Chronograph comparison

[taliv]

a month or so ago someone was asking about chronos in the SB and I related my experience from memory and I misremembered a bit so I wanted to attempt to correct that info, as I found my data from years ago and also repeated the experiment this week.

shot some rounds over two chronographs at the same time this week. The chronos were a "Chrony" and a "CED". They were positioned less than an inch apart and a little more than 10' from the muzzle.

The rifle was a 338LM and the breaks between the lines below indicate different loads as my friend with the 338lm is in the process of load development with several different bullet weights. So while the loads aren't all that great, they are informative about how the chronographs compare. I'll leave it to the reader to draw any possible conclusions.

The max difference across 15 rounds was 18 fps. That is 0.63% of the mean of the 15 rounds.
The mean difference of the 15 rounds was 5 fps. That is 0.18% of the mean of the 15 rounds.

chrony CED delta
2928 2926 2
2938 2929 9
2928 2928 0

2494 2494 0

3007 2989 18
3012 3000 12
3009 3002 7
3014 3009 5

2704 2696 8
2681 2674 7
2679 2678 1

3043 3039 4

2833 2817 16
2813 2804 9
2796 2790 6


I found this interesting because I did this test using a different shooting chrony in 2005. The only difference in tests was that they were spaced about 6" apart. However, I found in that test the CED recorded consistently higher velocities, with the summary as follows:

A sample 15-shot group has the following
Max difference 45 fps
min difference 35 fps
Mean difference 39.5 fps
Std. dev. 3.4 fps

Next week, a friend is supposed to receive an RCBS chrono and I plan to shoot over all 3. I'll report back if the results are interesting.

 

[Chilo]

Re: Chronograph comparison

I'm in the market. This is good information to have. Do keep us posted as to what you find. Thanks.

 

[normbal]

Re: Chronograph comparison

thanks. my Chrony B-master just went tits up again (sent it in for calibration last year and I'm still getting bogus/useless numbers). Considering the CED or a competition pro chrono but haven't yet decided.

 

[gstaylorg]

Re: Chronograph comparison

I appreciate your posting this info. Howvevr, am I missing something? In the two columns of numbers you posted, it looks as though the numbers underneath the "chrony" (at left)are higher on average, rather than the numbers underneath "ced" (at right", as you stated. Is this correct, or am I misreading your data? Thanks!

 

[taliv]

Re: Chronograph comparison

That is correct. There were two tests 6 years apart involving 3 chronos.
2005: chrony 1 vs ced 1 --- ced was higher
2011: chrony 2 vs ced 1 --- chrony 2 was higher

 

[Bearwalk]

Re: Chronograph comparison

Suggestion:

Move your chrony's 15 to 20' from the muzzle, especially for a 338LM. I have found that muzzle blast can impact your data at less then 15' depending on the rifle/cartridge.

Correct both of your chrony measurements back to the muzzle. I typically add 10-15 fps depending on bullet characteristics and distance from the muzzle. You'll also find that 3-5 fps of the chrony measurements difference is do to the spacing. I use a ballistics calculator to aid in the corrections.

I have the same two chrony's and use them back to back. Typically, I get a max difference of 10 fps and an average difference of 2-5 fps. Corrected.

 

[PaulStafford]

Re: Chronograph comparison

I have been looking at chronys too. I am dismayed by the marketing for them. Rather than disclosing the accuracy of the unit, these companies all seem to focus on extra calculations (knockdown power etc) which can easily be done later in excel.

I am surprised by the close spacing of the windows. 16" (1.33') seems average. At 3000 fps, that is a 440 microsecond period. To obtain 1 fps accuracy/repeatability, that requires timing to 0.15 microseconds. Are they that good? They need to be if we are making decisions or getting upset about +/- 10 fps dispersion, and still be measuring bullet MV rather than chrony accuracy.

Does anybody know?

 

[taliv]

Re: Chronograph comparison

bearwalk, sorry for being dense but i have no idea what you are saying.

I'm not trying to figure out what my muzzle velocity is. I'm trying to compare chronographs. So I don't think i need to correct back to the muzzle. The chronographs were positioned 1" apart. The speed of the bullet doesn't change much from 10' to 12'. (If i'm reading the jbm data correctly, it drops about 5 fps over the 10' from muzzle to chrono, so another 2 feet would be 1 fps difference.

3-5 fps of measurements difference is due to what spacing?

Frankly, I trust the chrono measurements a lot more than I trust ballistic coefficients.

what is the max and average difference of your chronys before you correct for it?

 

[Fred_C_Dobbs]

Re: Chronograph comparison

PaulStafford, the only two chrono manufacturers I've seen accuracy claims on are Shooting Chrony, who claims "better than 99.5% accuracy", and PVM, who claims "Accuracy: < 1% from the shown value." Considering the PVM's timing clock is 16x as fast as the SC's, and the PVM's screen are very slightly further apart than the SC's, either PVM is being very conservative or SC is peddling wolf tickets.

The Shooting Chronys have a screen spacing of 1 foot and clock speed of 1MHz.

The Competition Electronics ProChrono Digital has a 1.33MHz CPU and a screen spacing of 1 foot.

The CED M2 has a clock speed of 48MHz and screen spacing of 2 feet.

The Oehler 35P has a clock speed of 4MHz and screen spacing is adjustable from 1 to 15 feet (but it only comes with a 4-foot post).

The PVM-21 has a 16MHz clock speed with (I think) 14 inch screen spacing.

I can't find clock speed specs for the PACT Pro XP.

 

[taliv]

Re: Chronograph comparison

Fred, good info. Thanks. the ced also allows you to go out to 4 and 8' and maybe something else.

The rcbs results were interesting today. I'll post them when I get home

 

[Bearwalk]

Re: Chronograph comparison

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: taliv</div><div class="ubbcode-body">bearwalk, sorry for being dense but i have no idea what you are saying.

I'm not trying to figure out what my muzzle velocity is. I'm trying to compare chronographs. So I don't think i need to correct back to the muzzle. The chronographs were positioned 1" apart. The speed of the bullet doesn't change much from 10' to 12'. (If i'm reading the jbm data correctly, it drops about 5 fps over the 10' from muzzle to chrono, so another 2 feet would be 1 fps difference.

3-5 fps of measurements difference is due to what spacing?

Frankly, I trust the chrono measurements a lot more than I trust ballistic coefficients.

what is the max and average difference of your chronys before you correct for it? </div></div>

taliv, you are far from dense...I typically use a larger spacing than you do, 4-6', partly due to the tripods I use...If you are getting yours very close, then yes only about 1-2 fps difference is due to spacing. However, you are getting much larger differences than I even before correction. I'm guessing muzzle blast may have affected your results. Before correction, I will get a max difference of 15 fps.

BTW, not sure if it makes a difference here, but I use the IR's and a cover with my CED.

 

[Fred_C_Dobbs]

Re: Chronograph comparison

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: taliv</div><div class="ubbcode-body">Fred, good info. Thanks. the ced also allows you to go out to 4 and 8' and maybe something else....</div></div>
Not any more. The CED Millennium was adjustable out to 8 feet but only had -- IIRC -- a 4MHz clock. The M2 still has the readout on the screen for the adjustable screen spacing but the keypad is missing the adjustment button. You could run the screen out to 8 feet but the timer still would calculate it as 2 feet.

Actually, that still would cut the error rate by 75%. You'd just have to multiply the readout by 4 to get the real velocity but the adjusted number still would have just 1/4th the error rate of the 2-foot screen spacing.

 

[Fred_C_Dobbs]

Re: Chronograph comparison

I've not used the Oehler but I think I've got this bit straight. It has three screens that comprise two separate timing circuits. So if you run the screen spacing out to 15 feet, the proof screen goes in the middle and it clocks the bullet twice, separately, over the distance of 7 1/2 feet. That's an important distinction to accuracy because, all else being equal, a timing over 7 1/2 feet will have twice the error rate of one over 15 feet.

 

[taliv]

Re: Chronograph comparison

ah, bearwalk, i understand your point and yes, i wish i had wider spacing. I also wish i had the IR setup. I may get that someday when i get some spare cash.

Fred, that's interesting. My CED is a fairly ancient one. As many times as this one has been shot, maybe I'm due for an upgrade.

So today was not so good for the CED. I compared it to an RCBS. The CED was closer to the muzzle and about 2" away from the RCBS. The fedex guy dropped off the RCBS about an hour before the shots below were fired, so it is brand new.

So on the 7th shot, the CED failed to pick up the shot. On the 8th shot, it registered something pretty wild, and then it didn't register another shot for the remainder of the day. I don't know why this would happen, but it was fairly late in the day and it's possible the sun moved down far enough just at this time that it wouldn't work. I was not using the diffusers on either chrono and it was sunny today, though as I said, the sun was low in the sky.

CED RCBS delta
2952 2907 45
2944 2936 8
2930 2926 4

3029 3025 4
3065 3005 60
2994 2990 4
---- 3018
3148 3026 122

(I fired another 10 or so shots after this and the RCBS picked them up but the CED didn't so there's no point in listing them)

so what is interesting here obviously, though the sample size is small, is the 4-8fps delta on most of the shots, with 3 of them just wildly different.

 

[mtn grizzly]

Re: Chronograph comparison

I have found my CED to be very sensitive to low sunlight conditions and others have had the same experiences. Morning shooting with the sun at my 6 is really difficult on the CED - even if the entire unit is in the shade and has a clear view of the sky ???? My best friend sent his back (very pissed off) and got a 35P He is now in chronograph heaven!

 

[TEC]

Hard Data on Chronograph comparison testing?

Hello. New here. Recreational shooter, .223, 308 bolt actions. Reloader. Re-upping this thread after some on-line searching for good data I can't seem to find.
There are lots of opinion posts, this or that chronograph - works well, etc, but surprisingly little hard data (that I can find) where heads-up testing was done, as .

I have an F1 Chrony, originally purchased for testing air rifles. I am not sure I trust it. It's old and has absorbed a couple of pellet hits, but seems to still work -- sometimes -- if I hold my mouth just right.

Before investing in another, has anyone else done careful comparison testing of, the 3 or 4 brands one commonly sees for sale on the net? Anyone know of a source where results of independent testing was done?
Supposing that my own Chrony F1 is working "just fine", given the variations I see, is there a clever way I haven't thought of to test a chronometer for accuracy, or to calibrate a chronometer if it is off? Thanks.

TEC

 

[Pinecone]

I have been looking at chronys too. I am dismayed by the marketing for them. Rather than disclosing the accuracy of the unit, these companies all seem to focus on extra calculations (knockdown power etc) which can easily be done later in excel.

I am surprised by the close spacing of the windows. 16" (1.33') seems average. At 3000 fps, that is a 440 microsecond period. To obtain 1 fps accuracy/repeatability, that requires timing to 0.15 microseconds. Are they that good? They need to be if we are making decisions or getting upset about +/- 10 fps dispersion, and still be measuring bullet MV rather than chrony accuracy.

Does anybody know?

That is why I got an Oehler. 4 foot screen spacing for the main screens. It also has an intermediate screen at 2 feet to "proof" the main reading.

Oehler is what is used by most ballistics researchers.

 

[FALex]

here ya' go. Just spend the dough up front and be done with it.

https://www.riflesonly.com/pro-shop/superchrono.html

 

[DrEvil]

here ya' go. Just spend the dough up front and be done with it.

https://www.riflesonly.com/pro-shop/superchrono.html

I'm looking to buy my first Chrono... Do you have first hand experience with the Super Chrono? Worth the extra cash? Trying to map out my .408 and its being a PITA.
Thanks.