Chronograph accuracy & consistency?

[Naphtali]

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?
***
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.

 

[OKFC05]

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.

Not really. With a quality chrono, the chance that the electronics are a "little off" is very small. When the electronics go, they usually crash.
The real problem is in the placement and lighting on the sensors, which is usually where the failed to read, false reads, and systematic errors come in.
If you can afford it, the OEHLER dual chronograph uses dual readings and is considered the industry standard for personal use. Our club owns one, and it is a real joy to use.
Oehler Research, Inc.--Model 35 Proof Chronograph
From the Oehler 35 specs:

ACCURACY:

The expected error on any one shot depends on both velocity and screen spacing. Typical errors are shown in the table. The table assumes good light conditions, dark bullets, exact screen spacing, and shooting through the center of the Skyscreen III window. Actual errors under your shooting conditions will be reliably indicated by the PROOF CHANNEL


2 FT screen spacing, 1000 fps mean, 3 fps error (0.3%)

Screen placement: Shooting too close to the screens will cause the sensor to read the shadow of the muzzle blast and give false readings.

Lighting: An unshielded sensor looking straight up into pure dark blue sky will not read, so translucent covers are needed, and supplied. Sunlight directly into the sensor is bad. In the shade on a cloudy day is perfect.
Sensor distance: Since the chrono is a timer, any error in distance between screens causes errors.

You can check for gross errors with a know cartridge, but checking the internal electronics calibration requires a laboratory, and physical errors in setup can be corrected on the spot.

Many of the perceived "chrono errors" are human errors in chrono setup or handling of the firearm. With most pistol loads, pointing the gun up to settle the powder to the rear and carefully leveling to fire gives significantly higher speeds that pointing the muzzle down first, for example. Doing it first one way and then the other gives a high variance.

 

[fredj338]

There is little correlation between actual vel readings & what the ammo manf stated vel. Ime, a good chrono doesn't lose its reliability or accuracy. Setup up properly, good screens, same gun & load, accuracy will vary only by daily variations of temp, altitude & humidity, for years.
In back to back to back testing of 3 diff brands of chrono, they all gave vel within 10fps of each other. The diff in brands is ease of getting the readings from shot to shot (fewer errors).

 

[flintsghost]

The replies to this question are pretty much right on point and correct based on my use of two different units I found lots of problems at our club range. Lighting and atmospheric conditions being the greatest variable. This is one reason why I personally tend to rely more on manufacturers information and have quit using home chronographs. I also tend to take the data provided by other home users, which will vary in large degrees both from each other and from the manufacturers, with a large grain of salt. Especially those who constantly denigrate the ammo that I use for self defense and which I have seen results or studied the reports of LEO shootings.

Manufacturers don't purposely provide false information. They do however, take lots of readings from pressure test barrels instead of actual firearms. Pressure test barrel readings will always be higher because they are normally a closed breach system and don't bleed gas like revolvers or normal fitted semi auto's. These are not used for all calibers and also most companies that publish loading manuals will state exactly what they did use.

 

[Naphtali]

Many thanks, guys, for clear, detailed replies. I especially appreciate OKFC05's identifying one of the most reliable chronographs available.

All of you have a pleasant, safe Easter.

 

[Mike SC Hunter]

I've owned and used my OEHLER 35P for over twenty years....proof channel gives 2 velocities for every shot......Flags those vastly different with an *......I trust it completely........Won't use anything of lessor quality.

 

[Twoboxer]

Many thanks, guys, for clear, detailed replies. I especially appreciate OKFC05's identifying one of the most reliable chronographs available.

All of you have a pleasant, safe Easter.

The Oehler has long been the gold standard for optical chronos, but I thought I'd mention that there are other types besides optical chronos.

MagnetoSpeed makes a magnetic chronograph, embedding two sensors in a plastic bayonet you attach to your firearm's barrel. It's takes seconds to install, sets up when the range is hot, and works an any weather, any light or no light at all. Because the two sensors are an unchangeable distance apart, differences in how you attach it (set it up) cannot cause noticeable variations in readings. Either you get the correct reading, or no reading at all. It is also difficult to shoot this chrono, and there's no need to shoot through a narrow area at your targets.

The drawbacks are the bayonet cannot attach to all firearms, and when attached to a barrel the POI will most likely change.

New and still hard to get is the LabRadar. This is a Doppler radar unit that sits next to your firearm on the bench, or on a tripod next to you. The unit responds to the sound of your shot and measures the velocity of the projectile it picks up. Yes, it sets up when the range is hot, can be used indoors, outdoors, in any weather, in any light, and with other shooters present. It can measure any solid projectile from arrows to 50 BMG and shotgun slugs, but not shotshell (yet). Like the MagnetoSpeed, it is extremely difficult to shoot this chrono, and there's no need to shoot through a narrow area at your targets.

Drawbacks are it costs as much as an Oehler, is new in the field, and is currently in significant backorder.

 

[fredj338]

Manufacturers don't purposely provide false information. They do however, take lots of readings from pressure test barrels instead of actual firearms. Pressure test barrel readings will always be higher because they are normally a closed breach system and don't bleed gas like revolvers or normal fitted semi auto's. These are not used for all calibers and also most companies that publish loading manuals will state exactly what they did use.

Well, while not false, certainly misleading. Many vel readings are done in longer bbls than what most of us use. Then take into account all barrels/chambers are diff, there can be a 50fps diff from guns that appear identical. The only way to know what the vel is on your gun, is a chrono, yours or a clubs. I've used many diff manuf but my Oehler by far the best.

 

[MarkL_01]

<snip> Then take into account all barrels/chambers are diff, there can be a 50fps diff from guns that appear identical. <snip>.

I use a shooting chrony, and have found that setup is very important. Misalignment of the unit so that the bullet travels at an angle over the screens can easily make 50fps difference. It also tends to go crazy as batteries get weak.

Regarding different guns, 50fps is not at all surprising. I have a Ruger blackhawk with 6 1/2" barrel that consistently gives 100fps less than a 6" Ruger security six.

I was more surprised by comparing a 4" with a 6 1/2" 629-6. These were commonly within 50fps with factory or near-factory level loads.

-Mark

 

[Magload]

The Oehler has long been the gold standard for optical chronos, but I thought I'd mention that there are other types besides optical chronos.

MagnetoSpeed makes a magnetic chronograph, embedding two sensors in a plastic bayonet you attach to your firearm's barrel. It's takes seconds to install, sets up when the range is hot, and works an any weather, any light or no light at all. Because the two sensors are an unchangeable distance apart, differences in how you attach it (set it up) cannot cause noticeable variations in readings. Either you get the correct reading, or no reading at all. It is also difficult to shoot this chrono, and there's no need to shoot through a narrow area at your targets.

The drawbacks are the bayonet cannot attach to all firearms, and when attached to a barrel the POI will most likely change.

New and still hard to get is the LabRadar. This is a Doppler radar unit that sits next to your firearm on the bench, or on a tripod next to you. The unit responds to the sound of your shot and measures the velocity of the projectile it picks up. Yes, it sets up when the range is hot, can be used indoors, outdoors, in any weather, in any light, and with other shooters present. It can measure any solid projectile from arrows to 50 BMG and shotgun slugs, but not shotshell (yet). Like the MagnetoSpeed, it is extremely difficult to shoot this chrono, and there's no need to shoot through a narrow area at your targets.

Drawbacks are it costs as much as an Oehler, is new in the field, and is currently in significant backorder.

Yep I been waiting for mine since 15 Jan and they are now telling me April. I like the MagnetoSpeed it give good reading but doesn't work well with most handguns. I like my Prochrono the best and it is on a rolling stand and I can roll it out when the range is Hot. Our indoor range is always hot.

 

[Frank46]

I have an Ohler 35P with 3 sky screens on a 2' rod. I mount this on an old camera tripod. Of the 3 sky screens one is what they call a Proof screen. The velocities from the first two screens must more or less match what the proof screen sees. If not you get an error and in a string of shots you discount that shot. The P in 35P stands for printer. This is where all the magic takes place. It prints out the velocities in the order the shot was fired so you get and average of the lets say ten shots. Then you also get what is called standard deviation this is a figure that tells you basically how close the velocities are in relation to each other. The smaller the number means your velocities are very consistent. This last is all for the reloader, how he measures his powder, seating depth of the bullet,wether or not his primers are good. Lots of good info in that little box. So I'll give you an example, some folks say you do not need magnum primers in the 39-06 with IMR 4350 powder. My normal load is 55.5 slightly compressed load, 165 Nosler Ballistic tip, Federal case, IMR 4350 and CCI 250 large rifle magnum primer. I've been shooting this load for over 30 years so I know it's good. The standard deviation for my load is 14 and darned accurate. The only sad thing about bringing a chrono to our range is that one of two things happen. Some fool will be sitting at your bench waiting for the cease fire to end so he can shoot through your chrono. I have to explain that it is my chrono and you are not going to shoot through it unless you got about $700 in your pocket to replace it. Then another guy will let me shoot through it for him. And the next thing that happens is that every tom,dick,and harry will want the same. I've had folks take the spotting scope off my bench and this old fart was not in a happy mood when I finally took it back. Frank