TLDR Version: This is one installment of several experiments I'm doing with various chronograph models, specifically testing the difference in velocity readings when mounting the chronographs to the rifle vs. mounting on a static fixture beside the gun, such as the supplied tripods. The expectation was that the gun mounted chronograph would read higher velocity since the unit itself is moving rearward in recoil with the rifle compared to the static mounted chronograph. This experiment confirms that expectation - the gun mounted chronographs read an average of 3.5fps faster than the static chronographs beside the rifle.
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As part of a large series of chronograph comparisons, I conducted last week a test to determine the influence of mounting doppler radar chronographs to the rifle vs. to static mounts beside the rifle, like the supplied tripods.
Experiment Overview: Gun Mount vs. Static (Tripod) Velocity Readings:
In speaking about this series of experiments with shooters around the web, many folks have mentioned that they expect to see higher velocity readings when mounting mini-doppler radar chronographs to a rifle than when using the chronograph on the supplied tripod beside the rifle, due to the fact the gun mounted chronograph is moving rearward during recoil compared to being fixed to the Earth on a static mount. To test this hypothesis, I mounted 3 chronographs to the rifle with matching units mounted on a static rack beside the rifle, and fired 30 rounds. I then swapped the units from rack to rifle and rifle to rack to allow identification of unit-to-unit offset vs. dynamic vs. static mount influence. This experiment was intended to capture and demonstrate this potential offset in speed read by gun mounted vs. static mounted units.
Aspects of Comparison:
The rifle used for this test was a Defiance Deviant Elite Short Action, Bartlein barrel 26" 1:7.5" twist chambered in 6 Dasher with SilencerCo Omega, firing handloaded ammunition:
Berger 105 Hybrid 6mm
Hydroformed Lapua 6 BR brass --> 6 Dasher (>15 firings)
30.5gr Varget
CCI BR4 Small Rifle Benchrest Primer
This comparison was made using the same 6 chronographs of 3 models:
- Garmin Xero C1 (x2 - noting, one of the Garmins used in this test is NOT the same unit as used in previous testing)
- LabRadar LX (x2)*
- Athlon Rangecraft Velocity Pro (x2)
*Unfortunately, time constraints on the day of testing and shot registry errors made the LabRadar data sets incomplete to the point of failing utility for this comparison. Additional replication of the experiment may be conducted.
As shown in other threads around the web, I built this holding fixture to allow multiple chronographs to be mounted within the specified distances from the bore and concurrently fired to limit the burden of ammunition volume required to conduct these experiments, and to allow comparison of brand behavior reflecting the exact same experimental substrate (same exact shots).
For this experiment, I partially disassembled this holding fixture and only used one upright stanchion, holding 3 chronographs, and then mounted the opposing 3 chronographs to 2 ARCA rails mounted to my rifle:
Results of Comparison:
For ease of visualization, I applied a heat map to the data captured from the 2 units of each brand, and compared the velocity readings for 30 rounds (less read failures). In the majority of readings, the gun-mounted unit detected higher velocity than the static mounted unit. Green means that unit read the faster speed between the two, red means that unit read the slower speed between the two for each respective shot. We can see that a few shots do flip flop, but the overwhelming majority of shots show the faster speed read by the gun mounted chronograph of each brand.
The Garmin mounted to the rifle during the first string produced readings which averaged 4.5fps faster than the Garmin mounted on the static rack, and exhibited the faster speed 20 out of 27 readings. The Athlon mounted to the rifle read the higher velocity than the static-mounted Athlon in 20 of the 30 readings, and averaged 2.4fps faster than the Athlon on the static rack.
To evaluate whether the offset observed between the two units was caused by the mounting position rather than caused by inherent offset between the units (meaning maybe one unit always reads faster or slower than the other, no matter where it would be mounted), the units were swapped from the static mount to the gun and vice versa, and the same results persisted - the gun mounted units registered faster speeds for the majority of shots than the unit mounted on the static rack. Swapping the position of the units, the velocity offset also swapped. The Gun Mounted units again displayed the faster velocity than the static mounted units from each brand, again visibly represented here by the red/green heat map. For each, individual shot, the faster reading between each brand (green) was registered by the gun-mounted unit, faster than the static mounted unit.
In the second series, the Gun Mounted Garmin registered the faster speed than the Static mounted Garmin for 27 of the 30 shots, averaging 3.3fps faster. In 22 of the 30 shots (one tie), the Gun Mounted Athlon unit registered the faster speed than the Static Mounted Athlon, averaging 3.9fps faster than the static unit.
Across both series, the gun mounted Garmin recorded the higher velocity in 47 of the 57 shots fired, and the gun mounted Athlon recorded the higher velocity over the static mounted unit in 42 of the 60 shots they recorded. The average offset for all shots was 3.5fps faster reading on the gun mounted units than the static fixture units.
Further visualizing these trends by plotting the velocity readings for each unit, we can see the faster trend for the gun mounted unit over the static mounted unit, and can see the swap in the trend for each unit when they are swapped between the rifle mount and static mount.
Depicted here are the trends for each Garmin unit - Garmin 1 started the experiment on the static rack with Garmin 2 on the rifle (actually Garmin 3); during this phase, Garmin 2 read the faster speed as mounted on the rifle than Garmin 1, which was mounted on the rack. When swapping Garmin 1 onto the rifle and Garmin 2 (3) onto the rack, the trends swapped and the gun mounted unit again rose to the top of the trends.
This was also observed for the Athlon units. Athlon 1 was mounted to the rifle for the first half of this test, depicted in the dark green line, which carried (predominantly) above the static mounted Athlon 2. When swapping the two units, moving Athlon 2 to the gun and Athlon 1 to the static mount, the Athlon 2 shifted to the higher velocity over Athlon 1, trading the teal line above the dark green line.
Conclusions and Considerations of Comparison:
One conclusion I'm drawing for myself out of this experiment is that I should repeat the this with a few modifications which I believe will 1) improve the data integrity by establishing a standard offset, a normalization factor, between each of the units before introducing the mount variable, 2) corroborate and supplement findings from this test, and 3) successfully execute the experiment with the LabRadar LX's. I was pressed for time during this test, and wasted a lot of time fighting with the LX's, so I eventually just gave up - I missed shots with one of the LX's on nearly half of the shots, which made it impossible to determine during analysis which shot records from one really lined up with the records from the other unit, so I trashed the data.
I also recognize that I changed one of the Garmins I was using in this test compared to previous experiments, and I do not yet have a normalization factor, a standard offset, for the new Garmin vs. my other Garmin. In other experiments, I identified that my two previous Garmins averaged only 0.54fps difference for any given shot, and never exceeded more than 2.4fps difference for any shot in a test including over 100 rounds, so I could be more confident that the 3.5fps average offset is normalized across the units - but because I used a new, 3rd Garmin, I can't be sure the same 0.54fps average applies, and need to establish a new normalization factor. Repeating this experiment, I will include a 3rd phase in which I will shoot 25-30 rounds with the units both in static mounts to allow determination of the standard offset factor, then repeat the 25-30 round test with one gun mounted and one static mounted, and again swap for a final, 3rd phase of another 25-30 rounds with the units swapped from gun to rack, rack to gun.
Considering the specific results for this experimentation, I consider the hypothesis to be confirmed that gun-mounting mini doppler radar chronographs will produce higher velocity readings than using the chronographs mounted on their supplied tripods or other static mounts. The offset for this load and rifle was 3.5fps faster reading for the gun mounted unit over the static unit. This, of course, reflects the specific recoil velocity of my cartridge/load and rifle used for this experiment.
