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Topic:   General   |   PDAs   |  Rangefinders   |   Rifle Scopes   |   Chronographs

Recommended Chronographs
We have no recommendations at this time.
 

Optical Sensor Types - In general we are dissatisfied with optical sensor chronographs due to changes in calculated velocities as a consequence of ambient light conditions. Sometimes they will work and sometimes they will produce errant results. When the errors are severe enough, it is an easy matter to disregard the data. But if the errors are close to what would be reasonably expected, then this bad data may be excepted by the shooter who may not realize that the data or some of it is off by 20 to 40 fps.  Some optical units have attempted to solve the problems produced by differences in ambient visible light by going to infrared light. And while the results from these units are more uniform, even the higher priced infrared units cannot guarantee accuracy with every round sent over its sensors. Recently a colleague placed two very expensive infrared units back to back and sent round downrange through both simultaneously. He found a 20 fps difference in the reported velocities between them. There is really no way to know which of the two was accurately measuring the projectile speed or if both were wrong.


Magetospeed V1 - We spent a considerable amount of time evaluating the Magnetospeed chronograph. It seemed promising since it eliminated optical sensors in favor of magnetic sensors that would be triggered as the bullet passed over each. This is clearly a very handy and convenient device to use since it can be affixed at the  shooting bench during a shooting session. There is no requirement to set up a unit yards in front of the muzzle and align the chronograph unit between the target and rifle. Therefore, to obtain muzzle velocity only quickly and with a minimum of fuss, this unit is far superior to any of the photo-electric cell or infrared devices. And the failure to sense a round fired is very rare which is a welcome change from using the optical sensor chronographs which failed to sense a round not infrequently. Therefore, from a consistency standpoint, the Magnetospeed seemed superior to optical sensor devices. However, there are drawbacks to the Magnetospeed. First, strapping the device on the end of a barrel will likely change the POI of the fired rounds. This means that zeroing or load testing and getting the muzzle velocity will always be a two step process. When the unit was first purchased it was hoped that the POI method of obtaining muzzle velocity could be employed simultaneously with measuring the same round using the Magnetospeed. That idea was put to rest shortly after a few rounds were fired with and without the device strapped to the barrel. Depending upon the rifle and the particular load being tested, sometimes the rounds printed high with the Magnetospeed, sometimes left or right, sometimes close to the zero, sometimes low. Most times the groups opened up; sometimes not. Suffice to say that it is not advisable to use the Magnetospeed while simultaneously trying to verify muzzle velocity via POI analysis. And since we cannot get a measured muzzle velocity for the same round that prints on the target to compare the two, we are back to using averages: the average MagnetoSpeed velocity results compared to the average velocity as disclosed by the group shot at range.
     The second drawback is that the Magnetospeed is, of course, limited to obtaining a muzzle velocity. To the extent that a shooter wants a downrange bullet velocity to compute ballistic coefficients, the MagnetoSpeed will be of no help and we are back to using 1) the traditional chronographs or 2) some sort of acoustic measuring device for time of flight analysis or 3) Doppler radar. The traditional chronographs like the CED, Oehler 35P, PMV-21, can be used out to 300 or possibly 400 yards/meters (500 if you don't mind putting your device at risk) and I've seen acoustic devices (along with the ability to POI data) usable at 1000 meters, but these latter devices are very expensive. And Doppler radar data is the most expensive of all, but the absolute best data available. So the Magnetospeed has limited application.
     The third drawback is the method used to strap the device to the rifle barrel. Sometimes the strap loosens during a firing sequence and when that happens, the reported velocities become erratic. Sometimes the straps stay taut but the device works its way forward under recoil which can only have a negative impact on velocity measurement. The problems associated with affixing the device to the rifle barrel was a consistent source of annoyance. In fairness, however, these problems may have been addressed to one degree or another in subsequent versions of this product. We tested only V1 but didn't feel it a good worthwhile expenditure to upgrade since whatever improvements were made to barrel attachment issue would never solve the issue of a change in POI.


Labradar - This is a genuinely new approach to measuring muzzle velocity. Essentially this device is a miniature, low power Doppler radar unit that sits in close proximity to the firearm, picks up the bullet being fired, and begins tracking the velocity of the projectile downrange. It is easy to set up, can be used on the shooting bench next to the rifle, does not interfere with barrel, grouping, or point of impact.  It is generally unaffected by light or weather conditions and so avoids the issues of both the optical sensor units and the Magetospeed.  We are testing the unit at this time and have the following technical questions:

  1. How is V0 calculated?  We know that the unit is triggered (i.e., starts broadcasting its microwave beam) by the muzzle blast which means that the bullet is some distance downrange when the broadcast starts. Is this distance important?  It may be depending upon what the radar is measuring.  Generally, Doppler radar will interpret a signal that is bounced back from an object by first looking at the phase shift of the frequency of the signal.  That will disclose the speed of the object.  Second, if the unit can measure the time it took for an impulse to be reflected by the object, it can figure out how far the object is from the radar unit.  If, on the other hand, the unit is simply broadcasting a continuous wave signal, this timing information may not be available in which case the unit will have to calculate the distance by speed plus the distance covered by the object before the radar actually began to broadcast. 
  2. How does altering the place where the bullet enters the microwave beam affect calculated V0?  The unit comes with a small V notched into the top of the plastic housing that is to be used as an aiming point to insure that the radar unit is pointed directly at the target.  It is a crude alignment device, however, which means that the radar beam will not always be in the same place relative to the firearm from session to session.  Furthermore, the unit may need realignment during the shooting session which means that the beam location will change.  These changes to beam location clearly mean that the fired bullets will enter the beam at a different location downrange after adjustment.  Does this have an effect upon the V0 calculation?  Does changing where the beam is pointed change the calculation as to how far the muzzle is from the point the unit first intercepts the projectile?
  3. The user has the ability to specify up to five (5) downrange distances for the unit to obtain and report the bullet's velocity.  So, for example, the shooter may want to know what the velocity of the projectile is at 25 yards and specify V1 for that distance.  But where is V1 measured from?  Is V1 measured from a point 25 yards from where the bullet entered into the microwave beam?  Or is V1 supposed to represent a point 25 yards from the muzzle?  If the latter, then we get back to the questions posed in questions 1 and 2.

Unfortunately, the folks at Labradar will not provide answers to these questions.  When you call the Support telephone number, you will not be talking to a technician; you will be talking to a salesperson who cannot respond to technical questions.  Instead he will assert that this information is "proprietary."  It isn't.  These questions don't seek design or computation details; they seek basic information as to the type of Doppler radar configuration that has been used.  It is not secret, proprietary, or even confidential.  It is basic product information that should be readily available because the answers will enable a reasonably intelligent shooter to set up his system to obtain the most accurate data that the system can generate.  We are disappointed that this information was not forthcoming. 

Update:  23 Mar 16 - We spoke with an engineer at Infinition, Inc., the company that actually designed and manufactures the Labradar and received answers to the above questions.  Basically, this radar is a simple continuous wave radar that provides velocity data only derived from the Doppler shift in frequency of the returning microwave beam.  The actual range of the projectile at any point must be calculated as is the original muzzle velocity of the projectile.  These calculations are based upon essentially two values: the speed of the projectile at a point in space and the time the projectile took to get to that place.  The time is computed based upon the muzzle blast as the triggering event to start the timer.  This timing event has to be modified to take account of the speed of sound to get from the muzzle to the radar device and the computation of the muzzle velocity has to be computed and is based upon the time/distance values of the projectile.  Therefore, we believe that a user of this device would be best served to place the unit within 6 inches laterally from the muzzle of the firearm (or slightly behind the muzzle if the firearm has a muzzle brake.)  We will test the computed V0 values against the actual trajectory and see how well the muzzle velocity as derived from the actual point of impact on targets compare to the computed V0 values recorded by the Labradar.