Experimenting with chronograph use for the best results.
First, why do I care about a speed measurement for my bow? I’m not a speed freak although I do try to optimize my set up in order to minimize trajectory and increase hit potential at unknown distances with my short draw length. Another reason is I’ve had good luck establishing correct arrow spine and good broadhead flight by using Archer’s Advantage software for my arrow selection with good broadhead flight being of extreme importance to me. I long ago gave up on the oh-too-generic arrow manufacturer charts for arrow selection.
The individual bow’s set up and its performance will be unique to all other bows and not even near its ATA rating (I promise you). It is unique to what its axle-to-axle, brace height and draw length are set at as well as the string and cable materials, serving materials and do-dads on the string like peeps, nock sets, loops and silencing devices. So, for me, establishing the bow’s performance is critical to finding the best arrow for my set up which will deliver the best broadhead flight.
In a recent session the chrony read 292 fps for the first speed-measured arrow out of a new bow that was rated about 20 fps quicker than the fastest bow I’d ever owned. That seemed pretty good for 68 lbs at my 26.5” draw length and I was pretty happy. The Gold Tip 55/75 arrow weighed 358.2 grains. I rustled up an Easton ACC 3-49 weighing 369.5 grains that I intended to use for the upcoming season. 311 fps – smoking! Problem was there is no possible way a heavier arrow should be 19 fps faster than a lighter arrow. Problem, problem. So, I broke out the previous year’s bow and arrow combination and ran it through the chrony as a bench mark – 248 fps – right on mark.
Obviously something was wrong somewhere. The Competition Electronics ProChrono Digital Chronograph resides in my dark basement so it requires some auxiliary light to work properly. Being too cheap to buy the auxiliary light kit I have two 500 watt work lights I arrange on either side of it and leave its diffusers in place on top. Knowing that the light kits are usually mounted on top I decided to mount one single work light over the top of the chronograph. It is important to note that up until this point I’d not had any reason to doubt the validity of the chrony’s readings and had even verified them against the chrony at my local archery club.
Chronograph in the basement. Note how dark it is even with auxilary lighting.
I dug out my workhorse arrows, the Cabela’s Stalker Extreme 400, and ran one through. An average of five shots for this 376.8 grain arrow produced 283.8 fps. Things were all over the place. So, I replaced the battery and re-ran the same 3 different arrows through the chronograph again with the results reported below.
Speed readings with chronograph in basement utilizing non-OEM auxiliary lighting (3 arrow averages):
- Gold Tip 55/75 weighing 358.2 grains = 292 fps
- Easton ACC 3-49 weighing 369.5 grains = 311 fps
- Cabela’s Stalker Extreme 400 spine weighing 376.8 grains = 283.8 fps
I dug through all my cra…, er stuff, and located the operating manual. It indicated the best results would be obtained by using the chrony outside on a cloudy day. If the day was sunny it recommended using the provided light diffusers. Basically this chronograph works by measuring how quickly the shadow of the projectile passes over two windows in its top. Diffused light, like on a cloudy day, works better for this than direct light. So, it was off to the outdoor range at local West Allis Bowmen where tall bales make it easier to shoot through the chrony outside. The day was sunny so I put on the diffusers.
Speed readings with chronograph outside on a sunny day (3 arrow averages):
- Gold Tip 55/75 weighing 358.2 grains = 275.3 fps
- Easton ACC 3-49 weighing 369.5 grains = 269.3 fps
- Cabela’s Stalker Extreme 400 spine weighing 376.8 grains = 267.0 fps
Those readings were consistent when compared to one another and consistent when compared to their weight. That was good news. I waited patiently, always consulting Mrs. dustyvarmint, the amateur meteorologist, and was finally rewarded with a cloudy day. Back to the range. I once again ran the same set ups through the chrony leaving the diffusers in place with the below results.
Speed readings with chronograph outside on a cloudy day (3 arrow average):
- Gold Tip 55/75 weighing 358.2 grains = 275.0 fps
- Easton ACC 3-49 weighing 369.5 grains = 269.6 fps
- Cabela’s Stalker Extreme 400 spine weighing 376.8 grains = 267.0 fps
The cloudy results were very consistent with the sunny results and had more fidelity overall than the basement results under any lighting condition. While I wasn’t as excited about 269.X fps with those ACC’s as I was about the 311.0 fps I was happy to know the truth and went forward with arrow selection and make up. In this case I’ve had the best accuracy and scores of any rig in a long time.
Chronograph outside on a sunny day with diffusers installed.
So, lessons learned for me. In the future I’ll make sure I take readings outside in reliable light. Selecting an arrow based off the 292 or 311 fps readings would have insured a grossly over-spined arrow and likely would have resulted in tuning problems and poor broadhead flight. I guess if all else fails reading the instruction booklet is advisable.
happy hunting, dv
If you liked this blog you may like the following:
- Packin It In And Out – Treestands
- Overhauling A Hunting Bow
- Archery Release Mystery Solved
- Rangefinder Carry Tip
- Short Draw Bow Speeds And Technical Discussion
- Short Draw Bow Kinetic Energy And Trajectory
- Multimeter – A Handy Bowhunting Tool
Feedback, Questions & Comments
I’d like to hear your tips, feedback, comments or questions. Please leave them below.
Subscribe
Like this blog? Want to be notified of updates? Subscribe via RSS feed by clicking here.
Copyright © Jerry E Long, 2009-2011
