Precision Rifle Gear Garmin Xero reading high

[Metzger]

I picked up a Garmin March 8th and had it out in the field March 12. No problem, reading the right speed with rifle A. I take it out today March 16th, it reading high with four different rifles like 25fps with 22lr, 50fps with 17hmr and 100 FPS with centerfire. Any ideas?

 

[Jefe's Dope]

How are you confirming it's reading high?

 

[vh20]

How are you confirming it's reading high?

This.

 

[Slides]

That sounds like normal rifle variance if it's just difference to factory ammo spec.

 

[Jcarpenter223]

How are you confirming it's reading high?

I'm curious as well. Looking to nab one here pretty soon

 

[MO Fugga]

Environmental changes over the days?

 

[MO Fugga]

I'm curious as well. Looking to nab one here pretty soon

Get it from Brownells. That return policy is awesome.

 

[rmfield]

Mine consistently runs about 0.1% to 0.2% low compared to my Magneto Speed when tested at velocities from about 1050 - 2950 FPS. No idea which one is "right", but the variance remarkably low.

 

[Metzger]

I'm curious as well. Looking to nab one here pretty soon

We had caldwell and a magneto speed on site with a 1000 yards to verify.

 

[vh20]

100fps higher reading than a Magnetospeed would certainly indicate an issue with one or the other. The 1000 yard impacts would verify which one (which it sounds like you must have). Time to call Garmin if that’s the case because that’s way out of spec.

 

[Jcarpenter223]

100fps higher reading than a Magnetospeed would certainly indicate an issue with one or the other. The 1000 yard impacts would verify which one (which it sounds like you must have). Time to call Garmin if that’s the case because that’s way out of spec.

This. Chrono data is just an idea for me, then I'll verify at distance

 

[Islas82]

I know two guys I shoot with having similar issues. I believe their variances are around 60-90fps 4 or 5 shots in a string of 10. I consider both of them to be good methodical reloaders.

I have noticed some variance of 60-70fps but only 1-2 shots of a 10 shot string and usually it’s my first 10 shots of the day so thats not enough for me to call it an issue with the unit.

 

[diggler1833]

I know you spent the money and want 100% accuracy. However I'd verify the reading with a centerfire group at 6-700 just to see how much (if any) correction was needed. If you're ~ .3 - .4 of a mil off at that range, then you definitely have a 100 FPS reading error. May be a touch more or less depending on cartridge, but anything more than two tenths deserves a little investigation.

I don't ever trust chronographs completely, but they should get you close. My two current cheapos are good for getting me within 30 FPS of trued velocity after I run it at 600 - 650.

Definitely interested in the Garmin myself, so keeping an eye on this thread.

 

[308pirate]

Call me suspicious of amateurs calling into question a measurement instrument's accuracy and precision.

 

[375fan]

This. Chrono data is just an idea for me, then I'll verify at distance

Distance tells the truth.

 

[diggler1833]

The problem with trying to true your MV at distance is the other variables that can be involved. Not all barrels produce the same BC in a bullet. And bullets have a BC ES and SD as well. If you shoot 20rds onto a 1000yd F Open target I'd take that data as gospel but the ol' 1 to 2 rds in a piece of steel doesn't produce enough statistically significant data. And the biggest variable is the the shooter's ability to maintain a zero. I've seen plenty of guys try to true at distance and F it up. And if you're witness statement is written by a Caldwell color me double-dubious

I believe it difficult to argue with gravity.

5 round groups at minimum, 6-700 for MV, 900-1K again for BC. Works pretty well. If you can't keep a zero at 600, then you can't at 100 either.

Although more than one guy has his own methods of verification, so I'm sure that others exist. I've also found that my single digit SDs translate into .3 MOA/.1mil or less vertical at 6-700.

I find it rare that dudes who are into gathering and truing data points like this are into shooting single rounds for verification. But I know the exceptions exist.

I agree that Caldwell is not to be taken as gospel.