You cannot fix a too-stiff arrow by making it longer. So the order is not optional:

1. Choose the broadhead weight first – 100, 125 or 150 grains. This is a hunting decision, not an arrow decision, and it belongs before the saw. The broadhead guide covers how energy and regulations narrow that choice.
2. Run the spine chart with that point weight, not the default.
3. Buy shafts full length and cut in stages – a quarter inch at a time, shooting between cuts. An arrow saw or a proper arrow cutter makes staged cutting practical; a pipe cutter does not, because carbon has to be ground through rather than pinched.
4. Stop at the safety floor. At full draw the arrow must still extend past the rest – about an inch of shaft beyond it is the usual working minimum. An arrow that can come back off the rest at full draw is how people put a broadhead through their bow hand. This floor is not negotiable, and it is what caps how much you can cut your way out of a spine problem.

If you are having someone else cut your shafts, tell them the broadhead weight you are going to hunt with. Most shops cut for a 100-grain point unless told otherwise.

Total finished arrow weight – shaft, insert, point, fletching, nock, wrap, everything – must not drop below 5 grains for every pound of draw weight. This is not a preference, it is the number bow manufacturers publish as their minimum, and shooting under it is treated much like a dry fire: it can damage limbs and cams, and it typically voids the warranty.

Almost nobody breaks this by accident with a hunting arrow. It gets broken by people chasing speed with an ultralight shaft and a 75-grain point on a heavy bow.

Minimum column is the manufacturer floor, not a target. Most hunting builds sit comfortably above it – if yours does not, that is the finding.

Two arrows can weigh exactly the same and fly completely differently, because front-of-center – the share of the arrow’s weight carried ahead of its physical middle – decides how well the front end leads. More forward weight steadies a broadhead in flight and drives penetration; it also drops the trajectory, so ranging errors punish you harder.

The AMO calculation, which you can do on a kitchen table with a tape and a pencil:

1. Measure L – the arrow from the throat of the nock to the back of the insert.
2. Balance the finished arrow (point, insert, fletching and all) on a pencil edge. Measure A from the nock throat to that balance point.
3. FOC% = 100 x (A – L/2) / L

Note the loop: the heavier point you add to raise FOC is the same weight that weakens dynamic spine. FOC is not a free upgrade – it is spent from the same budget.

This is the most common complaint in bowhunting, and the most commonly mis-diagnosed. The instinct is to blame the broadhead and buy a different one. That almost never fixes it.

A field point is a smooth cone. A broadhead has blade area out front, and that area behaves like a wing: it steers the arrow in whatever direction the shaft is already pointing at launch. If your arrow leaves the bow slightly nose-left, the field point mostly ignores it and the fletching cleans it up downrange. The broadhead flies the error and plants the group off to the side.

So a broadhead group that sits apart from your field-point group is not a verdict on the broadhead – it is a readout of a tuning error you already had and could not see. Work through these in order before buying anything:

• Centre shot and nock travel – paper tune or bare-shaft tune first.
• Rest timing and clearance – a drop-away falling late will slap a vane. See the arrow rest guide.
• Spine – go back to the section above with the broadhead’s real weight in the chart.
• Broadhead alignment – spin-test each arrow on a flat surface; a head that wobbles has a bent insert or a crooked ferrule, and no amount of tuning cures it.
• Blade sharpness and rotation – resharpen fixed blades rather than replacing heads, using the sharpening guide.

There is one shortcut that appears to work and is worth naming: switching to mechanicals. They have far less steering surface in flight, so they mask the error and group closer to your field points. That is convenient, and it is why the fix gets recommended so often – but the underlying tuning problem is still there, and it will show up again at longer range or in wind. If you want the honest comparison rather than the marketing one, read fixed vs mechanical broadheads.

Practise with the same heads you hunt with, and practise into something built for it – broadheads destroy bag targets, so use broadhead targets instead.

Every arrow is built from the same four components. The shaft is the body and the single biggest factor in performance. The point – a field point for practice or a broadhead for hunting – threads into an insert at the front. The fletching, three or more vanes or feathers near the back, spins and stabilises the arrow in flight. The nock is the slotted plastic tip that snaps onto the bowstring. The insert is worth naming separately, because it is the cheapest way to change FOC without changing your broadhead weight.

Carbon is the modern standard – light, strong, consistent, and durable. Aluminum is cheaper and very straight but bends more easily, and a bent aluminum shaft is finished. Carbon-aluminum hybrids are premium target and hunting shafts. Wood and bamboo are for traditional bows. For most archers, carbon arrows are the best all-round choice.

Spine is how much the shaft flexes – the most important arrow spec, and confusingly a lower number means a stiffer shaft. It must be matched to your draw weight, your arrow length and your point weight together, using the maker’s chart. The table below is a starting point only, and it assumes a 100-grain point.

Grains-per-inch is the shaft’s own weight per inch, and it is how you steer total arrow weight. Heavier arrows carry more momentum, penetrate better and are quieter; lighter arrows fly flatter and faster. Hunters generally favour weight, target archers favour speed – and everyone stays above the 5 gr/lb floor.

Micro-diameter shafts are marketed hard on wind drift and penetration, and the physics behind the claim is real but smaller than the marketing suggests. Going from a 5mm to a 4mm shaft measures out to roughly a 5% reduction in wind drift – genuine, but your vanes and broadhead profile influence wind drift more than 1-2mm of shaft diameter does. Penetration is similarly oversold: once a broadhead has already cut the hole, the shaft is mostly following that channel through soft tissue, so the diameter advantage that shows up on a foam target is harder to see on an animal. The trade you are actually making is practical, not ballistic – standard-diameter shafts tune more forgivingly and have more insert and component options, while micro-diameter shafts are pickier to tune and often need proprietary inserts. Buy diameter for fit with your rest and components, not for a penetration edge the marketing overstates.

The two families are fixed-blade (blades permanently open – tough, fewer failure points, less forgiving of a poorly tuned bow) and mechanical or expandable (blades closed in flight, opening on impact for a wider cut, at the cost of moving parts and some energy spent deploying them). Which one you can responsibly shoot is partly an energy and regulations question, not a preference – the broadhead guide works through the thresholds, and how to choose a broadhead covers what to look for in the head itself.

Turkey is the exception worth reading separately: the vital zone is roughly softball-sized, so turkey broadheads are chosen for cut width rather than penetration.

• Arrows for a compound bow – matching spine and length to your setup.
• Broadheads explained – fixed vs mechanical and how to choose.
• Fixed vs mechanical – the head-to-head, without the marketing.
• How to sharpen a broadhead – getting fixed blades shaving-sharp again.
• Carbon arrows – why they are the modern standard and how to pick a spine.
• Arrow saws – cut your shafts to the right length cleanly.
• Broadhead targets – what to practise into once the field points come off.

Starting points only, and they assume a mid-range draw length. Longer arrows act weaker too. Always confirm on the shaft maker’s own chart with your real draw length and real point weight before you cut.