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Downrange Speed Sight-In Method

This document details the Downrange Speed sight-in method. This method is extremely precise and is not reliant on accurate user-supplied sight marks.

Which chronograph should I choose?

That's a tough call.

The Lab Radar is quicker for this purpose specifically, as it can gather speeds at multiple distances in one shot. It's also quite a bit less expensive than the Garmin Xero.

However, it's bulky, the interface and app is a bit clunky, and it requires an external trigger clamped to your bow to consistently pick up shots in our experience.

Note

Lab Radar has quit making their archery trigger. We now recommend the JKL Gen 2 Trigger. Doppler trigger mode does work, but we have had much more consistent success using an external trigger such as the JKL.

We mount the trigger to a spring clamp with hook and loop fastener.

The Garmin Xero is much smaller and user friendly. However, it does require that you place it downrange to shoot over the top of it. This can be a bit of a pain if going through this process a lot. Not to mention, somewhat risky to fling arrows over the top of your expensive chronograph. We always recommend putting a target or some other kind of 'shield' in front of the chronograph to protect it from errant shots.

BowBars Archery LLC has made some great 'shields' for the Garmin Xero that are available here. These mount to any tripod, are built out of 1/4" steel, and have a QD system for the Garmin Xero. We highly recommend these if you're going to be using the Garmin Xero for this purpose.

Warning

Precision Cut Archery and BowBars Archery LLC are not responsible for any damages caused by using these products or gathering downrange arrow speeds. Proceed at your own risk!

Note

At this time, we are unable to recommend the Athlon Rangecraft chronograph for this use. We have several reports from our customers that their readings are consistently 5-10 fps higher than the Lab Radar and Garmin Xero, and therefore are not producing accurate sight tapes.

Founder Tristan's Thoughts

If I'm going out specifically to make tapes, I almost always grab the Lab Radar. It's just so much quicker and easier than shooting over a Garmin.

If I just need a quick launch speed, or if I'm throwing something in my bag for travel, I'll grab the Garmin. It's much handier and enjoyable to use.

If I was a long range rifle shooter as well, or if I just made a tape every now and then, I think I'd choose the Garmin.

If I'm constantly making sight tapes for new setups, or making sight tapes for other people, I'd choose the Lab Radar.

As far as accuracy goes, both produce exceptional (and identical) sight tapes when used properly.

The Data We Need

Density Altitude

Read more about density altitude here.

Ranges

These are the ranges you will measure arrow speeds at.

With the Lab Radar, we like using 20-65 yard readings.

With the Garmin Xero, we like using 1 and 60 yard readings.

The exact choice of ranges hasn't seemed to make any difference in the tapes produced - even in tapes out to 150+ yards. They're all virtually identical.

We choose these ranges for each unit simply for convenience.

Downrange Speeds

These are simply the speeds of your arrow at the ranges specified above.

Reference Mark (optional)

If you are shooting a 'target sight' that has a built in reference scale / click system, you can choose to enter a reference mark for a distance of your choosing. You can think of this like a 'zero' that we use to calculate marks for other distances. This shot-in reference mark should be at a reasonably far distance to minimize error.

Tips for Gathering Downrange Speed Data

Lab Radar Tips

The Lab Radar makes this process very quick and easy, as it gathers speeds at multiple distances in one shot.

Important Lab Radar Settings

These are the most important settings we use for the Lab Radar. Other settings can be set to your preference, but these are the most important for getting consistent and accurate readings with archery equipment.

  • Trigger Source
    • Trigger - Select this if you are using an external trigger such as the JKL Gen 2. We've had much more consistent success using an external trigger over Doppler trigger source.
    • Doppler - Use this if you are using Lab Radar without an external trigger. Some users have reported success with this, but we've had much more consistent success using an external trigger. It can definitely work in a pinch.
  • Velocity Range: Archery
  • Projectile Offset: This is how far you are to the side of the unit. If you set this to 6 inches, you'll want to position the bow 6 inches from the side of the unit while shooting.
  • Distances: We generally use 20yd and 65yd. 65yd seems to be about the maximum distance that we can consistently get readings at.
  • Arm Time: We prefer to max this out.
  • Screensaver: We prefer to max this out.

Lab Radar Setup

  • We mount the Lab Radar to a tripod.
  • We use an external battery pack (like an Anker battery) to power the Lab Radar. We have not had good luck powering it from AA batteries.
  • We mount the external trigger (JKL Gen 2) to a spring clamp with hook and loop fastener.

Other Lab Radar Tips

  • Ensure the Lab Radar is aligned with the target using the sighting groove on the top of the unit.
  • We'll typically shoot at a 70 yard target when getting readings out to 65 yards.

Note

We have found the Lab Radar to be inconsistent indoors, even in large indoor ranges (likely due to interference). We recommend shooting outdoors in an area without any obstructions between the archer and the target.

Garmin Xero Tips

Gathering downrange speed data with the Garmin Xero is a bit more involved, as it requires you to place it downrange to shoot over the top of it.

Important Garmin Xero Settings

  • Start a new archery session.

  • Projectile weight is optional - use this if you'd like the unit to calculate your KE. It is not required for accurate speed readings.

  • Under Settings > Pro Settings, there is a "Downrange mode" setting you can turn on to enable a visual alert (flashing screen) when a shot is detected. This is helpful to determine if a shot was detected when the unit is placed downrange.

Garmin Xero Setup

  • We mount the Garmin Xero to a tripod.
  • We use a 'shield' to protect the unit from errant shots.
  • The arrow should pass within 5-15 inches of the unit.
  • While gathering velocity readings with the Garmin, leave ~10 yards or so between the unit and the target so the unit has time to detect the arrow.

Tip

For archery equipment, Garmin recommends at least 7 yards between the unit and the target in order for the unit to have time to detect the arrow.

  • Start by getting your bow on target at 70 yards.
  • Gather a 1 yard velocity reading.
    • At this point, you have your "launch speed" for your setup.
    • Use this to add a "Quick Start" sight in for your setup in our application.
    • We'll use this to determine the ideal positioning of the Garmin at 60 yards.
  • Navigate to the Shot Solver feature of the application and run a simulated 70 yard shot. You can then look at the trajectory plot for this shot.
    • This will give you a good idea of where your arrow is at 60 yards when shooting at a 70 yard target.
    • For example, for this setup, we can see the arrow is about 14 inches from the line of sight at 60 yards, while shooting at a 70 yard target.
  • So, to gather our 60 yard reading, we will want to place the Garmin right in our line of sight, if not a bit higher, to put the unit within the recommended 5-15 inches from the arrow.

Note

The Garmin effectively measures the speed at the position of the unit. The ranges should be measured from the shooter to the unit. For example, for a 1 yard reading, you'd want to place the unit 1 yard in front of your shooting position. For a 60 yard reading, you'd want to place the unit 60 yards from your shooting position.

Entering the Data

Here's what it looks like to configure a setup with the Downrange Speed sight-in method:

Validating the Sight-In

Once you've entered your data, the easiest way to validate is to print out a sight tape or mark sheet and shoot it in at the range.

Tip

When putting a fresh tape on your sight, we always recommend 'zeroing' your tape as far as possible.

For example - get your bow hitting perfectly at 60 yards. Then, put the tape on your sight so your indicator points to 60 exactly. Then, you know 60 in reality is 60 on the tape. Then, work your way in and out from there to validate the other ranges.

If you set your tape and indicator at 20 or 30 and then work your way out, there's a high likelihood that there's some error in this closer mark that will show up as you move to father distances.