Episode 71 Kestrel Lesson

[SFeldt]

So I had an opportunity to get out and true my kestrel up as suggested in this episode and had some unexpected results. I have previously been running the custom drags and have experienced some issues. I'm running a RPR with a 26inch bartlein 1-8 RH twist in 6.5 creed a nightforce atacr 7-35 that tracks 99%. My load is Berger 130 AR Hybrid OTM Tactical (G7 of .287 on the box) at 2997 fps 20 shot avg. I confirmed my zero and did the hornady true range method. Frank suggested 800 yards to true BC so I went out to 784 yards measured from my turrets with 2 rangefinders. Kestrel told me 16.13 MOA with WS1 at 0 so I put on 16 MOA hit low for 3 rounds. I put on 16.25 MOA hits were impacting just under my hold for 5 rounds. Went to a diamond to confirm for another 10 rounds average just low of hold. I started to mess with the BC to my surprise I had to lower my bc .280 that made the kestrel tell me 16.32. Kind of unexpected to have to lower my bc at almost 3000 fps. Did I do something wrong maybe?? Lowlight

My environment
Temp-72°
SP- 29.05
RH-80%
DALT-2150
ALT-863
LAT-42°
TARGET-353°
WIND 1:30 AT 7-10 MPH

 

[SFeldt]

So I had an opportunity to get out and true my kestrel up as suggested in this episode and had some unexpected results. I have previously been running the custom drags and have experienced some issues. I'm running a RPR with a 26inch bartlein 1-8 RH twist in 6.5 creed a nightforce atacr 7-35 that tracks 99%. My load is Berger 130 AR Hybrid OTM Tactical (G7 of .287 on the box) at 2997 fps 20 shot avg. I confirmed my zero and did the hornady true range method. Frank suggested 800 yards to true BC so I went out to 784 yards measured from my turrets with 2 rangefinders. Kestrel told me 16.13 MOA with WS1 at 0 so I put on 16 MOA hit low for 3 rounds. I put on 16.25 MOA hits were impacting just under my hold for 5 rounds. Went to a diamond to confirm for another 10 rounds average just low of hold. I started to mess with the BC to my surprise I had to lower my bc .280 that made the kestrel tell me 16.32. Kind of unexpected to have to lower my bc at almost 3000 fps. Did I do something wrong maybe?? @Lowlight

My environment
Temp-72°
SP- 29.05
RH-80%
DALT-2150
ALT-863
LAT-42°
TARGET-353°
WIND 1:30 AT 7-10 MPH

 

[SFeldt]

@Lowlight

 

[Lowlight]

It is what it is, the velocity factor is just one part of the puzzle, granted a big part, but Believe the bullet

if the results are, a better solution, read, more accurate solution, then it worked,

Did you start with an actual MV or did you use the adjusted MV from prior ?

 

[SFeldt]

We didnt have a chance to shot the 1100 yards for a muzzle velocity cal. because of the corn being to tall we should of mowed it down with a combine man lol??...but I did shoot the 20 round average over a magnetospeed v3 and a labrador both were within 1fps of each other. It does result in a better solution. So in the end I'm good. I just kinda expected to increase the bc because of that speed.

 

[Lowlight]

It's always a high velocity is up and lower is down, it's how the rifle performs,

The velocity on my 20" 1-7 is a bit down, but the BC is up because the super fast spin keeps it pointed straight so the bullet flies a touch better at distance.

There are several variables at play and they add to the mix.

The better solution means the job well done!

 

[Long Range 338]

The velocity on my 20" 1-7 is a bit down, but the BC is up because the super fast spin keeps it pointed straight so the bullet flies a touch better at distance.

Ok @Lowlight, I think my head just exploded.... This sounds like some Sherlock Holmes level stuff. If I was shooting low, I would drop BC first or velocity at some point to build the drag curve. So specifically:
-How do you arrive at lower velocity and then higher BC to get it right?
-I assume it was the twist rate that started you down that path?
-Would this scenario ever happen with a standard twist rate?

I've got a couple of rifles I've been trying to true and just can't seem to nail all the variables to get it just right. It's always close but not right on.

 

[Lowlight]

Tuning the BC is a bit of Trial and Error,

It's partly the twist because I run the Gain Twist stuff, but it's also the distances we are shooting. We shoot farther so the fine-tuned BC helps balance the longer distances, but it's more than that, it's the WIND.

The BC controls the wind value and if you notice the Apps are never right when it comes to wind. Tuning the BC helps with the wind, and because we are using the G1 Wind Model we find it helps to tune the wind better to adjust it.

My range goes every 100 yards to a 1 Mile and we can back up pretty far. So we are not testing this stuff at shorter ranges and modeling it. We are truing at distance and adjusting the BC to match. This is combined with the better Chronographs we are using> If a guy goes out and buys a $500 Labradar and then changes his MV, 50fps, 100fps, or more, what is the point of buying a Chrony?

The manufacturer BC is a starting point, you want to tune it for your Rifle System. Unfortunately, it's a bit of trial and error, no getting away from that. I don't have a formula or rule of thumb, only knowing:

My drop is less than predicted, increase the BC, if my drop is more than expected decrease the BC.

I did it yesterday, drop at 800 was 4.9, calculator said, use 5.2, so the BC comes up until the number matches. Almost the entire prediction is gonna be off by .3 after 800, so changing the BC moves that needle but leaves my 400 yard dope alone.

 

[Kobyashi72]

So I had an opportunity to get out and true my kestrel up as suggested in this episode and had some unexpected results. I have previously been running the custom drags and have experienced some issues. I'm running a RPR with a 26inch bartlein 1-8 RH twist in 6.5 creed a nightforce atacr 7-35 that tracks 99%. My load is Berger 130 AR Hybrid OTM Tactical (G7 of .287 on the box) at 2997 fps 20 shot avg. I confirmed my zero and did the hornady true range method. Frank suggested 800 yards to true BC so I went out to 784 yards measured from my turrets with 2 rangefinders. Kestrel told me 16.13 MOA with WS1 at 0 so I put on 16 MOA hit low for 3 rounds. I put on 16.25 MOA hits were impacting just under my hold for 5 rounds. Went to a diamond to confirm for another 10 rounds average just low of hold. I started to mess with the BC to my surprise I had to lower my bc .280 that made the kestrel tell me 16.32. Kind of unexpected to have to lower my bc at almost 3000 fps. Did I do something wrong maybe?? Lowlight

My environment
Temp-72°
SP- 29.05
RH-80%
DALT-2150
ALT-863
LAT-42°
TARGET-353°
WIND 1:30 AT 7-10 MPH

Out of curiosity do you have the following info available?



Sight height?



(Wind info)

Did you zero your rifle in the 7-10 mph wind?

Is the position you zeroed at blocked from the wind?

Was there 7-10 mph blowing when you shot at 784?



(Zero)

What was your zero distance?

What was your “true” zero range?

 

[Hardpan]

Tuning the BC is a bit of Trial and Error,

It's partly the twist because I run the Gain Twist stuff, but it's also the distances we are shooting. We shoot farther so the fine-tuned BC helps balance the longer distances, but it's more than that, it's the WIND.

The BC controls the wind value and if you notice the Apps are never right when it comes to wind. Tuning the BC helps with the wind, and because we are using the G1 Wind Model we find it helps to tune the wind better to adjust it.

My range goes every 100 yards to a 1 Mile and we can back up pretty far. So we are not testing this stuff at shorter ranges and modeling it. We are truing at distance and adjusting the BC to match. This is combined with the better Chronographs we are using> If a guy goes out and buys a $500 Labradar and then changes his MV, 50fps, 100fps, or more, what is the point of buying a Chrony?

The manufacturer BC is a starting point, you want to tune it for your Rifle System. Unfortunately, it's a bit of trial and error, no getting away from that. I don't have a formula or rule of thumb, only knowing:

My drop is less than predicted, increase the BC, if my drop is more than expected decrease the BC.

I did it yesterday, drop at 800 was 4.9, calculator said, use 5.2, so the BC comes up until the number matches. Almost the entire prediction is gonna be off by .3 after 800, so changing the BC moves that needle but leaves my 400 yard dope alone.

Thanks to you and Mike for the excellent Kestrel podcast. I just received a 5700 elite and the guidance from the podcast really helped me dial it in. I am slowly messing with the BC to correlate to the data I have in my log book at the different ranges with different factory ammo. Thanks again for the knowledge drop!