Building A Cheap Light Kit For The Chrony

Learning to use the "Shooting Chrony" Chronograph

What Is A Chrony?

The Shooting Chrony is a chronograph that measures the speed of bullets, arrows, shotgun & airgun pellets, paintballs, etc., from 30/fps. to 7000/fps. and with better than 99.5% accuracy.

The Chrony is actually a very simple device consisting primarily of two photo sensors located in each of the black plastic housings at the front and back of the main unit. They are located under the Twin Lenses at the bottom of these housings and they detect the passage of a bullet over them by sensing the change in the amount of light (i.e., the bullet casts a shadow over the photo sensor).

As the bullet passes over the first detector, it trips a counter, which begins to count very rapidly (much as a super-fast stop watch). The counter is shut off by the second photo sensor when the bullet passes over it. The computer in the Chrony then converts this information into either feet per second or meters per second.

The Chrony I have is the very basic F-1 model which measures in feet per second and has just the simple display which shows bullet velocity. Though it is very simple and hard to mess up, I quickly realized that there are three issues that you must pay attention to if you want to get reliable results from this chronograph.

Lighting must be right. Because the Chrony works by sensing the shadow of the bullet passing over the photo sensors, if there are too many light sources (diffusion through trees, etc.), you will either get errors on the display or incorrect readings (usually much lower). The Chrony comes with two plastic diffusers which are designed to be used when there is bright sunlight straight over head which diffuse the light enough to allow the photo sensors to work correctly. If you try to use the Chrony under heavy tree cover, the bullet will produce multiple shadows which will cause inaccurate readings. Proper lighting that produces a single distinct shadow is essential for accurate results.
The bullet must pass over each sensor at the same height. You will get an inaccurate reading if, for example, the bullet passes over the first sensor 4" and 6" over the second sensor. Therefore, you must be careful to "sight the Chrony" to the target and then shoot across the top of the Chrony at that same angle. The manual suggests firing between 4" and 6" above the sensors for best results.
Muzzle blast. If you are too close to the Chrony when shooting a firearm the muzzle blast will interfere with the photo sensors and produce false readings or errors. The manual suggests firearms should be at least 10' away to prevent erroneous readings from muzzle blast.

The area where I shoot is just too shady for the Chrony to work reliably (at all really). My primary purpose in buying the Chrony was to test a couple of loads at the start of a "production run." To accomplish this, the plan was to take a couple of newly loaded rounds out in the woods behind my house and test the velocities using the Chrony. Trouble is, it's all woods back there, no clearing at all. Therefore the Chrony has been useless to me in that environment. That is, until now.

My Home-made Light Kit

For less than $20, I built a light kit that will work in any lighting condition; even in rain. Here are the materials I rounded up for this project:

One string of white Christmas tree lights. (I raided our Christmas ornament box in the attic. Don't tell my wife)
Two sets of cheap 32" mini-blinds.
Four 1/4" dowel rods (with the ends tapered to fit the 3/16" holes on the Chrony to replace the metal rods. This minimizes shock in case you strike one of them while shooting.
Two 1/2" dowel rods used to connect the two light fixtures together for support.
A 4' roll of kitchen drawer liner material to be used as a cover for the light kit. (I found this near where I picked up the mini-blinds)
A scrap piece of fluorescent light fixture lens. These are those plexiglas sheets that you use for fluorescent ceiling lighting. I happened to have a scrap piece I had saved. I used this to cover my light fixture to diffuse the light. I doubt it is really necessary but since I had this stuff I figured I'd use it. I bet it would work equally well without this lens. The lens does offer protection to the bulbs however.
Four small bungee cords to hold the cover down during use.

Construction

After calculating the length the light fixtures needed to be, I ended up drilling 25 holes in the sides of the mini-blind housing and mounting 25 Christmas lights and then covering over all the wiring with another mini-blind housing. This provides a very rugged unit that can withstand some fairly rough treatment. I drilled holes in the ends of the fixtures so the 1/2" dowels can fit in so that it gives the whole light assembly some structure and stability. I added little "sights" to the four vertical rods to make aiming my shots a little easier.

I glued and rolled up a couple of dowel rods on the ends of the roll of kitchen drawer liner material and attached bungee cords so the wind won't blow the cover around when I lay it over the lights.

Here is the light fixture assembly with the support dowel rods in place. Each light fixture houses 25 Christmas lights. Notice the diffusers which I cut from the fluorescent light panels.

I cut the mini-blind upper housing in two pieces and drilled 25 holes to mount the lights in the one and used the other half as a conduit to hide and protect the wiring. Notice the holes on the ends where the vertical rods mount to the Chrony.

The light kit mounted in place. The four little "sights" are exactly 5" above the sensors and provide very easy sighting such that you're firing straight over the sensors and not at an angle. I am very pleased with how well this "sighting" works.

Another view showing the "sighting."

With the "shroud" in place. This should allow the lights to work even if it is a bright sunny day or on a rainy day.

No flash showing the amount of light produced. Seems to work very well.

The biggest limitation with this is, of course, you need an electrical outlet near by. This was no problem for me as where I set it up is not far from an outlet on the back of the house.