How to Sight In a Crossbow

A crossbow is easier to shoot accurately than a compound bow and harder to sight in properly, and the reason is the scope. A crossbow scope has three or four stacked reticles that are supposed to correspond to 20, 30, 40 and 50 yards. Most hunters zero the top one, assume the rest are correct, and find out at 40 yards on a live deer that they are not.

Doing this properly takes about twenty bolts and an afternoon. Here is the full sequence.

Before you shoot anything

Three safety items, none of which is optional:

• Never dry fire. Releasing a crossbow with no bolt on the rail sends every bit of stored energy into the limbs and string rather than into a bolt. It can destroy the bow and injure you. If it happens, stop and have the crossbow inspected before shooting again.
• Use a crossbow-rated target.Crossbow bolts arrive with far more energy than a compound’s arrow and will pass straight through a target rated for vertical bows. Behind the target you need a genuine backstop.
• Shoot only the bolts the maker specifies.Bolt weight and length are safety specifications, not suggestions. A bolt lighter than the maker’s minimum behaves like a partial dry fire.

Then inspect: string and cables for fraying or serving separation, the rail for burrs, and every bolt for cracks or a bent shaft. Wax the string. Discard any bolt you are unsure about — a bolt that fails on release is a serious injury.

Step 1: cock it the same way, every time

This is the step that most quietly ruins accuracy, and almost nobody talks about it. If your rope cocker is off-center by even a small amount, the string is not drawn evenly, and your bolt leaves the rail with a lateral push. That shows up as a horizontal stringing of your group that you will chase with the windage turret and never fix.

Use the cocking device that came with the bow. Center it deliberately on the string. Pull evenly with both hands. And crucially: the method you sight in with must be the method you hunt with. If you sight in with a crank and hunt with a rope, your zero has changed.

Step 2: the 20-yard zero on the top reticle

Set up at 20 yards with the crossbow on a solid rest — sandbags, a shooting bag, a rail rest. You are removing yourself from the equation as much as possible at this stage.

Shoot three bolts at a marked aiming point using the topmost reticle. Aim at the same spot every time; do not aim at where your last bolt hit. Then measure from the center of the group to the aiming point, vertically and horizontally.

Read the click value off the scope turret caps — crossbow scopes vary and the cap tells you what one click does at 20 yards. Adjust once, then shoot another three-bolt group to confirm. Adjusting after every single bolt is how a twenty-bolt job becomes a hundred-bolt job with no zero at the end.

Once you are grouping well, use separate aiming points for each bolt. Crossbows at 20 yards are accurate enough to hit your own bolts, and a bolt with a cracked shaft has to be thrown away.

Step 3: the speed dial, and why it is only a starting point

Most crossbow scopes have a speed dial that rotates the reticle spacing to match your bolt velocity. Set it to your crossbow’s speed.

Here is the trap. The advertised speed on the box is measured with the lightest bolt the manufacturer rates, under ideal conditions, with a new string. Your bolts are probably heavier, your string has some shots on it, and your bow is an individual. Your actual speed is very likely lower than the number on the box — which means the reticle spacing the dial gives you is optimistic.

Set the dial as a starting estimate. Then verify.

Step 4: verify every single reticle

Move to 30 yards and shoot three bolts using the second reticle. Then 40 yards on the third. Then 50 on the fourth if your scope has one and you intend to shoot that far.

Note where each one actually hits. You are not adjusting the scope here — that would break your 20-yard zero — you are recording the truth. It is entirely normal for the second reticle to be dead on at 32 yards rather than 30, or for the fourth to hit low at 50. Write those real distances on a strip of tape on the stock. A crossbow with three honestly labeled reticles is far deadlier than one with four reticles the hunter assumes are correct.

If the reticles are badly off, try a different speed-dial setting and re-verify. If they are close, tape the real numbers to the stock and hunt with them.

Step 5: the broadhead check nobody does

Field points and broadheads do not necessarily hit together, and finding that out on a deer is the worst possible time. Shoot the broadheads you will actually hunt with, in the same grain weight as your field points, at your longest realistic hunting distance.

If the broadhead group is tight but offset from the field points, adjust the scope to the broadheads. You hunt with broadheads; field points are practice. If the broadhead group is scattered rather than offset, you have a real problem — usually inconsistent cocking, a dirty or worn rail, bolts varying in weight, or heads not rated for crossbow speed. Fix the cause before you hunt. Our broadhead roundup covers which heads are built for crossbow velocities and why it matters.

Last thing: hunt with unshot heads. A head you have driven into a target has a dulled edge and possibly a tweaked blade. Keep one practice head for this check and hunt with fresh ones.

Step 6: shoot from your hunting position

Everything above happens from a bench. None of your hunting will. Once you have a verified zero, shoot from the positions you actually use: seated in a chair, from a stand at a downward angle, with the rail resting on a blind window frame.

Two things to check specifically. First, the limbs need clearance — a crossbow limb that contacts a blind window or a stand rail on release is a destroyed bow and a possible injury. Second, downhill shots from elevation hit high, because the effective horizontal distance is shorter than the line-of-sight distance. A rangefinder with angle compensation solves that for a modest price and is the single best accessory purchase for a treestand crossbow hunter.

How often to re-check

Before every season without exception. After any hard transport or a knock to the scope. And always after replacing strings or cables, because new strings change bolt speed, and changed bolt speed changes every reticle below the top one. Three bolts, ten minutes, once a year. It is the cheapest insurance in archery.