Kestrel Help - Incorrect output

[EXSOCAL]

I’ve owned an ABM Kestrel now for a while and have noticed a couple issues recently. I got a target load dialed in for my 7mm RSAUM and got a good 15 shot average velocity. I input all the data into the kestrel link ballistic program and sent it to the device. Fast forward to the range today.... I confirmed zero at 100 and shot a nice group. I pasted a target at 300 and dialed my elevation based on the kestrel... it called for .63 mils. My subsequent group of 5 was right at .2 mils low. Made the adjustment to .8 mils total and had good 1” group centered up on the bull. Wondering what caused the Kestrel to be off, I re confirmed all my inputs. Everything spot on. I pulled out my phone and put the same inputs into the JBM calculator online and it somehow gave me the correct output of .8 mils at 300. I had this problem with a .243 old I shot in the past and ended up saying screw it to the kestrel and just used the JBM dope which was dead nuts.

I messed around with the BC and muzzle velocity in the Kestrel to try and true the data. In order to make it line up with what I was actually seeing I had to make some pretty drastic changes to both the BC and the MV. This didn’t seem right to me. I’m lost. Any advice?

I don’t have a range readily accessible to shoot past 800 yards to doing the whole transonic ballistic truing routine. But I am thinking it’s .2 Off at 300 then it’s gonna be way off at distance.

 

[djarecke]

You won’t see an effect by playing with BC at 300 yards. Leave that alone at close ranges. Here are my thoughts:

Is your range really 300 yards?

Was there a strong wind from nine o’ clock?

Did you drive the rifle by loading the bipod consistently?

Is your MV correct?

I’d try to get out to a longer range to verify if at all possible.

 

[_Windrider_]

Yeah these are really hard to help with unless you give us the complete data required to recreate your rifle profile as well as zero conditions and conditions during firing.

 

[EXSOCAL]

The range is 300 yards on the dot. Muzzle velocity was confirmed with my trusted magneto speed and double checked with another. I had 11-13 mph winds from my 2:00. Rifle was shot off an atlas and rear sand bag, I shoot a few hundred rounds a week for work and play and use the same bipod shooting technique each time.

As I mentioned before, I had this same issue with a .243 win shooting 107 gr sierras, the dope was off at 300, 500 and 1k. Same deal.

Specs on th rifle and environment from this morn:
7mm RSAUM
64 gr H1000 / Nosler Brass / CCI BR2 / 160 Gr Sierra TMK at .020 Off

Consistent sub .3” at 100 yards
2970 FPS with SD of 4.6 for 15 shots
Bighorn TL2 SA with a 26” bartlein 9 twist

Vortex Razor HD AMG 6-24

Enviro:

69 degrees
11-13 mph wind from 2:00
1,231 D Alt
42% humidity

I’ll be able to stretch is out later this month but I can guarantee it will be off at distance as well.

Scope is 2.85” over center of bore. Chrono distance is 2” (magnetospeed).

Everything in this is tried and true. There are no new unproven variables. I’ve shot this rifle out to a mile with great results, just using DOPE I gathered in the field.

What irks me is the JBM output is correct and th kestrel is not.

 

[_Windrider_]

I sent you a Pm. I’ll mess around with this. I have the desktop AB so sometimes that’s easier to spot the issue with AB.

 

[EXSOCAL]

Much appreciated!

 

[ophious]

This is what I came up with.

 

[_Windrider_]

DOf and what is your latitude? Want to see if coriolis is the issue.

 

[ophious]

Have you tried re-torqueing your rail and rings? I've seen that create major inconsistencies. Just out of curiosity, when you were having this problem before, were you utilizing the same scope?

 

[EXSOCAL]

DOF was 51 degrees. My lat was 32.63eg.

 

[EXSOCAL]

Absolutely no issues with the rig or ammo. It’s a hammer at distance and probably the most consistent rifle I own. I’ve killed several deer with it out to 800 yards with 155 gr cutting edge bulllets.

 

[EXSOCAL]

It’s the fact that the Kestrel’s Output is off, and when I switch to my 300 win profile or 6.5 SLR profile, they are right on. I was thinking I had a setting fucked up somewhere but everything is set up the same for all my long guns.

 

[_Windrider_]

I don’t even see the 160 gr TMK in the AB library, did you have to manually add it?

Edit: FOUND IT

 

[ophious]

I get a come up of .8 with a 0 altitude factor. Maybe the density altitude is screwing it up?

 

[_Windrider_]

Here is the AB Analytics output with component breakdown (I had to guess what your station pressure was).

notice how AJ decreases your drop because we are dealing with a 3/4 value wind from the right which cause the bullet to hit high. here it is with the same wind from 10 oclock:

Now if we take out coriolis here is what you get:

ive said it a million times, you dont need spin drift or coriolis when using AB until you are dealing with transonic ranges. my recommendation.....turn it off. One of the key things you see is how AJ is added or subtracted to your elevation. i feel like JBM adds it no matter what, which would be incorrect.

 

[_Windrider_]

I get a come up of .8 with a 0 altitude factor. Maybe the density altitude is screwing it up?

That doesn’t matter to the kestrel. In the background it doesn’t use DA, it uses pressure temp and humidity.

 

[_Windrider_]

look at the result when i switch to meters:

makes me ask the question.......you measuring in meters or yards?

 

[EXSOCAL]

I got it all figured out... and feel very dumb. I swapped the AMG into my 7mm which had low mounts on it... previously I had a Kahles K624i on there with much a higher Spuhr mount. There is almost .9” difference between the two scope heights and I initially changed the input to read the correct scope height of 1.96” and must have forgotten to save the change because the old 2.85” was still in there. When I saw that I didn’t realize it was wrong at first because I made the scope swap a while back. Just goes to show that the inputs are so critical, I need to stop messing with this stuff after working 12’s and going on 4 hours of sleep....

Thank you for everyone’s help.

 

[Hiker12]

Hello SoCal and TacticalDillhole, I will not divert this conversation trying to learn myself through the conversation going on. Having similar issues with my kestrol. Question for TacticalDillhole, at what distance do we use coroilis feature is it 1000 yards and beyond thanks

 

[_Windrider_]

Hello SoCal and TacticalDillhole, I will not divert this conversation trying to learn myself through the conversation going on. Having similar issues with my kestrol. Question for TacticalDillhole, at what distance do we use coroilis feature is it 1000 yards and beyond thanks

If only you could turn it on like that. It’s either always on or always off. I leave it off and never turn it on. If I were shooting 3 miles with a 7-8 second time of flight I might use it but for the vast majority of us it’s just totally unnecessary.

You could turn it off and turn it on and compare the solutions for your benefit and you will notice an almost indiscriminate change.

 

[_Windrider_]

I got it all figured out... and feel very dumb. I swapped the AMG into my 7mm which had low mounts on it... previously I had a Kahles K624i on there with much a higher Spuhr mount. There is almost .9” difference between the two scope heights and I initially changed the input to read the correct scope height of 1.96” and must have forgotten to save the change because the old 2.85” was still in there. When I saw that I didn’t realize it was wrong at first because I made the scope swap a while back. Just goes to show that the inputs are so critical, I need to stop messing with this stuff after working 12’s and going on 4 hours of sleep....

Thank you for everyone’s help.

So I have to ask, how did JBM give you the correct hold with the wrong info?

 

[Hiker12]

If only you could turn it on like that. It’s either always on or always off. I leave it off and never turn it on. If I were shooting 3 miles with a 7-8 second time of flight I might use it but for the vast majority of us it’s just totally unnecessary.

You could turn it off and turn it on and compare the solutions for your benefit and you will notice an almost indiscriminate change.

Thanks for the info. Will try it for comparison. May contact you in the future if you dont mind. Thanks dude

 

[EXSOCAL]

Interesting... JBM gives me .8 Mil drop at 300 with the incorrect sight over bore (2.8”) and gives me .9 Mil drop with the Correct SOB measurement of 1.9”. Maybe a lucky coincidence? I’ll hopefully confirm out to 1400 in the next week or so and really get to the bottom of this.