Garmin Xero C1 Pro chronograph

[LRCampos]

Best I can tell, the Garmins do as good a job of measuring muzzle velocity as most anything. I believe they interpolate a MV from measuring in front of the muzzle because they can't measure right at the muzzle.

To investigate, I ran a 20 round test on an Oehler 35P with a 9' spacing. That gives velocity at the middle screen. I sandwiched the middle screen with a couple of Garmins.

I put the setup and data below.

I don't trust any chronograph for better than about .1% - 3 fps on a 3,000 fps shot. I think even that is optimistic. That is my one gripe with the Garmin, it reports to the 1/10 of a fps. I don't think it is that accurate so why not have the option to round to the nearest whole fps?

So, one could argue the point is "if the Garmin measures at it's location and they tell you to place it 5" - 15" behind the muzzle, how much velocity would be lost in that distance from the muzzle?

Personally, I don't think it matters.


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Nice test!
What was the distance the Oehler Cronograph was from the muzzle?
It is dificult to say from the picture, but it seems like around 6 feet (2 meters)?

 

[Secant]

 

[lash]

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Hmmm…interesting results. While not conclusive, that seems to imply that the Xero is measuring velocity somewhere beyond the muzzle and that mounting the Xero gives somewhat faster velocity results. Though some of that might be within the noise of testing and instrument accuracy.

 

[Buford Boone]

Nice test!
What was the distance the Oehler Cronograph was from the muzzle?
It is dificult to say from the picture, but it seems like around 6 feet (2 meters)?

Skyscreen chronographs measure velocity midway between the "start" and "stop" screens (no offense intended, you probably know this but there may be some readers that don't).

I think the start screen was 9.5 feet. I was using a 9 foot spacing so the point the Oehler was measuring velocity would have been 14 feet in front of the muzzle (that is also the location of the "proof" screen...the Oehler makes two velocity measurements on every shot).

The Oehler measured velocity at 14 feet and I had two Garmins at the same distance from the muzzle. Therefore, my conclusion is that the Garmin measures velocity somewhere in front of the unit and uses interpolation to calculate the velocity at the unit.

Since they recommend you place the unit between 5 and 15 inches behind the muzzle, the only question would be "How much velocity difference is there between muzzle and 5 - 15 inches behind the muzzle.

I call the reading "Muzzle Velocity" and go from there.

(edited to correct the distance at which the measurement was taken. 1/2 of 9 is 4 1/2. so, 9.5 plus 4.5 = 14. DUH!)

 

[Buford Boone]

Hmmm…interesting results. While not conclusive, that seems to imply that the Xero is measuring velocity somewhere beyond the muzzle and that mounting the Xero gives somewhat faster velocity results. Though some of that might be within the noise of testing and instrument accuracy.

I saw better agreement when running a Magnetospeed at the same time as a Garmin. Don't know what caused the disagreement in the photos.

That can happen with any instrument. It is the reason I run two whenever making important measurements. IF they are in good agreement, everything is probably good. If not, I've got a setup issue and I adjust to fix it.

I've heard mounting one on a rifle may influence the velocity reading due to backward movement of the rifle at ignition. I've not tested for it, though.

Good data, Secant.

 

[Glassaholic]

Appreciate the data points Buford and Secant...

@Secant - who's cover is that on the weapon mounted Garmin?

 

[Ichi]

Appreciate the data points Buford and Secant...

@Secant - who's cover is that on the weapon mounted Garmin?
View attachment 8632011

Gray Ops Inc.

https://grayopscnc.com/collections/shooting-gear/products/garmin-xero-bump-cover-1

 

[LRCampos]

Skyscreen chronographs measure velocity midway between the "start" and "stop" screens (no offense intended, you probably know this but there may be some readers that don't).

I think the start screen was 9.5 feet. I was using a 9 foot spacing so the point the Oehler was measuring velocity would have been 12.5 feet in front of the muzzle (that is also the location of the "proof" screen...the Oehler makes two velocity measurements on every shot).

The Oehler measured velocity at 12.5 feet and I had two Garmins at the same distance from the muzzle. Therefore, my conclusion is that the Garmin measures velocity somewhere in front of the unit and uses interpolation to calculate the velocity at the unit.

Since they recommend you place the unit between 5 and 15 inches behind the muzzle, the only question would be "How much velocity difference is there between muzzle and 5 - 15 inches behind the muzzle.

I call the reading "Muzzle Velocity" and go from there.

Thank you for your explanation!

I will do the same: will read my Garmin measures as "muzzle velocity".