Range Report How accurate is your chrono??--

[rvander1]

I have a CED M2 Chrono, and I think it has limitations that i should mention.

I use a Kestrel for weather, using GPS altitude to get station pressure, and i use Sean Kennedy's Shooter Ballistics program. I had used the CED to input muzzle velocity, which is obviously critical at longer ranges.
I recently had a problem that made me think that chronograph accuracy may be the weakest data in my whole system. If my chromo is accurate to 1% (at least looking at the CED website tonight- I couldn't find instrument accuracy data, but i remember 1%)-- then my MV of about 3000fps has a chromo error of either +/-15fps or +/-30fps (if the accuracy of the CED M2 is +/-1%).
Yes, I guess shooting a bunch of rounds over the chromo may average out to a much truer muzzle velocity-- but i just don't know. Either way, my ES on the chromo will show 30-60fps (which is pretty terrible for long range) even if the gun inherently has a much lower ES-- like 10FPS. This larger ES could give me the false impression that my load isn't the best -- when it might be near perfect.

So for me, the chrono gets me in the ballpark, I zero in at 100, then shoot at 560yds (range on my farm), and dial inKestrel and Shooter output, and if this puts me high or low at 567yds, I adjust the MV input in Shooter Balistics until I'm dead on at 567yds.
This worked for me when my gun was unexplainably shooting 6" low at 567yds. I just dialed down the MV input in Shooter Balistics from 2945 to 2880, and the gun was on at all ranges. My Shooter output dialup at 567 went from up9.5 to up10.5.

Thoughts?? Does anybody else do this? Anyone else do this or wonder about that 1% chromo error at long ranges?
Bob

--

 

[Fred_C_Dobbs]

What a chrono does is so extreme, it's pretty much beyond the abilities of mere mortals to verify its accuracy, unless they have access to some pretty specialized test equipment. Even having multiple chronos doesn't get you any closer to the truth because you could shoot over two or 20 simultaneously and all that would tell is is how different they are from each other.

But before you list your CED on Craig's List for $25, let me ask about a couple of points that you didn't mention in the OP.

Did you measure your HOB with care, or did you accept the ballistic program's default value?

Have you shot the "box drill" with this scope to verify how closely its "clicks-up" values match its specs?

How confident are you the BC you are using is accurate? A bad BC is just as likely to skew the calculations as chrono error. For starters, are you using a G1 BC or a G7? Which model does your bullet best match?

Second, not every manufacturer bases BC on range data, some rely on computer modeling. So you could be using a BC with a built-in error.

And third, BC is not a static number. It changes with bullet velocity. A more comprehensive ballistic work-up will produce a different BC for 3-5 different velocity regions. If the manufacturer whose bullets you are using only publishes a single BC, that increases the likelihood that it will be wrong, based on your particular MV and atmospheric conditions.

Bullet drop is a function of time of flight. So if you know your HOB is correct, and your "clicks-up" are accurate, then the time of flight the app is calculating must be wrong. That ToF is based on MV and BC, so instead of assuming the MV is wrong, try tweaking the BC instead. Tweak the BC to make your range data match your field data. Then repeat at a second range to validate the "corrected" BC.

I think I'm pretty familiar with CED's data regarding the M2, and I don't recall ever seeing any claims of accuracy. A few years ago the German defense department tested your M2's predecessor, the Millennium model (M2 stands for 2nd Millennium). According to their tests, using .223 Rem and .45 ACP, the Millennium remained within 0.2% of the lab's value. But the newer M2 has a 12x faster processor (48 MHz vs 4 MHz), and 40% better sensor sensitivity, which at the very least should substantially reduce the average error.

Then again, everybody builds a lemon now and again (some more often than others), so it's not beyond the realm of possibility that your chrono is a bit wonky.

 

[rvander1]

Thanks, Fred, for your response, here's some add'l info--

To answer a few of your questions:
I measured my HOB a couple years ago, as carefully as I could- Shooter shows 2.125" (I think you're referring to Height of Bore --right?)
Bullet-- I use a 142gn Sierra HPBT Match King (Sierra #1742) and I use the BC's from their website --They are G1 and there are four-- all four have been put into the Shooter program. I really don't know if there are G7 BC's for this bullet and I don't know how accurate the Sierra G1 ballistics are. Don't know if there measured or computer modeled.
Yes, I have shot the box drill and my scope/clicks are right on.
---I had not thought about the fact that the BC's being off could do the same thing as the MV being off-- thanks for that! The only trouble with tweaking the BC's is that there are three of them in play between the initial MV of 2880 and the MV of 2057 at my 567yd target-- so which to tweak and by how much? Seems to me that all three might need to be reduced slightly to "bend the flight curve" and overall increase the TOF to match my field data-- but what would this do at other distances?? guess, as you said I would have to get more field data using the new BC's that work at 567yds.
-- Do you or, for that matter, anyone else on this forum know how good the Sierra G1 Ballistics are, or if there are better ones to use--maybe G7s for this bullet?
--Your info about the Germans using the first CED and it's accuracy to .2% is very helpful.
Much appreciated,
Bob

What a chrono does is so extreme, it's pretty much beyond the abilities of mere mortals to verify its accuracy, unless they have access to some pretty specialized test equipment. Even having multiple chronos doesn't get you any closer to the truth because you could shoot over two or 20 simultaneously and all that would tell is is how different they are from each other.

But before you list your CED on Craig's List for $25, let me ask about a couple of points that you didn't mention in the OP.

Did you measure your HOB with care, or did you accept the ballistic program's default value?

Have you shot the "box drill" with this scope to verify how closely its "clicks-up" values match its specs?

How confident are you the BC you are using is accurate? A bad BC is just as likely to skew the calculations as chrono error. For starters, are you using a G1 BC or a G7? Which model does your bullet best match?

Second, not every manufacturer bases BC on range data, some rely on computer modeling. So you could be using a BC with a built-in error.

And third, BC is not a static number. It changes with bullet velocity. A more comprehensive ballistic work-up will produce a different BC for 3-5 different velocity regions. If the manufacturer whose bullets you are using only publishes a single BC, that increases the likelihood that it will be wrong, based on your particular MV and atmospheric conditions.

Bullet drop is a function of time of flight. So if you know your HOB is correct, and your "clicks-up" are accurate, then the time of flight the app is calculating must be wrong. That ToF is based on MV and BC, so instead of assuming the MV is wrong, try tweaking the BC instead. Tweak the BC to make your range data match your field data. Then repeat at a second range to validate the "corrected" BC.

I think I'm pretty familiar with CED's data regarding the M2, and I don't recall ever seeing any claims of accuracy. A few years ago the German defense department tested your M2's predecessor, the Millennium model (M2 stands for 2nd Millennium). According to their tests, using .223 Rem and .45 ACP, the Millennium remained within 0.2% of the lab's value. But the newer M2 has a 12x faster processor (48 MHz vs 4 MHz), and 40% better sensor sensitivity, which at the very least should substantially reduce the average error.

Then again, everybody builds a lemon now and again (some more often than others), so it's not beyond the realm of possibility that your chrono is a bit wonky.

 

[Rob01]

Have you shot the "box drill" with this scope to verify how closely its "clicks-up" values match its specs?

That is what most people who use field data to figure their velocity don't check or think of. If that wasn't checked I would believe the chrono, as long as it's a quality unit, until it is checked. But even then there are other variables like the BC mentioned that will come into effect.

I only have 400 yards at home and I run my ammo over my chrono and run my data on JBM and have never been off more than .2 mils at 1000.

 

[MitchK]

Bob,

What you're doing is right on. You're trueing the ballistics calculator. When you input muzzle vel and bc, consider that a starting point. When you shoot at distance, like at your farm, you can make real time adjustments. It doesn't really matter what your mv is, what your bc is, or what your click values are. You are adjusting your "system" to real data, the bullet impact. The impact don't lie.

 

[D.ID]

Bob,

What you're doing is right on. You're trueing the ballistics calculator. When you input muzzle vel and bc, consider that a starting point. When you shoot at distance, like at your farm, you can make real time adjustments. It doesn't really matter what your mv is, what your bc is, or what your click values are. You are adjusting your "system" to real data, the bullet impact. The impact don't lie.

What he said +1K
My crono is retired, My numbers always match up and are then adjusted for conditions from the PROVEN base.
D.O.P.E...............The oldest, cheapest, easiest and most reliable data possible.
.
.
Many an internet argument was started over that statement right there.

 

[Six Feet Under]

I have owned 3 of them- They were all junk. Maybe you can find a good one for 1K- mine were shit.

 

[Tx_Flyboy]

i second six_feet_under.

My CED is a piece of shit...only worked for a little while and gives me error messages...even with IR screens it's still super-sensitive to light. worst investment i ever made.

I now have a magnetospeed V2. I cant wait to try it out...hopefully all the rave reviews are right on.

Ditch your CED, get a reputable chrono and verify the MV against your bullet impact.

Most people only focus on MV, however, variables such as SD and ES are more important to long range loads than MV alone.

A crappy chrono like the CED can give you bad data on SD and ES leading you to believe that you have a load that'll hold good elevation at 1000yards.

 

[Hogstooth]

I had an Ohler 35 that I used for personal use and for my classes, I had already noticed that while using it for my personal guns that it would read 20-25fps faster than what my actual velocities were during field shooting, this also was confirmed during my classes that I taught over the years. I have switched to the Magneto and it is pretty much spot on from what I can tell and has been giving me accurate readings so far, I have only been using it for 6 mo. or so. I would say that it is +/- 5 to 8fps which is way better than the Ohler which was giving me 20-25 over, but to the Ohlers credit it gave consistent readings and you could consistently take off 20 to 25 and be very accurate. Both have given consistent SD and ES readings, which is important for doing your load development.

 

[Tempest 455]

Magnetospeed, pretty accurate. Just shot it at 100, 500 and 1,000 the other weekend and dope was pretty much right on. However, crap in, crap out as others have stated. Got to have the right environmental data in your program.

 

[Sapper524]

I have a CED M2 and while its light years better than the POS "shooting chrono alpha" I had before, its still far from consistent. Overcast conditions vs Sunny conditions with the same load in the same rifle and proven data to 1200 yards show up to 60-80 FPS difference on the chrono readout. I have stopped relying on the chrono for my final velocities but to find a node close to the velocity range im after. I then refine it with atmospheric data and rounds on paper at 400 - 500 - 600. I then build DA dope cards for said load and run with it. I am hoping the Magnetospeed V3 (on the wait list) will shorten this process a bit. I however agree with the above statement, DOPE in its true form is the best answer In the long run, time consuming as it is, its the only thing I really trust.

 

[Fred_C_Dobbs]

Yes, HOB is 'height over barrel.'

Sierra's BCs are developed from range data. Bryan Litz's data on the same bullet is here (if you aren't familiar, Litz is chief ballistician for Berger Bullets, Grand Poobah for Applied Ballistics, and member and frequent poster of the Hide). He gives his own range-tested G1s, as well as his G7 BCs for it. But he has chosen different velocity regions from Sierra's, which prevents directly comparing his G1s to theirs. But by all means, plug in his G1s and see if you fare any better.

As MitchK writes, the ultimate objective is to tweak the system so it produces relevant data. And the only data to be trusted implicitly is the bullet, because it never lies.

IMHO, it is a better practice to tweak just one parameter, or at the very least, just one at a time, beginning with the parameter in which you have the least confidence. Without getting into G1-vs-G7, if your ballistic program will accept a G7 value, try Litz's G7 on that bullet with your range data. See if that gets you any closer.

If it does not, you can run with the theory that your chrono is reading 2.89% too fast (85 fps out of 2945). But to be certain, you need to compare results at at least one other range -- the further from the original, the better -- using the same tweak. A single point of data does not make a trend. If the correction does not hold at alternate ranges, that isn't the answer.

If tweaking MV doesn't straighten it out, as an alternative tweak, trust your chrono and tweak the BC instead. Then it's the same drill, test at at least two ranges. Like everything else in this process, BC is just a tool, not a holy relic.

You didn't ask but if I thought my M2 was off by that much, I'd be banging on CED's door before the warranty ran out. As you continue to test this load, I would suggest you gather as much data as possible. I've never had to deal with their customer service but it stands to reason that they will be more receptive to complaints of chrono errors if you can snow them under with data. If you remain convinced the chrono is off, especially by that much, there's no harm asking.

 

[leadbullet]

My crony is garbage, third one in a few years and always off, the last one by over 150 fps.

 

[stang02]

I have a cheap pro chrono pal. I don't shoot comps but I do like to hunt on my property. I have a 403 yrd shooting lane and I shot 175 fgmm. I chronoed it at 2465.5 with my jp psc12 .308 20". shooter said I needed 9 moa at 403 yrds. I shot 5 and averaged around 4" high. I input that correction into shooter and it adjusted my mv to 2565.5. I used that new mv and shooter now said I needed 8.1 moa and I dialed 8 moa and shot 3 shots downrange at a 3" circle target. 2 out of 3 were inside the 3" target and one just outside. I'm happy with the results and I'm looking forward to clearing another 100 yrds at my shooting location. I come to learn that field data verification is the way to go.

 

[Rthur]

I have had a 35p for a few years. I have a few friends with same. We have tested them side by side with the same load/rifle. They have always given the same numbers. While this proves consistency it can't prove accuracy. I have used the velocity numbers from the 35p for dope and haven't been off by more than + or - .1 mil.

R

 

[Mod Adahy]

Chonys have always been junk. I have not seen a good one. Magneto looks to be the way to go.

 

[F4D]

I have the Magneto Speed V2 and have found the MV readings to be so close to actual field data from 100 to 1000 yards that I trust it completely.

 

[BryanLitz]

Most chronographs are capable of measuring velocity spread and SD pretty good. This is good for load development when you're measuring consistency.

However, most chronographs are not good at measuring the true average velocity. For example, it's common for a chronograph to say your MV is 3000 fps with an SD of 10, when your actual MV is 2970 with an SD of 10 fps.

As a rule, the units based on longer sensor spacing (2 feet or more) will get closer to your true average velocity, while the shorter ones (chrony, pact, etc) typically miss average MV by more than 10 fps. The CED is right at 2 feet so it usually gets average velocity within +/- 10 fps. One thing to watch out for with the CED is windy conditions. The folding mounting rail is relatively flimsy and when the wind catches the skyscreens the whole thing can dance around; bending and twisting. This puts the sensor beams out of alignment and each shot is effectively going a different distance between the start and stop. This is most evident if you're looking at ES and SD on windy days, it's very difficult to get a low SD with a CED in the wind. Not because of your load, but because of the chronograph. I think the unit could be improved dramatically with a solid steel rail instead of the flimsy folding aluminum one.

For optical chronographs, the Oehler is best (it's typically set up on a 4' rail). But the CED is less than 1/2 the price and can usually give you 'good enough' numbers if you're careful using it.

The MagnetoSpeed is a very good unit in terms of both it's accuracy and precision (SD).

-Bryan

 

[tspearsrph]

I have a CED chrono ....NEVER uses it any more. Checked it in between an Oehler 35P screens and the CED read 200 fps slower! Called CED. They were NO help. I asked if
i could send it back and have them calibrate it. They said they do not do that. This has been 6-8 years ago. Now have the Magneto bayonet V2 and LOVE it.

 

[2Shots]

I have owned and shot over several brands of cronos over the years, since I bought one of the magnetospeed units I doubt I will ever use anything else. For me, doing load work up, checking velocity in different weather conditions it's so easy its hard not to like them. And so far I have yet to have bogus readings or not feel confident its not spot on. I can take a just scoped rifle, bore sight it, fire three shots, have the scoped zeroed in and have initial speed data in 5 minutes, way easy. Sold me on them. Now if I made my living working for a bullet company and had to have dead nuts accurate data like somebody we know, maybe I would think different. But if I break mine I'll buy another.

 

[Ro_Bird]

I'll add my vote to the magneto Speed as well. Hands down easy to use and set up. Generally velocity tends to be with in +/- 10 fps.

 

[Kirkd]

That is what most people who use field data to figure their velocity don't check or think of. If that wasn't checked I would believe the chrono, as long as it's a quality unit, until it is checked. But even then there are other variables like the BC mentioned that will come into effect.

I only have 400 yards at home and I run my ammo over my chrono and run my data on JBM and have never been off more than .2 mils at 1000.

This has been my experience as well. I have noticed .2 mils as well. I just end up jotting that down in my log book and I know I have my zero at that distance.


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