Ballistic Chronographs

Chronographs are an essential tool for load development in firearms.  An accurate measure of muzzle velocity is the cornerstone for understanding trajectory and sighting.  In addition, it is a very useful cross-check against the data in the loading manuals as you carefully increase propellant charge towards a safe maximum.

Up until the advent of the MagnetoSpeed range of ballistic chronographs, projectile velocity was measured by the passage of the projectile over the top of a spaced pair of optical sensors.  The nature of this detection system is that the sensors look directly skywards and detect the fleeting passage of the projectile passing above them.  Mostly, these units have diffuser screens above the sensor and the bullet must pass through the space between them.  They are designed for natural light and do not function under some types of standard artificial lighting.

These optical chronographs and their diffuser screens can be prone to error by varying natural light conditions.  That is particularly a problem for me as I shoot on the Atherton Tablelands where the weather is famously fickle.  We can toggle back and forth between bright sunshine and overcast misty drizzle in the space of minutes as the warm, humid breath from of Coral Sea gets pushed up to our colder altitudes by the coastal mountains.  Sometimes the units will not read correctly with the diffuser screens in place while at other times the screens must be in place for detection.

Typically, optical chronographs need to be placed no closer than 3 metres from the muzzle of the firearm, sometimes a greater distance is required with high velocity and magnum calibres as the muzzle blast can dislodge the diffuser screens.  The alignment of the chronograph has to be done with some care and it can be a lengthy trial and error process to get the device properly aligned on the bullets’ pathway from the firearm to the target.

At the rifle range, these issues with optical chronographs pose a significant problem.  When I need to set up a chronograph at the range I make a point of getting there half an hour before it opens to shooting so that I can make the, often, many trips back and forth between the bench and the chronograph.  Of course, once shooting starts, should the light conditions not favour the chronograph set up (diffuser screens on or off), then you are stuck until the next cease-fire.

A few months ago I was at the range, suffering a particularly frustrating morning where I was only measuring the MV of about half my shots.  As I sat there, steaming and waiting for a cease-fire, I idly watched one of the long-distance boys setting up to test some new loads.  After the rifle was all set and his gear laid out ready for shooting, he quickly attached a curious looking device to the end of his barrel.  Intrigued, I wandered down for a chat and encountered the MagnetoSpeed for the first time.

MagnetoSpeed V3 Ballistic Chronograph

From what he told me and what I subsequently read the MagnetoSpeed ballistic chronographs are easy to set up and fit.  What is more, they have a reputation for highly reliable velocity measurement.  The sensor detects the slight magnetic variation caused by the approach and passage of the projectile.  A voltage is generated that is proportional to the variation of the magnetic field.  The variation in voltage can be used to determine the exact moment that the projectile was dead centre over each detector.  The distance between the sensors is known to a precision of +/- 0.005 of an inch, which translates to a variation of about +/- 1 fps per 1,000 fps of MV.  And, of course, it measures as close to true MV as is possible, rather than 4 metres away.

I contacted the Australian agents, Huntsman Firearms in Townsville, to find out more about the MagnetoSpeed.  Huntsman turned out to be an interesting group of guys (see the insert box), but anyway more to the point they happily agreed to loan me the new V3 version for review.  Even better, they also loaned me their Oehler Model 35P Proof Chronograph to cross-check the MagnetoSpeed V3 against.  Yippee!

The MagnetoSpeed V3 Ballistic Chronograph is designed for barrel diameters of 0.5 to 2.0 inches and can also handle muzzle brakes up to 2.5 inch diameter and 3.0 inches in length.  It comes packaged in a small, compact plastic case.  The small instruction manual is logically laid out and well illustrated.  The case also contained a couple of optional extras, which I did not need.  There were the orange spacers which are slightly wedge-shaped for barrels with a pronounced taper.  Also in the box was an adaptor for rail mounting on handguns and short-barrelled rifles with Picatinny fore end rails.

The key to getting a good measurement from the MagnetoSpeed is in the correct alignment of the sensor.  Ideally, that is a gap of 0.25 inch between the projectile and the sensor deck.  An alignment rail is provided to check that separation.  The slight taper of sporting barrels is not a problem for the MagnetoSpeed, but common sense dictates that is wise to look down the bore of the firearm from the breech to confirm that the bullet is not going to clip the sensor.  A check of the separation is also easily done with a cleaning rod placed in the barrel.

The sensor is tightly held on the barrel with a strap system and a tightening knob underneath the sensor allows for that to be cinched up.  Once again, it pays to check that the sensor is not moving during shooting.  That is unlikely to be a problem if it is correctly fitted as the MagnetoSpeed V3 chronograph is capable of recording shot velocities at a rate of fire up 1,100 rounds per minute.  Crikey!  I am pretty slippery at reloading my Ruger No 1 single shot but reckon there is no risk of exceeding that constraint.

The V3 is capable of measuring air gun MVs too.  There is a 0.125 inch spacer provided in order to get closer to the sensor deck to pick up the passage of such small projectiles.  There is also a 0.375 inch spacer provided as well.

 

Comparison of the MagnetoSpeed V3 to other chronographs

Occasionally known for my excesses, I risked creating chrony-envy at the range by setting up three chronographs in series.  The MagnetoSpeed V3 was attached to the end of the barrel and, three metres out in front, I set up the big Oehler Model 35P Proof Chronograph.  Behind that, I placed my Alpha Master Chrony to take advantage of a great opportunity to check it against the others.  I fired a series of rounds from my 223 Remington, incorporating factory and handloads that represented a velocity spread from about 3,000 fps to 3,400 fps.  That data is represented in the table.

[table]
READING,OEHLER 35P,CHRONY,MAGNETOSPEED V3
Maximum fps,3326,3352,3356
Average fps,3124,3118,3153
Median fps,3116,3115,3141
Minimum fps,2989,2959,3011
Stnd Devn fps,111,130,124
[/table]

What that shows is close agreement between the three chronographs across that spectrum of MVs.  There was a slight difference between the units, but it was a consistent difference with the MagnetoSpeed V3 reading 20 to 30 fps more than the Oehler 35P.  The slight difference in position between the three measuring chronographs does have a small effect on the comparable velocity measurements.  For all intents and purposes that can be ignored as there are other factors with greater impact on the measured velocity.  However, for those folks who like precision, you would expect the Oehler and Chrony devices to measure a slightly lower velocity given they are slightly further away from the muzzle.  My ballistic calculation for the 55 grain .224 projectile used in the tests tells me that would be -6fps for the Oehler and -8fps for the Chrony when compared to the MagnetoSpeed.

I found the display screen simple and intuitive to use.  It switches on and off automatically when plug the plug is inserted and removed.  The home screen comes up by default and you can start shooting without any further ado.  The display presents the MV of the shot just fired and to the right of that the statistics for the string of shots so far.  Pressing the ENTER button brings up the main menu which allows for more advanced features to be accessed.  The sensitivity of the MagnetoSpeed V3 is variable over eleven different levels, catering for a wide variety of projectile types and speeds.  There are a couple of other modes of operation to cater for shotguns and rapid fire.  The memory card holds the data in CSV format (that is comma separated values) which can easily be extracted directly into the spreadsheet application on your computer.  The instruction manual also details the advanced modes that can be called on to update the firmware or troubleshoot the device in the unlikely event that there seems to be a detection problem.

The convenience of the MagnetoSpeed chronograph is that it can be easily fitted, and removed, at the range bench without having to wait for a ceasefire to move out and adjust the detector screens.  There is a downside to the MagnetoSpeed as well.  It cannot be used in conjunction with group shooting because of the influence it has on barrel vibration and the point of impact.  In my sporter weight rifle my POI at 100 yards moved up about 100mm and to the left by about 30mm, while the group size increased noticeably.

In addition to the V3 model, MagnetoSpeed also makes a Sporter model which is more basic and is about half the price of the V3.  The V3 has a lot more features that may not be required by every shooter.  Like most modern electronics the V3 has downloadable firmware updates.  The battery compartment is easily accessed without tools and offers the choice of either one 9Volt or two CR123s for power.  The recommended 2017 Australian retail price of the MagnetoSpeed V3 Ballistic Chronograph is $625.

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