Chrono woes

[MovedWest]

Just took my shooting Chrony out for the first time today and I ran into some weird reads. Some of my rounds that I knew should be between 1000-1100fps were right on, but others were registering as high as 2000fps. I know this can't be right because a 300gr bullet would knock me over at that velocity.

I also had a problem with some of my faster bullets registering whacky numbers, too. Some of my lighter 1600-1700fps rounds were registering ~300fps on the first shot. This all lead me to believe there was something wrong with the way I was doing it.

Just some things I noted about my setup: I was running my test rounds at an outdoor range. It was a sunny day without a cloud in the sky, temp was about 90 degrees. The bench was covered and the shadow was cast over the chrono. I had my white plastic diffusers on due to there being no clouds. The chronograph was set up on a very sturdy tripod about 5-6 feet in front of my bench.

My target was 50yds down range with all rounds accounted for so I'm pretty sure all rounds passed through the guides.

Any suggestions?

-MW

 

[lgjhn]

I've ran into the same thing with mine.
Then one day, I finally had enough of the frustration and decided to put a .223 round thru it to kill it for good.
I then purchased a Competition Electronics model
http://www.midwayusa.com/viewProduct/?productnumber=852429
It's a little more expensive than the Chrony but does not nearly have the frustrating problems that the Chrony had.
You can read the reviews on it at MidwayUSA and see we aren't the only ones that experienced those problems.

 

[Randy1911]

The chronograph was set up on a very sturdy tripod about 5-6 feet in front of my bench.

This is your problem. The chrony was trying to make a reading off the muzzle blast of your gun. It was reading burning powder. You need to be at least 10-12 feet away. If you do this I bet it solves your problem.

 

[NCsmitty]

Randy1911 is spot on in his analysis. 5-6ft will give you weird #'s unless it's a small caliber.
I try to keep my chronograph 15ft downrange to eliminate those errors. Large calibers, be it pistol or rifle, have a lot of muzzle blast as you know.

NCsmitty

 

[The Bushmaster]

Now you know how fast the muzzle blast wave is traveling. Like mentioned in the above posts. Move the chronograph out a few more feet...

 

[USSR]

You need to be at least 10-12 feet away.

+1. Also, the diffusers alone are not enough to keep direct sunlight off the sensors, which will generally result in false readings of hundreds of fps higher. Tape some translucent material between the two diffusers so as to prevent any direct sunlight on the sensors.

Don

 

[TeamRush]

Ditto. I have a cheap crony I use for teaching...
They ALWAYS get put too close to the muzzle by first time users!

I have found that 6' to 10' is usually enough to keep it from registering stupid or seeing 'Particles' instead of the bullet.

Shoot your favorite firearm at night, and have someone see how big the muzzle flash is.
Your crony should be well in front of that distance or it will read the power particle speed instead of the bullet.

 

[MCMXI]

My target was 50yds down range with all rounds accounted for so I'm pretty sure all rounds passed through the guides.

To get accurate results, the bullet needs to pass through a fairly narrow "window". I made a black foam card with a vertical slit that's 2" wide and about 6" tall centered over the sensors. The instruction manual for my chronograph states that the bullet should pass between 4" and 6" OVER the sensors. The sensors are 1" wide so that means the bullet needs to pass through a "window" that's 1" wide and 2" high for the best results!! The card also greatly reduces the chances of hitting the metal diffuser rods (now redundant).

Also, the diffusers alone are not enough to keep direct sunlight off the sensors, which will generally result in false readings of hundreds of fps higher. Tape some translucent material between the two diffusers so as to prevent any direct sunlight on the sensors.

I made some aluminum "diffusers" that are 7" deep (front to back) and quite a bit wider than the useless 2" wide ones supplied by the manufacturer. I tried the wooden dowel idea to replace the steel guides but that was a total waste of time so the diffusers and guide "rods" (now 2" wide strips of aluminum sheet) are integral. I also added a circular bubble level to the chronograph as well.