Let There Be....Not So Much....Light

[BLTsandwedge]

Perhaps it's because I've not looked hard enough, but one point of interest regarding chronograph use that I've not read much about is the very real phenomenon of light refraction from the ground. Seems that I'd been getting poor results from a newly purchased CED Millenium chronograph- and to make a long story short, sunlight reflecting off pea gravel was striking the underside of the passing projectile- negating its shadow and rendering it invisible to the light meters.

Mal Paso, being a head smarter than me and a recovering professional photographer to boot, cured the problem by placing black panels lenghtwise against the skyscreen posts to make more or less a black half-pipe the lenght of the chronograph. The light reflecting from the ground had no chace to shine on the projectile- being blocked by the bottom of the chronograph and the panels. The skyscreens did their job- allowing sunlight to cast a shadow of the projectile over the light meters. Voila. Excellent performance with the chronograph in all respects.

Soooo.....regulating the amount of light your boolit is subject to is certtainly a troubleshooting action to be tried when you get funky readings or no readings at all.

The ongoing question for those of us who have used chrongraphs for aeons- what other pitfalls can we expect- what other troubleshooting opportunities are there if chronograph troubles threaten to ruin an afternoon of data collection?

Thanks and regards.......................Tom

[home in oz]

Who would have thought?

[runfiverun]

light from the side.
direct light from above.
iv'e had to put a shade made from a campaign sign on the top to diffuse light on sunny days.

[HammerMTB]

a shade made from a campaign sign

AHA! At last, something they're good for!
I mean politicians, not campaign signs....
Politicians make campaign signs
It turns out they are not completely useless! [smilie=1:

[shootingbuff]

light from the side.
direct light from above.
iv'e had to put a shade made from a campaign sign on the top to diffuse light on sunny days.

I.ve used a sheet of newspaper on more than one occasion. I guess it could have provided enough of shade to keep from reflecting back from the ground. Any way it has worked for me when I figured the sun was just to dang bright.

sb

[Doc Highwall]

I found this picture where the person used foam board covered with velvet.

[BLTsandwedge]

I found this picture where the person used foam board covered with velvet.

Doc, that be Mal Paso's rig. It works very well.

[luvtn]

That is interesting. I don't have a chronograph, but I thought they worked on electro-magnetic disturbance by the projectile. No one has mentioned a camera.
luvtn

[snuffy]

That is interesting. I don't have a chronograph, but I thought they worked on electro-magnetic disturbance by the projectile. No one has mentioned a camera.
luvtn

That's what ya git fer thinkin!:kidding:

They're electric eyes that react to a reduction in light caused by the shadow of the boolit passing over them. They start and stop a high frequency timer, then the "brain" in the chrono counts the pulses and converts it into FPS.

Light can reflect off the ogive of copper bullets causing the screens to read an increase in light to trigger early. That causes high readings.


The ongoing question for those of us who have used chrongraphs for aeons- what other pitfalls can we expect- what other troubleshooting opportunities are there if chronograph troubles threaten to ruin an afternoon of data collection?

My pact chrono was having troubles when I first tried to test some loads from my 300 WSM. I called pact, he said 3 things I could try. One was to put it further out front, at least 15 feet. Muzzle blast can mess with readings. Second was to make sure the cords were not intertwined/twisted together. They aren't sheilded so they can interfere with each other. Third was to put the box on the bench next to the one I was shooting from. It seems the vibration of the bench can cause some problems. It worked flawlessly after those few tricks.

[lwknight]

BLT , thanks for sharing that info. I had never thought about light from below.

[quack1]

If you want to get some really odd readings, chronograph in bright sun with a layer of snow on the ground. I don't usually chrono in the winter, but last year had a few trial loads I couldn't wait for spring to try, and went to the range when there was about a foot of new snow. Over 4000fps from a 380. All that sunlight reflected off the snow really screwed up the electric eyes of the chrono.

[onesonek]

Good idea,,,,I was having problems too, untill I started parking my j eep sideways and using the rear hatch as an umbrella

[Doc Highwall]

Some times it is not possible to put the main unit on the bench next to you so I place it on a piece of foam with a blast shield.

[Mal Paso]

All the points are important.

Put the sensors at least 15 feet away.

Use a heavy tripod or attach sandbags to increase mass.

A good battery but I think a lot of batteries get changed needlessly. They actually last quite a while.

Reducing Light to the bottom half of the bullet Increases Sensitivity. By a LOT!

BLT and I have were having problems with errors and failure to see shots with 2 different shooting chroneys. BLT gave me his shooting chroney and bought a new CED Millennium 2 Chronograph and still problems continued. Dillon customer service had suggested a black tarp under the chronograph but it was the CED instructions talking about "Glints" that got me thinking. A nice shiny bullet is going to reflect everything around it. If the bullet is reflecting as much light as the Sky Screens transmit, It Won't Be Seen by the Chronograph.
I glued some black velvet to 2 14x20" sheets of foam core board. I tested yesterday and out of 200+ shots I had 1 error.
22g 2400 NOE 429421 .431 4" Colt Anaconda 1494, 1493, 1499m 1505, 1493, 1499fps, ES 12fps
25g 300 MP Lyman 429421 6" S&W 629 1432, 1404, 1375, 1395, 1349, 1358fps, ES 83fps
BLT found some cardboard and black paint and soon had his CED Chronograph close to 100%.
This is the Shooting Chrony that took 2 22LR shots, so sports a new front plate.

I had posted elsewhere but this may be the spot. The chronograph readings are to show the accuracy. This really works. Thanks to BLT Sandwedge for the "used" chrony and the research he did in contacting Dillon etc. Thanks to You, in this forum, for all the help. And the pictures: