Thanks in advance for your help gentlemen.
While gathering field data I discovered I have a bad chrony, or am using jbm or my kestrel wrong because the data for an 815 yard shot is 3 moa off.
The rifle: Rem 5r, 308win, Leupy mk4 that i have tested to track true in moa with a 100 yard zero.
The load: 175smk, FGMM brass, 45.0 Varget, CCI BR2. Chrony says 10 shot string averages 2615 with decent ES and SD.
Kestrel data:
Baro was 29.18. Reference altitude was zero so I believe this is a direct pressure measurement. (ie uncorrected)
Temp 93F
Humidity 40%
Wind less than 3mph, mostly headwind.
I KNOW my true field elevation is 900 ft.
Kestrel was saying the density altitude was about 3000ish.
With the above values the JBM data for the 815 yard shot with the Litz 175SMK selected, and the corrected pressure/std atmosphere boxes NOT checked, is 26.3 MOA. The problem is a box of ammo proved that I really needed only 23.25 MOA to repeatedly score good hits on the plate.
So the JBM calculation is off by a little over 3 MOA. So the question is why.
1. Is the chrony wrong? I was expecting about 2700 from this load.
2. Is the Kestrel data wrong? Kind of doubt this but you never know...
3. Is JBM inherently off that much? Seems quite a bit off and I think others are getting much closer so there must be some bad input somewhere. The plate is 11 inches so 3 moa off at 815yards means a miss everytime.
By the way, I can get the data to within about 1 moa of reality by increasing the velocity 100 fps to 2715 and using the supposedly less accurate most optimistic plain 175smk (non-Litz) model from the jbm bullet library. So that makes me lean towards a consistently slow chrony measurement, but that seems fishy since it is very consistently measuring slow everytime. Also, i trust that the Litz models for the 175smk are probably better.
All I know for sure is that unless someone changed gravity without telling me, that for some reason the jbm data is calling for way to much elevation. I want to find out why and fix it so I can build some laminated density altitude cards. Thanks again to anyone who can point out where I am going wrong!
While gathering field data I discovered I have a bad chrony, or am using jbm or my kestrel wrong because the data for an 815 yard shot is 3 moa off.
The rifle: Rem 5r, 308win, Leupy mk4 that i have tested to track true in moa with a 100 yard zero.
The load: 175smk, FGMM brass, 45.0 Varget, CCI BR2. Chrony says 10 shot string averages 2615 with decent ES and SD.
Kestrel data:
Baro was 29.18. Reference altitude was zero so I believe this is a direct pressure measurement. (ie uncorrected)
Temp 93F
Humidity 40%
Wind less than 3mph, mostly headwind.
I KNOW my true field elevation is 900 ft.
Kestrel was saying the density altitude was about 3000ish.
With the above values the JBM data for the 815 yard shot with the Litz 175SMK selected, and the corrected pressure/std atmosphere boxes NOT checked, is 26.3 MOA. The problem is a box of ammo proved that I really needed only 23.25 MOA to repeatedly score good hits on the plate.
So the JBM calculation is off by a little over 3 MOA. So the question is why.
1. Is the chrony wrong? I was expecting about 2700 from this load.
2. Is the Kestrel data wrong? Kind of doubt this but you never know...
3. Is JBM inherently off that much? Seems quite a bit off and I think others are getting much closer so there must be some bad input somewhere. The plate is 11 inches so 3 moa off at 815yards means a miss everytime.
By the way, I can get the data to within about 1 moa of reality by increasing the velocity 100 fps to 2715 and using the supposedly less accurate most optimistic plain 175smk (non-Litz) model from the jbm bullet library. So that makes me lean towards a consistently slow chrony measurement, but that seems fishy since it is very consistently measuring slow everytime. Also, i trust that the Litz models for the 175smk are probably better.
All I know for sure is that unless someone changed gravity without telling me, that for some reason the jbm data is calling for way to much elevation. I want to find out why and fix it so I can build some laminated density altitude cards. Thanks again to anyone who can point out where I am going wrong!
