How do Chronograph owner-users verify device accuracy?

How do Chronograph owner-users verify device consistency from year to year or month to month?

How do Chronograph owner-users determine when device is failing, but not yet failed, to report accurate velocities?

In terms of velocities reported by a chronograph, what is a realistic variance from "actual" velocity?
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To my mind this set of questions is analogous with those of vernier micrometer's measurement veracity. In this instance, though, having access to a set of standards ("Jo" blocks) is comparatively easy and modestly priced.

I compare results between different chronographs, while being used simultaneously.

For example, Magnetospeed on the barrel and a PACT Profesional at 10 yds, or using a PACT in tandem with a CM2.

Chronographs do differ. Bryan Litz has published his comparison studies.

Me I could care less if my chrono read 3045 and it should be 3085 as long as it reads 3045 all the time. Or close.

I have used 22lr to insure I'm reading in the right range.

I have check against other Chronos. As long as it repeats and isn't 100s of fps off I have other things to worry about.

Yes I too use subsonic 22LR to check my chrony every so often as these are manufactured (usually 1065fps) to be just below the speed of sound and are most likely quite consistent in velocity. being a dark lead bullet and not going too fast they are going to be easy and consistent for the sky screens to pick up.

I have found in practice that the above seems to work well. I used to put through the 22LR subsonic at every chrony session but now I have faith that all is well and I have a pretty good idea with the loads I use and try just what velocity range I should be seeing with various cartridges.

I use my Feinwerkbau 300 S air rifle. I chrono'ed until I got tired a couple times in the garage. 570, 570, 570, ad infinitum.

honestly?

i checked with some 22 when i first got one, like 10 rounds, then when i got my second, like 2,,, i might have bothered when testing 3-dozen when I was doing loads of evals...

today - looks, its not anything that can be calibrated - and extraordinary results just mean I shoot them over a second chrono ...

for example, when i first got over 2400 with the AccRels -- and 416 rem, back in the day, i didn't trust my results, i shot them over another chrono - sure, it could take a couple weeks to get with a friend to do so, but it also allowed me to see

truth is, other than screen deployment, ALL of them call for 1/2 percent 0.005 and aren't actually "adjustable"

I've never been that concerned with absolute accuracy of a chronograph, in my eyes it's kind of like my volt meter. If my volt meter reads 224 volts instead of 230 I am unconcerned and the overall outcome is the same.
I operated just fine for many years without a Chronograph so having one is a help but not an essential. I still build my drop tables for my hunting rifles with actual shooting at 100, 200, 300 and 400 yards.

Accurate velocity determination matters, if you're a long range shooter and pride yourself at killing game at ~1000 yards.

Suppose you've chronographed your loads at ~3000 fps at 70oF, but you find yourself hunting Wyoming after a cold front and the temperature has fallen to zero oF...what's your velocity at zero. You'd better know within reasonable tolerances, if you plan to hit something at 1000 yds on the first shot.

You can SWAG it assuming a certain temperature sensitivity, and you may have even determined your temperature sensitivity between 70oF and 50oF, but can you extrapolate to zero...I'm not certain you can with the accuracy you need to hit sometime on the first shot at 1000 yds.

For me, the best solution is the use the Magnetospeed chrono, which is accurate, light, and compact and can be used easily in the field at zero oF.

I suggest buying the Magnetospeed chrono as a second chrono to double-check your current chronograph, correlate the two, and transport the Magnetospeed to the field to check your velocities when the temperature is or will likely be significantly different than when you did your at home calibarations.

The Magnetospeed could easily be taken to Africa or Mongolia or whereever as needed.

Given current technology, IMO the best set-up is to have the LabRadar and Magnetospeed chronographs, which have made the sky-screen chronographes obsolete, although the latter still work.

PS. I do not work for Magnetospeed or LabRadar.

quote:

if you plan to hit something at 1000 yds on the first shot.

Never have and never will.

I'm with Dave best way for a drop table is actual data.

As to the difference between 70deg and 0. Still best way is measure it at both or shoot it at both. What difference does it make if the starting velocity is 3040 or 2990? What matters is the difference.

Velocity and calculated drop is just an educated ball park guess in my opinion.

If taking your Magnetospeed along with you works for you by all means go for it.

quote:

Originally posted by ramrod340:

quote:

if you plan to hit something at 1000 yds on the first shot.

Never have and never will.

I'm with Dave best way for a drop table is actual data.

As to the difference between 70deg and 0. Still best way is measure it at both or shoot it at both. What difference does it make if the starting velocity is 3040 or 2990? What matters is the difference.

Velocity and calculated drop is just an educated ball park guess in my opinion.

If taking your Magnetospeed along with you works for you by all means go for it.

Paul,

If you're not a long range shooter, precision is not that important for you, so why bother.

The apps are very accurate and work incredibly well, when properly used. I use one (Strelokpro) every time I practice (from 400 to 900 yds), and I'm amazed at how accurate it is.

Tables cannot cover all the myriad of possibilities encountered in the field. The apps have made the tables obsolete, except for maybe helping the slower folks understand the basics concepts of long range shooting.

AIU

quote:

except for maybe helping the slower folks understand the basics concepts of long range shooting.

Yep that is me.

If the apps are now accurate enough to be useful great. I've found the ones I've used to be in the ballpark at the ranges I care to shoot(500 or less). I have never seen much less tried Strelokpro

Back to the initial question. Is it critical to know your velocity is exactly 3000 and 2950 at zero deg? Or is it critical to know that the velocity dropped by 50? I have always "tweaked" my results to more closely match actual testing. Same as I tweak the burn rate as an example in QL to more closely match end results.

I use my Chrono to help look for SD and order of magnitude for a load bullet etc. If my go to load reads 3000 and my new test load reads 2900 I stay with the 3000(assuming it is accurate) Or like Jeff what range of velocity am I actually getting from a wildcat.

I will also admit to being old enough that I use my phone to make calls and since I can't hear it anyway texts to the kids and grandkids. Other than a game or two have never downloaded an app unless the kids or wife did it. Yep just and old fart.

As I've always said a shooter needs to do what makes him comfortable and gives him confidence in his shooting. So what if others question the value.

AIU Please help this old fart. I stole this from their user manual

Truing

Suppose, you input muzzle speed as 2648 f/s. Shoot at distance bigger than zero distance. Suppose this is 800 yards. Calculated elevation for this distance is 26 MOA.
Find out REAL elevation is needed to hit the target. Suppose this is 27 MOA. On the trajectory validation screen input Distance as 800 yards and Elevation as 27 MOA. Tap button "Calculate" and speed at which elevation will be equal 27 MOA will be calculated. It this case, it will be 2609 f/s. Tap button "Use this velocity" and this calculated speed will replace your current cartridge speed (2648->2609) and screen will be closed. On the main screen tap "Calculate" button and you will get calculated elevation which equals REAL elevation and equals 27 MOA Now you can input any distance and hit the target.
MV temp variation – Optional field.Powder burnrate and resulting MV are temperature dependant. You may get higher MVs in summer heat and lower in winter cold. This field specifies in percent how much MV changes within 15 degree temperature change. You can leave the default 1.5% (2,5% for metric units) if you are not sure of you powder properties, or put any figure in a range of 0,5-3,5%

Is this not basically tweaking the app to adjust for your actual data? Would this not be more accurate than any Chrono velocity? Just trying to understand this NEW STUFF.

Paul,

First, the further away and the smaller the target, if you expect to hit that target on the first shot, the closer one has to be to inputting the actual MV, BC, air temperature, ammo temperature, target distance, absolute barometric pressure, wind velocity and direction, etc. Being "close" is not good enough.

Also, gun precision and accuracy become more-and-more important with greater distance and smaller targets. Moreover, your scope better track true and your ballistic reticle better be marked accurately for the magnification your using.

You know all this stuff, but this is true, since the trajectory is much flatter for the first 500 yds vs the second 500 yds. As the trajectory begins to rainbow the target hit window narrows. It's easy to hit objects up to 500 yds, but much harder at 1000 yds.

IMO, ammo temperature sensitivity is not an easy thing to get a handle on. First, in my area I don't see wide temperature extremes between zero and 80 oF. Nonetheless, I have tried measuring temperature sensitivity by shooting between 90 oF and 70 oF, which is not enough of a swing in my opinion; and, often my results just don't make sense. The designer of Strelokpro says a good powder should have a temperature sensitivity of ~0.5%.

Also, how do you measure ammo temperature...ambient air temperature or with a hand-held infrared thermometer. One should use an accurate infrared thermometer. Do you have one?

With Strelokpro you can true-up either velocity or BC.

You would think BC's are well established, but this is not always the case. Bryan Litz's velocity determined BC's are usually always less than manufacturer reported BC's. Why is this? I don't know. Litz's BC's imply that Nosler and Sierra don't know what they are doing. But, I've found that the manufacturer reported BC's seem to predict trajectory better than Litz's. I assume the two are determined using different techniques.

I favor using bullet drop data as the best means of determining BC, but Litz disagrees and he uses velocity decrement over distance. The increasing availability of Doppler radar may iron-out these differences. Theoretically, with the new LabRadar one could determine your own BC, for the first ~150 yds of bullet travel.

As a result, I true-up BC rather than velocity. Especially, since I can get an accurate velocity at the range or in field with my Magnetospeed chrono. With the Magnetospeed on, the point of impact only varies slightly in my experience.

Getting an accurate MV in the field obviates the need to determing ammo and/or gun temperature sensitivity.

All these variables make long range shooting fascinating, and I haven't mentioned wind much, which can drive me crazy, especially where I shoot...variable gusting cross winds and up/down winds. For wind, I recommend a 338 RUM shooting a 300 gr Berger bullet...that is, minimize the SWAG

AIU

Thanks AIU for the time.

I knew there was a reason I don't shoot at 1000yds.

Problem with BC is it changes with velocity. So yes the manufacturer or software has one. But it changes. Maybe the software covers it.

Sounds to me you are doing and excellent job of TWEAKING to get your forecast to match your actual results. Sound more like me 25 yrs ago when I spent hours and many $$ to get that .75MOA hunting rifle down to .625.

Now days I simply don't shoot that far. So temp, air density, ammo temp etc won't move me out of minute of Elk. Looking back over the last 5 years I doubt I have shot longer than 350yds except for dogs. Then I simply adjust actual because there would be another dog any second.

If I were going to shoot 1000yd it would be at a range so again adjust for actual.

Enjoy your long range. You have a lot more patience than I do.

Thanks again for explaining.

Last question. Back to the OP question on velocity accuracy. Isn't it still relative? If you do all your adjustments for a "measure" velocity then because of temp, altitude etc isn't the change the velocity change the important number not the actual velocity?

I can see if you are making no adjustments then a perfect starting velocity is critical. Once you start adjusting aren't you also adjusting for the error in velocity?

Time for more

Paul,

I'm not certain I understand your question regarding MV, but the following are the deterministic variables required by ballistic apps or programs in rough order of importance...and these assume you and your gun are capable of shooting MOA groups and there is no wind.

1. Range to target
2. Zero range (and offset, if present)
3. Muzzle velocity
4. Ballistic coefficient
5. Absolute barometric pressure (absolute BP goes down as altitude increases)
6. Scope adjustment precision/accuracy (scope tracking)
7. Air and ammo temperature
8. Slant angle (shooting up or down hill)
9. Sight height
10. Spin drift
11. Cross-wind jump
12. Latitude/azimuth (Coriolis effect)

These 12 are deterministic variables, meaning they can be measured quite precisely. When measured precisely and input into ballistic programs, the programs are very accurate. When you have these 12 accurately determined and entered properly into a first-rate ballistic program, you'll hit your target with high percentage from the very first shot. Of these 12, I have the least confidence in the reported ballistic coefficients, and that's what I true for when trajectory appears different from predicted.

Even wind can be estimated and accounted for, but given the gusty variable nature of wind, this is - by far - the most difficult part of long range shooting. Experience reading the wind and using very high BC bullets helps most here, as well as a bit of luck (SWAGing) and having a good spotter. With training you can spot for yourself and learn to read mirage patterns in SWAGing the wind.

Regards, AIU

I must apologize to the OP for sidetracking his question.

What I was trying to ask. Say you go out and measure the temp at 70 and velocity as 3000. You get a forecast of drop etc. Say you were a touch lower than forecast. You tweak the BC. Are you not potentially accounting for a slightly lower than measured velocity?

Using that new BC you go out same range same everything but temp so it is now 30deg and your velocity measures 2950. You run a new forecast that uses a velocity 50fps slower.

Actual velocity might have been 2980 the first time and 2940 the second. But you adjusted out the velocity error.

So once adjusted the first time the 50fps difference is what makes the difference.

I think it is time to give up and stay MO elk.

Paul,

If you go out and measure air temp at 70 and MV at 3000 fps, I assume you know what you're doing and air temp is exactly 70 and your MV is 3000 fps. You've double-checked your thermometer and chronograph and you trust them to give you true and accurate data.

Now, if your trajectory is off, then one of the other 10 deterministic variables is in error; and, IMO likely the BC. Thus, you true for the BC.

When you true-up your app, true for the variable, whose measurement you trust the least.

Since, I double and triple check my velocities, I trust my velocity measurements; but, I cannot measure the BC of the bullet, which I must take from the manufacturer or Bryan Litz, neither of which ever agree with each other. How do I know who's correct??? By trueing BC, I determine my own average BC.

Also, if things remain askew, double or triple check your zero point, scope, range finder, barometric pressure, true ammo temperature determined by a infrared hand-held thermometer, etc.

If all your inputs and aim are perfect, a good ballistic program like Strelokpro will put you on target essentially every time.

They are that good!!! Our military snipers developed these programs, likely after much time and expense.

Regards, AIU

PS. With LabRadar sitting next to your barrel or by having Magnetospeed attached to your barrel, you can have velocity measured everytimg you fire. The Magnetospeed will cause a slight impact point change, but it's not much. Labradar has no effect on impact point. If these instruments are showing a consistent bias, then your adjusted BC will correct for that...maybe this is the answer to your question. Moreover, by measuring velocity everytime you fire, who cares what you ammo temperature is, you know the velocity.

Obviously, you can't have Labradar or Magnetospped set-up when you shoot at the elk at 1000 yds, but the evening before the hunt - when the temperature will be close the opening morning - you can let your ammo equilabrate with ambient temperature and fire a few with the Magnetospeed attached. Then you know very close to what your actual temperature adjusted velocity will be the next morning. You enter that value into your app, which will then automatically adjust for temperature the next morning. Don't fire ammo that's been warmed in your pocket!

If you decide to get serious about this, you should buy a Kestrel. In fact, I'd get the model with blue-tooth capability, then your iphone app will read directly from your Kestrel for temperature, wind speed, wind direction, humidity, and barometric pressure. Humidity is negligible though.

Paul:

No need to apologize. I appreciate ancillary information as much as I enjoy furnishing it.

One of my pet expressions from my time teaching remedial students in high school is: "You asked me what time it is, and now I'll tell you how the watch works."

quote:

Originally posted by ramrod340:
I must apologize to the OP for sidetracking his question.

What I was trying to ask. Say you go out and measure the temp at 70 and velocity as 3000. You get a forecast of drop etc. Say you were a touch lower than forecast. You tweak the BC. Are you not potentially accounting for a slightly lower than measured velocity?

Using that new BC you go out same range same everything but temp so it is now 30deg and your velocity measures 2950. You run a new forecast that uses a velocity 50fps slower.

Actual velocity might have been 2980 the first time and 2940 the second. But you adjusted out the velocity error.

So once adjusted the first time the 50fps difference is what makes the difference.

I think it is time to give up and stay MO elk.

Another factor in all this that has not been discussed is Altitude.
Yes I know this is a sidebar from the original question but I find it as important as Chrono accuracy or temperature.
In my neck of the woods my shooting range resides at 6,800 feet above sea level. I shoot at my range in any weather ranging from mid teens(15-17) to high 90's.
I Antelope hunt at this elevation or lower to 4800 ft.
I typically Deer and Elk hunt at higher elevations around 8,000 to 11,000 feet elevation, but can Sheep and Mountain Goat hunt to slightly above 14,000 feet above sea level.
If I go to Texas or Africa to hunt I am more likely to encounter 200 or 300 feet above sea level.
My personal opinion is these deviations in altitude and relative humidity will be far greater than any potential inaccuracies in my chronograph.
Just another angle to consider.
I practice at my home range regularly at 400 yards and under (all positions down to 25 yards)
With some occasional shooting slightly beyond that.
I consider myself "ready" with this practice and information to accurately engage targets at any distance to 450 yards IF all conditions are right ( lighting, wind, rest, angle, am I winded or rested, animal still or moving, etc...)

I tend to agree with Snellstorm in that I sight my rifles in 3" high at 100 yards, 4" high at 200 and on at 275 depending on caliber and see no need to shoot beyond 450 yards at most and only under ideal conditions, as I am not trained in 1000 yard shooting,nor feel the need, as the option itself removes the part I love best, and that is hunting as opposed to shooting...

I only use my chronographs to work up max loads and to satify my need to know the muzzle velocity of my reloads and the factory stuff..

Most chronographs today are accurate enough to satisfy my needs I have two. I only test them on rare occasions against each other, and they are always very close.

I would never be so annal as to check the weather then have to chronograph and resight my guns for a day of elk hunting, I get up to early and am on sight to hunt before daylight, not to mention the weather can change from summer to below zero every damn 30 minutes in Sept/Oct. Idhao. My primary problem is how to dress to keep warm without having to remove and put extra clothing!!

I speak only for myself, and hold no malice for those who chose other methods of bringing home winters meat..I might seek training for long range shooting at some point, but doubt that I would ever be inclined to hunt big game as such.

I've seen guys mount two chronys in line so the numbers can be compared. The oehler 35 has 3 screens for this very reason: it gives two numbers for each shot, and alerts you if they don't agree. When I first got the oehler I put it in line with a chrony and they agreed. The lighting does make a difference. The ideal chronograph conditions I've found are on an overcast day without the shades on the sensors. Under these conditions, my oehler will report numbers that are within 4fps of each other, always with the last screen reporting the lower number, which actually agrees with ballistics calculators.

I have never had reason to doubt numbers from this setup. I've used the results to calculate trajectories out to 2000 yards and the actual drop was spot on. Usually, advertised BC numbers are a bigger issue.

Chronographs are useful for people who play at long range, and for people working up handloads. It's another way to check a load against various published sources.

There is a reason the Oehler 35 is considered the standard for chronographs. As jpl said, three screens, two chronographs internally automatically comparing results and will notify you something is wrong if the results are too far from each other. Not cheap, but the best available.