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Accuracy of Chronographs - ?


Widder, SASS #59054

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How accurate are the more well known Chronographs?

 

I've been using a ProChrono Pal (by Competition Electronics) for a few years.    Often, my  reloads seem consistent with load data.

 

There are times when I double, even triple check, my reloads and seem to get differences in velocities from previous readings.

 

NOTE:   I understand some readings can differ based on it being a sunny day vs a cloudy day, and even temperature changes.

But most of my chrono testing is done in similar weather condition.     And I try to be consistent in setting my Chrono at

8 ft. from muzzle.

 

What is it about Chrono's that give inconsistent readings, even with fresh batteries.

 

EDIT:   what gathers the data..... the sky screens or the diffusers (metal rods) ?

 

..........Widder

 

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I've had mixed results with my chronograph. It works to know speed approximately. I don't trust it anymore to be dead on. Its been off up to 300 fps with the same rifle loads tested with high dollar units. It times the shadow of the bullet crossing the first photo eye to the second. The chrony needs to be level. If not, it lessens the distance to the photo eyes and gives higher velocities than actual. Pretty much the same deal with the bullet crossing, it needs to be as level of a path as possible going over the chrony.  There are other options that are more expensive and accurate out there now all the way to radar... I'm not that into it. I just want safe loads in whatever I'm shooting. 

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I have very good/repeatable results with my Caldwell G2, and when my WB Power factor has been checked by a different chronograph setup it has been consistent with the records I kept regarding that particular batch. 

 

One thing to keep in mind is that has a great deal of influence the actual velocity measurement is density altitude, I.E. the air density corrected for non standard pressure and temperature.  The Density altitude correction can account for a considerable variance between day to day testing.  Hot low pressure days will result in faster velocities, over cold high pressure days.

 

I always record the current barometric pressure and temperature at which the chronograph reading were taken in my records (I have been accused of being OCD).

 

Setting aside the the previously mentioned considerations, temperature has a significant influence on powder burn rates, some powder is more sensitive than others but in my experience they all are affected to some degree.

 

F.S.

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Enclosing the chrono in a lidded box and using the IR LED light bars will greatly increase the consistency of the chronograph.  And the shooting holes helps to keep the shots perpendicular to the chrono.  This is the setup we've used the last four years in for ammo checks for the Missouri State Wild Bunch Championship.  It's worked well.

Chrono1.jpg

Chrono2.jpg

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2 minutes ago, Ozark Shark said:

Enclosing the chrono in a lidded box and using the IR LED light bars will greatly increase the consistency of the chronograph.  And the shooting holes helps to keep the shots perpendicular to the chrono.  This is the setup we've used the last four years in for ammo checks for the Missouri State Wild Bunch Championship.  It's worked well.

Chrono1.jpg

Chrono2.jpg

Don't your neighbors complain about shot ;location? ;)

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12 hours ago, Widder, SASS #59054 said:

How accurate are the more well known Chronographs?

 

I've been using a ProChrono Pal (by Competition Electronics) for a few years.    Often, my  reloads seem consistent with load data.

 

There are times when I double, even triple check, my reloads and seem to get differences in velocities from previous readings.

 

NOTE:   I understand some readings can differ based on it being a sunny day vs a cloudy day, and even temperature changes.

But most of my chrono testing is done in similar weather condition.     And I try to be consistent in setting my Chrono at

8 ft. from muzzle.

 

What is it about Chrono's that give inconsistent readings, even with fresh batteries.

 

EDIT:   what gathers the data..... the sky screens or the diffusers (metal rods) ?

 

..........Widder

 

Have you used your speshul lube on the abacus in the calculator section of the chronograph? ;)

 

Kajun

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13 hours ago, Widder, SASS #59054 said:

 

 

EDIT:   what gathers the data..... the sky screens or the diffusers (metal rods) ?

 

..........Widder

 

 

The data is collected by light sensors.  The metal bars and the sky screens are just there to give the optical sensors something to "look at" when it is very sunny out.  You can use the chrono without them (or even accidentally shot them off)  and it still works if the day is nice and overcast.    It measures velocity by the time difference between seeing a dip in brightness on the first sensor to the second sensor.     Since that is a known distance you get  v =  d / delta T.   

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2 hours ago, DeaconKC said:

Don't your neighbors complain about shot ;location? ;)

Only once. :P

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There is a chapter in Brian Litz's "Modern Advancements Vol. 1" on chronographs.  Quite interesting. I built a light box for my Pact a few years back and it improved results.  I also have the IR screens for both my Pact and my CED M2. One of the reasons the Oehler 35P had the best results was the 4ft. screen separation. Also the high quality of the light sensors. I am building a 10ft. rail for my new Oehler 35P this Spring. Here are the results: 

#1:  4ft. Oehler in light box

#2:  4ft. Oehler in natural light

#3:  Magneto speed

#4:  CED  M2

#5:  Pact

#6:  Shooting Chrony

#7:  Super Chrony

#8:  PVM-21

 

Some notes: The standard to get the correct speed was An Oehler 35P mounted on a 12Ft. rail with artificial lighting inside a building. While the magneto speed had very good results it has to be Perfectly placed in line with the barrel and rechecked frequently or the results drop off considerably.  The biggest problems with the Chrony units wasn't reproducibility, but the speed was considerably off.  The expensive PVM-21 had poor reproducibility and the speed was far off.  For precision reloading The Oehler 35P, the magneto Speed (with very careful attention) and the Labradar are recommended. For general use the CED M2 is the best value. The Pact and Shooting Chrony are also useable. The results from the Super Chrony and the PVM-21 were so poor they were not recommended.

 

The Labradar unit wasn't available for this series of tests but it has since been tested by many (including myself) and it is as good as the Oehler in most conditions. The Labradar also has the advantage of not having screens to shoot through and it doesn't matter about the lighting conditions. I prefer my Labradar as it is accurate and easy to use.

 

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One thing that can affect readings is if the shock wave (muzzle blast) reaches the "Start" screen before the bullet.  That can trigger erroneous readings.  In some cases when I was doing extensive testing, I would place a thin cardboard shield between the muzzle and the start screen, shooting through it, IF I had been getting erratic readings.  This shock wave effect was more likely with rifles that had shorter barrels and with slower-burning powders in same.

Stay well and safe, Pards!

Merry Christmas!

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When chronoing BP loads we used a screen between the muzzle and the chrony. Usually the screen was a piece of heavy cardboard with a window cut into it. Covered the window with a clear plastic sheet

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12 minutes ago, bgavin said:

Set at 10' away... I'm surprised that nice box doesn't have a bullet hole or two...

BTW, great idea.
Many thanks!

It didn't when I shot those pictures, but it has one now from testing a 1911 that shot 2 inches low.  Oh well.

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Widder, I too have interesting results depending on factors that I cannot nail down consistantly.

 

I have heard about Labradar and the only thing keeping me from buying it, maybe the cost.  Which in relation to most of my guns, is less.

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TN Williams called me and suggested I use BOTH mine (ProChrono Pal) and his chrono (Caldwell) back to back

and see what the readings indicate.    Considering that would save me some $$$ right now, that is a pretty good idea.

 

I agree with the good comments above.   Thanks,  Pards.     I like the box idea.

 

Another point that was mentioned is the distance from muzzle to 1st sky screen.    I've been careful in the past to

watch that, which is why I actually measure 8' from my muzzle to chrono when I set up the unit.

I shoot some hefty stuff in 10mm, 460 Rowland and hot .45 Colt loads in both of my Ruger SBH Hunters.

 

If any of you think 8' is too close, tell me.  I can move it out to 9 or 10 feet and still keep it twisted the sky screens.

 

Again, many thanks.   Merry Christmas everyone.

 

P.S. - I hate spell check.  Every time I type in 'chrono'  it changes it to 'chorine' .     

 

..........Widder

 

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Spell check will let you best the hello out some jerk who picks a fight with you... < grin >

On paper, I always see the 10 foot distance mentioned.
I don't have a dog in this discussion, so no opinion... just curiosity.

I understand the various chronos can be irregular depending upon the light conditions.
Another plus for the box, if it is artificially lighted.

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The only way for an individual to chrono a shotgun that I know of that works is the Labradar. There are some commercial $3K+ screen systems with a very large window to shoot through that would work.

 

There was a lot of work that went into the ratings I mentioned earlier in this thread. Both 224 and 30 cal. bullets were used. Over 30 sets of shots were used. It was noted that WHERE you shot through the window (left,right,center) even made a difference on most of the units. 

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It is easy to chrono a shotgun. If you pattern you shotgun you'll find that at 10 feet, the shot has barely separated from the shotcup. Remove the screens and place it under a popup awning. lower the awning so that it is about 3 feet above the chronograph.

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On 12/18/2020 at 7:20 PM, bgavin said:

Asking for a friend... how does a guy chrono his shotgun...  it seems to me the risk of damage is quite high...

I've used my Pro-Chrono on my shotgun with no ill effect. The pellet spread is small at the chrono distance.

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