Data truing (Drops/BC) with Kestrel

[Mauser06]

Trying to true my data in my Kestrel.


It was spot on till I got to 800yds. 700-800-900-1000 were all hitting lower than the Kestrel called for.


Velocity verified via Labradar.

130gr Hybrid at 2880.


G7 BC on the box and AB library is .287.



To get my data to line up with what I had to dial, I have to change ge the BC to .268. Looking at the numbers, changing the BC doesn't change much until you get beyond 500.

I am new to this stuff...


I will verify this week....but wanted to make sure I'm on the right track. I don't know "how much" to play with BC numbers vs velocity etc. I've ran a bunch of that load through the lab and thats a pretty solid average.


Any thoughts?

 

[Mauser06]

Ha....interesting enough....if I use GeoBallistics with the factory bullet data, it lines up nearly perfectly at 1k.

Will have to play around at the range and see what the deal is. I was shooting a club match and not taking notes like I should have been....with components being tough to come by, I figured I'd do my long range testing at the club match and figure it out as I go.

 

[eric32]

True velocity at 600 yards and BC at 800 yards.

Remember your rifle is a system with the bullets is shoots. There can be so many factors of degraded BC. Rifling characteristics, velocity, altitude.

I double check your rifle inputs bore height, zero distance.

 

[eric32]

Also this might help as well

Ballistics Archives

Sniper's Hide has advanced discussions on using a ballistic calculators. Ballistic solvers can be an excellent tool for the long range shooter.

www.snipershide.com

Weaponized math

 

[NZ_Fclass]

I have yet to get my trajectories to agree to software past 600. I note where the load/rifle/scope shoots at each range (club) and use that record. I guess that's one reason we get sighters.

 

[eric32]

Then you need to take a look at your software inputs. Your BC needs to be adjusted or your scope tracks either high or low.

 

[Mauser06]

Thanx Eric. That was a good link. I'm a member over there...but haven't surfed around and found resources like that. And some days, I just can't stomach to post anything there knowing what I will have to sort through to get some good advice.


My downfall last time was not writing down my data. I was too "caught up in the match" and talking to the buddies. I know my 1k dope...only because I purposely left it on the scope.

It was 700 or 800 it was lower than the Kestrel. My buddy said the same thing you did. True BC at 800 or 1k and true velocity at 500 or 600...but he was shooting in a squad that started later so I wasn't able to dive deeper than that.

Inside 700 or 800 it was dial up what the kestrel spit out and make a good shot and it was an impact.


Like I said, I have data lining up at 1k. I just don't know "how much" it's normal to true BC...or if my numbers are excess, that point towards something else being astray.



I will see what it does Thursday. And I will take notes the entire way out like I should have been doing.

Have 6-8 weeks left of the league. Thatll really about do it for the season so trying to make the most of it. So far, I'm enjoying the long range stuff. I think tactical/practical steel shooting is definitely my game.

 

[eric32]

Also I recommend the CDM if possible and sign up for the kestrel virtual seminars

 

[FeMan]

As Eric said, true velocity out to 600 and after that, use drops to dial in your bc. The farther out you do it the better. That is, as long as you stay supersonic. Once you get to transonic the bc starts to climb and once you get to subsonic, it drops. There are all kinds of things that affect bc. AB is a good place to start but your bullet lot will be different and your weapon system will affect it too.

 

[STOMP442]

With todays technology you should have a hard velocity number within a couple fps. You shouldn't have to true velocity at all at any given range. BC, maybe, but also with todays measuring capabilities should be very very close especially if you are using a Litz measured BC value and not an advertised one which it looks like you are. I would double check your sight height and also do a tall target test to verify the that your scope is actually moving the correct amount. There have been a couple instances where I have had trouble getting the outputs of a calculator to match actual results in the field. A tall target test fixed that and an adjustment in the elevation correction factor field yielded much better results at all ranges.

 

[CharlieNC]

Several times I have read the guidance to true velocity at 600 and BC beyond., but I have never seen the source showing the logic and ballistics behind this. Interesting, anyone have a good reference?

 

[eric32]

That depends on what your using is it G1/G7 or a CDM.

But the official answer is a blend of 85% of transonic range from kestrel using a CDM.

If you don't have access to a CDM you can manipulate REAL WORLD PROVEN data and line that up with your kestrel. Usually between 500 to 700 yards velocity makes the most changes in output data.

After 800 BC seems to take over.

You can do an experiment your self and see what conclusion you come up with

 

[eric32]

So these numbers are here to get the rifle system and kestrel to match input for output.

While you might get an accurate MV from a magnetospeed or lab radar. Don't get married to this number. Remember the gun doesn't lie it tells you the truth.

By truing we are giving the kestrel what is wants to hear to give us the number that line up with reality.