Competition electronics pro chrono FPS fluctuations.

[45Bravo]

I have a question.
I was using a friends pro chrono yesterday, and was shooting strings seeing how consistent "Shadow" my new 2240 carbine was doing after putting on a 10 inch barrel, and doing a poly port mod.

I was shooting at a target 25 yards away and using it as a reference point so I wouldn't shoot the chrono.

I was turning a consistent 508-511.
30 shots into the string, I shifted to the next target 2 inches to the right (at 25 yards) and the next shot was at 614, and then 611, but I was still hitting the bull.

I think if I had a 100fps swing in velocity it would change my point of impact.

And it was on a 1/2 used 12 gram cartridge..

I shifted back to the left target and went back to 509.

So I started trying a theory out, if I shot to the left side of the sensors, it read one FPS, if I shot to the right of center, it read another.
And if I shot right down the middle any little bit one way or the other the FPS was off by about 100.

So it became a matter of picking a side.

Has anyone else had a similiar issue or know what could be going on?

Thanks.

This is Shadow

[ptpalpha]

Very strange.  Is it possible that the slight difference in angle that your body shifted to shoot the second target made the digital "5" appear as a digital "6"?  Remote chance, I know, but that's all I could come up with.
Other than that, I got nothing.  I just got my Pro Chrono last week and have put about 100 shots through it, haven't experienced anything like what you're describing.  Maybe drop an email to CE?
-Paul

[grumpy]

You are supposed to change your point of impact when shooting through a chronograph. That is why you got the variance.

[nomobux]

You are supposed to change your point of impact when shooting through a chronograph. That is why you got the variance.

  You lost me. Care to explain that ?

[45Bravo]

I THINK grumpy meant to say you are not supposed to change..

My thing is how many of the air gun writers (videographers) do you see just point the rifle through the screens without choosing an exact point to aim at? (Rick Ustler for one) and he uses a CE Pro chrono.

If moving the projectile path left to right across the screens can cause ANY variation in readings, then 98 percent of your readings should be suspect...

[michaelthomas]

It's not so much a matter of right, left, or middle.....it's presenting the pellet at an angle over the plane of the sensors.  The thing works by using the time it takes to cross over both sensors, then formulating the velocity by a calculation.  The amount of time between the sensors is very, very small.....so any increase in the distance can result in errors of calculation.

If you measured the distance between the 2 sensors straight down the middle......then measured the diagonal distance.....you would clearly find the diagonal to be longer.  Shooting on a diagonal (whether it is in the horizontal plane or in the vertical plane....or both )at all will produce slower velocities compared to exactly straight and level over the sensors.

This is an experiment that I have been able to repeat very consistently. 

Shooting through the chrony at a long distance away makes it tough to get the alignment perfect.  This is the reason that so many people come up with drastically different BC's for the same pellets when testing this way.  You have to be extremely picky about the setup to end up with any valid information....and even then I'm not so sure.

Hope that helped,

Mike

[nomobux]

It's not so much a matter of right, left, or middle.....it's presenting the pellet at an angle over the plane of the sensors.  The thing works by using the time it takes to cross over both sensors, then formulating the velocity by a calculation.  The amount of time between the sensors is very, very small.....so any increase in the distance can result in errors of calculation.

If you measured the distance between the 2 sensors straight down the middle......then measured the diagonal distance.....you would clearly find the diagonal to be longer.  Shooting on a diagonal (whether it is in the horizontal plane or in the vertical plane....or both )at all will produce slower velocities compared to exactly straight and level over the sensors.

This is an experiment that I have been able to repeat very consistently. 

Shooting through the chrony at a long distance away makes it tough to get the alignment perfect.  This is the reason that so many people come up with drastically different BC's for the same pellets when testing this way.  You have to be extremely picky about the setup to end up with any valid information....and even then I'm not so sure.

Hope that helped,

Mike

  I'll buy that ......... and be a little more aware in the future.

[grumpy]

Sorry, thats exactly what I was trying to say. Too dang early !... Yes, do not move your POI when shooting through the chrony or you will get different readings.

I THINK grumpy meant to say you are not supposed to change..

My thing is how many of the air gun writers (videographers) do you see just point the rifle through the screens without choosing an exact point to aim at? (Rick Ustler for one) and he uses a CE Pro chrono.

If moving the projectile path left to right across the screens can cause ANY variation in readings, then 98 percent of your readings should be suspect...

[45Bravo]

Ok, I will buy the logic posted in post #5 above.
But truly, how many people put a level on the chrono to make sure it is truly level to the barrel, then a level on the barrel to Make sure there is no vertical error.

I was only shooting from about 4 ft from the chrono. The target was at 25 yards.

And MOST people don't go into that much setup/measuring
They just turn it on, TRY not to shoot the chrono, and put it somewhere across the screens.

I am just trying to see if anyone else has had this crop up.

By the way a friend shot his .303 with his pet handloads across the chrono, 4 shots, 3 were within 47fps of each other the other was 117fps slower.

If your error of say a 1/16 of an inch made a difference of ~100 fps at 500 fps
Wouldn't  the same error make a higher fps reading if the projectile was traveling at 2200fps?
Thanks for your input.

[michaelthomas]

I see.......I thought you meant that you had the chrony at 25 yards.

I don't see that much difference when slightly out of whack with my pro chrono at 3 or 4 feet.  I do have the IR screens, though.  They go a long way toward minimizing errors due to light condition variances.

If you felt like it, you could do the math and see what the maximum error by shooting diagonal could be with a given velocity.

Mike

[45Bravo]

I see.......I thought you meant that you had the chrony at 25 yards.

Mike

Oh heck no, for sure not with a borrowed chrono. 
Not even with one I bought.
I will let the Chairgun app give me the down range velocity. 
Smarter people than I wrote the program, while I do trust my aim, and my ability to put a pellet trough an area the size of the screen gate, I prefer to trust their computations.

Accidents happen and trusting their computations is less expensive. 

[Pappy]

A lot of valid points made in these replies.  I too have the same Chrony, and the infrared light kit.  I set mine up 2 to 3 feet away from the barrel, inside, and have not experienced poor results .... yet.  Your issues may be much simpler than what was posted .... just sayin', ..... If you are outside, without an infrared kit, as the sun moves, shadows can cause a variance in readings, as well as changing conditions from sunny to cloudy.  Also, this Chrony absolutely eats up 9 volt batteries.  The battery does not need to be "dead" to begin given missed or inaccurate readings, I see issues after 3 hours of constant use with brand new batteries .... I rotate 3 new batteries, and use the "tongue" test to see which battery has more kick.  In my basement once, the sun came in a window and streaked across the readers .... the chrony was very erratic until I covered the window.  Great chrony, but it does have it's little nuances.

Pappy

[45Bravo]

Actually pappy my next step was to try a new battery as its condition is unknown.

It never missed recording a shot, it was outside, and sunny.

My next purchase will be a chrono, but it will be one with a smart phone/tablet connection.
It gets tedious writing down the numbers.

Total I fired almost a tin of pellets across the chrono
Seeing where it was shooting with different weight pellets and preloads on the power adjuster.

[K_sqrd]

Instead of buying a new chrony you might take a look at this and see if it fits your needs.

http://www.chronoconnect.com/

[QVTom]

I did the math for you guys based on a shooting chrony dimensions.  Actually I hate trig., so I let the computer do it for me




The Magenta line is the the worst case possible, the path is 19.4".  The yellow line is more like the OPs conditions but exaggerated, the path is 14.2".  A perfectly aligned shot is 12".

Magenta error = 61%
Yellow error  = 18%

Alignment errors will read slower that actual velocity.  These examples are obviously worst case and I'd think an average misalignment would be in the 0 to 10 percent range.

Tom

[45Bravo]

I-sqrd
Like I said in the first post this is a BORROWED A CHRONO.

Also , it is the older one not the digital model.

I have used the chrono connect app with reasonable success.
On some of my guns, 3 of them have TKO's on them and the app just doesn't reliably register the start sound.
They are just too quiet.

On my other guns as long as you have a good loud stop plate, and no suppressor, and your measurements are accurate, it works pretty well. 

Caldwell makes one with compatible app, and a deluxe kit for $140ish. (Tripod,case,lights, cables and everything)
And one of the design engineers for that chrono is a member here. 

[45Bravo]

Thank you QVTom, for doing the trigonometry.
I was really hoping there would be no math, (but i knew there would be.)

so 18%=~92fps at 511, but it would be -92fps.
so in the low 400's.

I seriously doubt i am getting 614 off a stock valved 2240 with a 10 inch barrel and a poly port mod.

Stock with a 7.5 inch barrel it is rated at 460 fps with i don't now what pellet.
And i was turning 511 with 14.3 Premiers.

I am not so picky that I am fretting over the results.
i have the ballpark figure I wanted to know of where my mods had taken me.

I see sometimes in videos of gun test, while chronoing, they will have an oddball shot or 2 that is just way out there from the others.

I will try a new battery, make sure i am square and level with the sensors.
then shoot strings and then move the gun from left to right, making sure i am still square with the sensors, and see if i get a velocity shift as i move across the sensor area.

Just another good reason to shoot some pellets and burn some co2
(INCREASING my carbon footprint all in the name of fun...)

[Pappy]

The Pro Chrono with the USP connect kit is pretty good, IMHO.  Add the infra-red kit and you have a great indoor chrony as well.

[K_sqrd]

Just an FYI, Midway USA has the Prochrono Digital on sale till midnight tonight for ~$100.

http://www.midwayusa.com/find?promotionid=1074970&cm_mmc=pe_weekly-_-specials-_-specials_clickeremail_20140603_1-_-AdBlock02

[reefsnridges]

Okay, well this post answered a few questions I had for sure. FPS @ the muzzle (TX sitting in a rest same way every time) 10 shots revealed great consistency w/ES of 10.15 & SD of 3.16.  Then I sat the chrony at 50 yds and trouble crept in. Recorded 5 shots and this after quite a few error msgs, I decided the chrony wasn't in perfect alignment and went down range for a tweek.  The results after 10 recorded shots left me puzzled with an ES of 40.76 and SD of 13.89!  So I went from thrilled at the consistency from the muzzle to scratching my head @ 50?  Great post, gonna have to try this again and keep all things equal. Maybe literally stretch a string to get alignment as close as possible?  I'm trying to get the "Chairgun Pro" to yield accurate results I can use, but I'm not there yet.  Man this addiction is killer!