Chronograph question

[billd]

I don't have a chrono and know nothing about them. Today I was at the range and the person shooting next to me had one. He invited me to try it. I fired 4 shots with my 42" .25 caliber, 20 grains of 3F and a .240 ball.  One shot registered 1777 and another 1802. Two shots did not register. One said "ERROR" on the screen, the other had no response.  The owner said it may have been the smoke that caused the problem. I was about 10 feet from the thing you shoot thru.
Do these speeds sound right?

Bill

[BrownBear]

I'm not sure about the speed, but can offer some hints for the failures.  I usually shoot at 15 feet.  And I've had trouble with small bullets (or balls) on bright sunny days, having to fashion shades to keep direct sunlight off the sensors.

[billd]

Yes, it was clear and sunny.
Bill

[Larry Pletcher]

The shades will help I think.  Smoke may have been a problem, but I've had more problems with patches.  A little distance may help both.

Regards,
Pletch

[Daryl]

The speeds sound just fine, Bill.  Failures to 'read' are generally attributed to the ball not being 'seen' as it passes over the eye. there are several reasons this can happen. One is bright sunny days with blue sky.  The dark sky 'protects' the ball from being seen as both are dark to the chronographs 'eyes'.  A lot of chronographs have diffuser screens white are opaque white in colour and the eye's pick up the projectile easier.  Concussion can also trigger a false reading, as can the ball not travelling close enough to the 'window' the eye's see. This is another visibility problem.  I set my chronograph's at 10' to 15' normally as 15' is the longest I can get and still have the controller box on the bench(length of wire). Concussion usually only rears it's head with handguns and the big rifles- ie: .458 and .375, yet I still get good readings with them. As to small projectiles, the .25 balls are relatively slow and not really very small.  My .17 rifles give no problems chronographing, normally, and run 4,000fps, yet the bullet is only .172" in diameter. That's small.
The diffuser screeens are the most important part of a descent chronograph for readings on sunny days.

[northmn]

Velocities sound OK.  Another thing that will give the error message is if the ball does not pass over both sensors.  My Chrony works best in bright light.  Patches and other stuff could screw things up.  The chronograph standard is 15 feet.

DP

[Maven]

Can't comment on the velocity, but I've also had problems with my F-1 Chrony on bright, sunny days:  It won't read when the sun is ~directly overhead even with the sky screens.  One solution is to use a tilt head tripod to mount the chrono. and then adjust it so that the device is ~30 deg. from horizontal (right or left depending on the position of the sun).  It's a bit more challenging to shoot through a tilted opening, but it often works.

[Mad Monk]

I once shot over a Pact Professional Chronohraph.  When Elephant went belly up I purchased a CED with the optional infra-red set up.

The "skyscreens" are set up around a photocell.  Some are photo active resistors similar to what you have in a home heating unit burning fuel oil.  The photocell forms one leg of a Wheatstone Bridge.

The resistance of the photocell, such as the cadmium sulfide cell, varies with the amount of light impinging on its surface.  These chronographs generally have a lens over the photocell that directs/concentrates light onto the surface of the photo-active resistor.  So when a projectile passes over the lens it changes the amount of light reaching the photocell which changes the resistance.  That quick change in resistance is picked up by the computer in the chronograph.  You have a start and a stop photocell supplying the time between screens to the computer.


Both my Pact and the CED are sensitive to direct sunlight getting past the "shades" mounted above the "skyscreens".  If the light is too bright the screens simply do not see the projectile passing above it.  Not enough of a change in resistance to trip the computer.  This was a problem at certain times of the day and more so in certain seasons.
I ended up having to rig white plastic trashbags over the "shades".  
One other club member would bring along an old wooden step ladder.  Mount the skyscreen unit on the paint can holder part of the ladder and then c-clamp an umbrella in a position to shade the skyscreens from anything but above lighting.

I bought the infra-red "shades" to use the chronograph on dark cloudy days.  When they worked well.  But on bright sunny days they were borderline useless.

The CED is very critical of how high the .45 or .50 caliber ball would be above the skyscreen opening.  About 6" was the max.  The Pact was not nearly as sensitive to how high above the skyscreen lens the ball would be in passing over the skyscreens.

I did all of my patched ball shooting with the Lehigh Valley lube or some other liquid lube.  In cold weather I had trouble with the Wonder Lube patches going through the chronograph still wraped around the ball or following the ball through a few inches behind.  Which gives error messages like crazy.  With the liquid lube the patches would come away from the ball as soon as the ball cleared the muzzle.  I would keep the skyscreen unit out at the 15 foot length of the cords back to the computer.  Usually my fired patches would be scattered a few feet from the skyscreen tripod.

If you shoot lubed conicals, such as Maxi-Balls over the chronograph don't be surprised to find lube sprayed all over and down into the skyscreens.  The Maxi's were still throwing Wonder Lube out of the lube grooves at the 15 feet distance.  I carried a bunch of cotton balls and Q-Tips to clean skyscreen lens anytime I had to shoot more than a few Maxi's.

Bill K.

[Daryl]

I have both the Pact and a Chrony Beta - both are best on overcast days with flat, white cloud cover, but I can generally get them both working on sunny days as well.  Bill's right about the height of the projectiles, the closer to the "Eye" the better, but the close to the eye, the narrower 'window' the eye sees.  Too, it can be expansive to hit the screens - but then who hasn't?  I'm on my third set for the Pact Timer - had it since 1982. The 'difuser' panels are only a couple inches wide and let sunlight in if it's anything but straight overhead, so Bill's idea of white plastic bags is a good one. I'll have to get some white bags from the Tire Shop.

[Maven]

"Bill's right about the height of the projectiles, the closer to the "Eye" the better...."

Daryl, That's been my experience as well, but you don't want to get them too close either!  (Don't ask how I know this!)

[Mad Monk]

I NEVER shot a skyscreen.  I can brag now that I no longer use the chronograph.  Never would have made such a statement when I was using it.

I found that to get the shot in the best position over the skyscreen I simply made a cardboard target that I attached to the first, or starting, skyscreen.  The cardboard had a hole in it where I wanted the ball to go through.  A slot rather than a circular hole.  No different than aiming at a regular target posting on a target holder.  You kinda forget there is a pricey skyscreen behind it so it eases the nerves when squeezing off a shot.

[Daryl]

Hit the wires of the chrony once - should have sighted the rifle in before shooting, but a .17 cal bullet at 4,000 fps makes a small nick, nice and clean.

Taking velocity readings at 100 yards for ballistic coefficient checks will result in more screen hits, if you do enough of it.

[northmn]

I totally blew away my first chronograph with a scoped 22 hornet TC Encore pistol.  I keep my current one behind two pieces of 1/4 inch angle iron.  Mine always worked best on sunny days and would not register too well on cloudy days

DP 

[Daryl]

Dark clouds generally hurt performace.  I still like the white plastic bag suggestion - thanks Bill.

[Mad Monk]

Dark clouds generally hurt performace.  I still like the white plastic bag suggestion - thanks Bill.

That is why CED offers the infra-red skyscreens.  They claim you can shoot over that chronograph set up in total darkness and it will still work due to the IR cells mounted in the skyscreen shades.

But in total darkness.  How many rounds before you blow the skyscreens away?

Bill K.

[Mad Monk]

Dark clouds generally hurt performace.  I still like the white plastic bag suggestion - thanks Bill.

Something just hit me.

You guys up North, closer to the Arctic Circle, have less sunlight to work with.  On dark days you might have to rent a generator and sun lamp to mount over the skyscreens.

[Daryl]

Even at 2AM, there's enough 'light' to see with a scope and sometimes by the moon, especially in the winter - not that I do a lot of chronographing during the 'cold' seasons.  That lets me chronograph for a month anyways, eh.