Does the MagnetoSpeed V3 chronograph change group size and point of impact?

Does the MagnetoSpeed V3 chronograph change group size and point of impact?

For many of us the MagnetoSpeed barrel mounted ballistic chronograph has been a game changer.  As a guy who used to drag his Oelher 35 P chronograph, sky screens and printer to the range and spend a good deal of time setting it up, the MagnetoSpeed has been a huge help in saving time and encouraging a greater degree of data collection.

Precise, forgiving to use and ends the frustration often associated with the sky screen type chronographs.  No more long set ups, chasing the right light or missed shots.  The MagnetoSpeed just works.  You can find the results of my testing here.  Note: The LabRadar, which doesn’t attach to the rifle should work even better; however, I have been unable to reliably collect data with mine.

The upside of the system is also its downside, it attaches to the rifle’s barrel.  If you aren’t paying attention you can shoot the sensor off of the end (don’t ask me how I know) and, in theory could possibly affect your point-of-impact and group size.  Anecdotally, I’ve found my heavy barrel rifles tend to shoot slightly higher with the MagnetoSpeed in place.  My thinner barrel hunting rifles don’t group particularly well with it in place, while my heavy barrel rifles do.  Since I’m always using the MagnetoSpeed V3 for testing and evaluation purposes, I thought it would be a good idea to conduct a quick test of how it may influence group size and potentially shot point-of-impact.

I grabbed 40 rounds of Gorilla 6.5 Creedmoor ammunition loaded with the 142 gr. SMK and my trusty 6.5 Creedmoor rifle and headed to the range.

This is my trusty test rifle, built with parts from Brownells, it is made up of the following:

All the parts; the barrel, chassis, scope and trigger, work well together for a nice shooting rifle!

It started in an AI AX chassis and then switched over to an MDT ESS.  I’ve been shooting the ESS a lot lately and have grown quite fond of it! (Click here to learn more about the ESS)

My plan was simple.  I’d fire four 5-shot groups prone from a bipod with a rear bag using the MagnetoSpeed, remove the chronograph and fire another four groups.  I’d be looking for  how much the point-of-impact changes (if at all) and also compare the group sizes.  Keep in mind, this is a limited sample size, but still should give an indication of what changes you might experience under similar conditions.

The results are shown in the target below:

The rifle was zeroed for my 107 TMK load.  In this case, the point-of-impact of the Gorilla 142 SMK ammunition was to the right of the target.  The top row of targets are the groups fired with the MangetoSpeed V3 in place.  The middle row was fired with the MagnetoSpeed barrel-mounted ballistic chronograph removed.  Note the point-of-impact seems to be higher with the MagnetoSpeed in place.

NOTE: If you are a regular reader you’ll note that my target looks different.  I used to use 1″ orange dots on cardboard targets.  They worked in most conditions, however, in heavy rain or extreme cold, the adhesive would fail and they would fall off the target (see the orange dots in the target above).  I developed this target with Rite in the Rain.  It is on waterproof stock with true 1.047 MOA green dots.  The color provides excellent contrast and you can still see your impacts on the paper.   Rite in the Rain sells these targets as well as paper that you can print your own targets on.   To learn more about Rite in the Rain and their line of targets, click here.

The average group size for the groups shot with the MagnetoSpeed in place (.560″/.535MOA) were also slightly smaller than those with it removed (.784″/.748 MOA).

Granted this was a limited data set but I believe it helps illustrate how the MagnetoSpeed may influence your data set.  Perhaps the easiest way to avoid this would be to load two batches of ammunition, one to shoot for muzzle velocity data, and the other to shot for group size.

I also want to take a minute to point out how well that Gorilla Ammunition shot!  For the 20 rounds I fired with the chronograph, I had a velocity of 2,570 feet/second with a standard deviation of 11.7.  That is great for factory ammo!  Check out the group below, that’s five shots at 100 yards folks!