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A discussion of (velocity measuring) chronographs, including the (sort-of) new Garmin Xero C1 Pro. Login/Join 
Freethinker
Picture of sigfreund
posted
Being able to measure the velocities of the bullets we fire can be informative, useful, and sometimes important for various shooting disciplines. Like so many things these days, modern technology has given us the capability to do that to a degree that was literally unimaginable within living memory (of some of us, anyway).

Other than just curiosity, there are several possible benefits to knowing the actual velocities of our projectiles. Manufacturers often tell us what the velocity of their particular loads are, but one of the first things an owner of a chronograph learns is how often those claims are incorrect for their guns, and that they are commonly exaggerated. Deliberate false claims are probably less common than they were decades ago when no one outside of a ballistics laboratory had any reasonable way of measuring velocities accurately, but they are still possible.

Even if a manufacturer truthfully cites the velocity of a bullet obtained from a 26 inch rifle barrel or 6" pistol barrel, that’s still not of much use if our barrels are only 16" or 3" long—and that’s especially true if the manufacturer doesn’t tell us the length of their test barrels. If our barrel is the same length as the manufacturer’s, there can still be reasons why our velocities may not be the same as theirs, including variations among ammunition lots. One highly-respected commentator familiar with the process has pointed out that ammunition makers usually load for pressures, not necessarily final velocities.

Deliberate misrepresentation or not, there are countless Internet videos demonstrating that claimed velocities very often aren’t accurate.

So why do accurate velocity figures matter?
There are two basic reasons: external and terminal ballistics. External ballistics refers to the trajectory (flight) of the bullet to the target, and terminal ballistics refers to the effect of the bullet on the target.

Both types of ballistics can be important for rifle shooters because they want to be able to hit their targets at longer ranges and for hunters velocity affects energy, and energy affects how bullets perform on game animals. If, for example, a manufacturer says a bullet will expand reliably at X velocity or higher, it may be important to know whether it will still retain that velocity at Y distance. If we don’t know what the velocity was when the bullet left the barrel, we can’t begin to know how fast it will be going at Y distance.

As for trajectories, there are many ballistics solvers these days that will tell us, for example, where a bullet will hit at 550 yards based on a 100 yard zero for our ammunition, but they require correct velocity data input to be accurate.

Accurate knowledge is essential for handloaders who are trying to develop loads with most consistent velocities, and even for target shooters who may want to know if a “flyer” was due to poor shooting technique, a velocity anomaly, or some other factor.

For most pistol shooters, trajectories (external ballistics) don’t matter much, but terminal effects can be important when choosing among various loads. For example, based on my own measurements, I found one 9mm Luger “+P+” load whose velocity wasn’t as high as other +P loads, and not much greater than standard pressure loads I’ve measured. If projectile energy is important, then velocities are important as well.

If you’ve gotten this far and agree that knowing accurate projectile velocities is important, then how do we determine that ourselves? Ignoring the very early methods involving ballistic pendulums, the three basic chronograph types I’m familiar with are instruments that measure the time it takes for a projectile to pass between two optical sensors, those that use Doppler radar, and at least one that uses electromagnetic sensors.

The optical type includes the models by PACT and Competition Electronics. MagnetoSpeed uses the electromagnetic sensors, while LabRadar, the Garmin Xero, and others use Doppler radar.

The nonprofessional grade chronographs that measure the projectile time between two points are the oldest, and date back to at least models like the Oehler 35P. Today they are also among the least expensive and are still in common use. Most instruments of that type rely on seeing how the passing bullet interrupts the sensors’ view of overhead light from the sky or other source. Because reflections from bullets themselves can affect how the sensors react, most chronographs of the type have provisions for “sky screens” to be placed over them.

For the measurement results to be accurate, the optical chronographs must very accurately measure extremely short time periods and the accuracy is enhanced by spacing the sensors farther apart. I used a 4-foot spacing with my Oehler units, and as I recall it was possible to set them for up to 12 foot sensor spacing. Most such optical units today use much shorter spacing, and that may be partially why they have a demonstrated reputation for questionable accuracy along with lighting and reflection issues.

Such optical instruments are relatively inexpensive and are often easy to set up and use. They must, however, be positioned in front of the gun, and that can be an inconvenience at public ranges that limit going forward of the firing line. Depending on the type, it’s also recommended that they not be placed too close to the gun to prevent false readings (or even damage) due to the muzzle blast.

The MagnetoSpeed chronograph is very popular and has the advantage of not requiring the instrument to be down range from the shooter. The “bayonet sensor” is an extension placed just in front of the muzzle, and it’s evidently important that the sensor extension be positioned very carefully. The MS chronograph is most commonly attached directly to the rifle barrel, and that extra weight near the muzzle plus its effect on barrel harmonics can affect the accuracy and precision of fired rounds. That issue can be corrected by various aftermarket brackets that attach the bayonet sensor to the stock of the rifle, but it’s something to be aware of, as is the fact that things like handguards around an AR or similar rifle barrel may make it impossible to use the unit at all. And I say “rifle” because that’s all the MS chronograph can readily be used with. It can’t normally be used with pistols. I assume it could be used with shotgun slugs, but I haven’t seen that demonstrated.

The LabRadar was the first consumer level chronograph I’m aware of to use Doppler radar to measure bullet velocities. Its advantages are that it’s easy to set up (if a little fiddly); it’s completely behind the muzzle of the gun; it can measure the velocities of things like pellet guns and even arrows; and, most uniquely, it will measure the downrange velocities at increasing distances. The last can be useful to compare measured velocities with what a ballistic solver app will tell us the velocity should be at, for example, 70 yards.

The LabRadar starts measuring when a projectile enters its radar field after it’s triggered by the muzzle blast of the firearm. The device also has provision to be triggered by movement of the gun under recoil by use of a sensor that’s attached to the gun. That’s the method I normally use with rifles, but it’s necessary to adjust the sensitivity of the LR because even operating the bolt could trigger the unit and lead to a “no reading” notice that requires the nuisance of resetting the unit. There are some other inconveniences with the LabRadar, but once we become accustomed to them or develop work-arounds, they are minor.

So, now the teaser in the title of this thread: The Garmin Xero chronograph.

The Xero also uses Doppler radar but in a more convenient way than the LabRadar. First, it’s far smaller and lighter than the LR. With its little tripod I can easily find room to carry it all the time in a range bag. It also seems to be much less finicky about being aimed at the target than the LR that even has an aiming notch. It doesn’t require any sort of triggering, and just identifies and picks up the projectile in flight with its continuously-transmitted beam. The LR instructions caution about things like how a metal target can confuse the radar beam, and if that’s a concern with the Garmin, it’s not mentioned. It provides only one velocity readout, but—if we can believe it—with 1/10th of a foot per second precision.

I haven’t used my Garmin too much yet. I was a little surprised by the readings in the one centerfire rifle session, though, with large measured velocity swings from a load that hadn’t ever exhibited that. I will be watching that in the future, and if I think there’s a problem with the unit, I’ll check some readings with other units. The unit had no problem with an airgun, and, somewhat amazingly to me, it even measured the velocity of plastic pellets from an airsoft P226: a five shot average of 274 fps, with a standard deviation of 1.8(!) fps.

The biggest disadvantage of both the LabRadar and Garmin are their prices which are much higher than the other units’. Another factor with both is that they require the projectile to travel farther before a reading is obtained. As I recall without checking again, the Garmin wants about 20 yards of travel, and based on my experience with short range testing, the LR needs probably about the same. If we’re trying to measure velocities in a test of a ballistic medium at 10 feet or so, they won’t work.

Not everyone needs a velocity-reading chronograph, but some excellent units are available for the purpose these days. This discussion is, of course, only an introduction, and shouldn’t be used for any final decisions about which to choose. Also keep in mind that the examples discussed aren’t the only options available.

Added:
There are many video reviews of the various chronographs, but this is the best I have thus far found that shows side by side comparisons of the LabRadar, MagnetoSpeed, and Garmin. The performance of the LabRadar was a little eye-opening for me, although as the narrator points out, some of the test shots involved unusual and difficult conditions for a radar unit.
https://www.youtube.com/watch?v=ypT8zjSEG9w

Added 2:
If interested in another radar unit, the FX True Ballistics (I believe that’s its name), this is a discussion:
https://www.youtube.com/watch?v=PDUwAioD2ZM
I have no experience with the unit myself. It does have some advantages over the others, but it is also by far the most expensive.

And to be clear, when I mention the LabRadar (which I own), it refers to the original. A much smaller LX model has been announced for release in the near future. I obviously know very little about it.

This message has been edited. Last edited by: sigfreund,




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Posts: 47422 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
3° that never cooled
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I've used chronographs for many years, just to satisfy my ballistic curiosity. The first was some type that, IIRC, produced a series of numbers with each shot. Then one had to consult a little booklet to determine what velocity the numbers indicated. Later, a friend had an Oehler, and I also used a couple PACTs. The Oehler and PACTs worked just fine. We put the Oehler and PACT in tandem one day to see if there was any significant difference in velocities recorded. There was not. I now use the Garmin. Even shooting close as 15 yards, never misses a shot. Quite impressive, and yes, rather expensive, but I have not regretted the purchase..


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Posts: 1567 | Location: Under the Tonto Rim | Registered: August 18, 2003Reply With QuoteReport This Post
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^^
I had the same chronograph back in the late 70’s, an inexpensive Oehler model. The sky screens had to be placed ten ft apart iirc. Kind of a pain, but it seemed to provide consistent data.


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Posts: 8770 | Location: UT | Registered: December 05, 1999Reply With QuoteReport This Post
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I now have the Garmin and consider it worth the money and a great convenience. My CE and CED phototransistor chronographs are pretty much retired. If I had a private range and could leave it set up, the CED has some good features, though.

My first consumer chronograph was an Oehler. Its Skyscreens, spaced five feet apart, had a detection area about 4" wide. I cut cardboard windows to line up through. Readout was by turning a knob through 12 positions, noting whether the dial needle swung to Yes or No and entering the appropriate digit. Then translating that output with the chart included. Phew.


quote:
most chronographs of the type have provisions for “sky screens” to be placed over them.


A case of mutation of the English language, kind of like "Series 70." Originally "Skyscreen" was the Oehler trademark for their photo detectors, not the diffuser shades hung over them. Now you call the shade a "sky screen".
 
Posts: 3292 | Location: Florence, Alabama, USA | Registered: July 05, 2001Reply With QuoteReport This Post
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I started with a Chrony. It was OK....better than nothing.

The Magnetospeed works for me. Once I found out that one port on the device produces better readings than the other, I now get very consistent data. It has worked well with all my calibers, even subsonic 22lr with match lead bullets. I don't find that it negatively affects accuracy, as some of my most accurate groups have occurred while the unit is clamped to a silencer. POI changes are minimal -- maybe 1/4 to 1/2 MOA down, but only on my thinnest profile AR15 barrels. I haven't felt the need to measure handgun MVs, so that disadvantage with a Magnetospeed is not an issue for me.

Labradar hasn't worked for my suppressed rifles. I'll never buy one. Moving on....

I use a chronograph to obtain MVs for rifle loads, for external ballistics data -- i.e. bullet flight dope. Once I have that info, the chronograph stays in the box until I experience down-range bullet flight changes. Meaning that the factory ammo has changed or my barrel is shot out. I don't bang away from fixed position at a single target, then compare individual MVs with impacts on targets.

Garmin's unit sounds interesting. I recall seeing the release a number of months ago, and I was interested to see real-world results. The unit sure seems to work well. Buying one isn't a current priority, but I suspect I will have one sometime down the road.

Garmin has done well with radar tracking of golf balls, so maybe is was just a slight stretch to move into bullet tracking. I have a Garmin G80, which is a rudimentary ball launch monitor and an on-golf-course GPS unit. The G80 tracks golf ball speed and club head speed with amazing precision, especially given its price. Buddies have Garmin's R10, which is a dedicated ball launch monitor. The R10 is among the most accurate systems for its price. It doesn't do the best at tracking golf ball spin RPM or spin axis, but it costs $600 versus the Trackman system that starts at $21,000 or so.

Garmin is doing something right.
 
Posts: 7895 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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