Strelok Pro and "multi" BC's

[Centercut]

I have a question I'm not able to find out about in the help section or FAQs for Strelok Pro. Those that have it know there is a section where you can input multiple BCs for a specific pellet/rifle combination. When you do this, you enter a velocity and a BC, and if you have varying velocities and BCs, you can enter up to five. Here is the question I asked Igor Borisov, but it still doesn't answer the question or make sense, since with his answer I'd enter the muzzle velocity the same for differing BCs.

Q: When I determine BC, I shoot at the muzzle, and at various distances to get more than one BC. This is for air guns, so if I shoot at 28.5 yards, and muzzle is 882fps, and at 28.5 yards is 799fps which gives a BC of .0375, what number do I use in the app for velocity? 882 or 799? Same question for at 48.5 yards, do I use the 754fps?
Chart with data for BC calculations
Pellet 1.5y 28.5y BC 48.5y BC 
JSB 18.1 882 799 .0375 754 .0387

A: 882
Igor Borisov

See what I mean? Or am I missing something? I would think the answer would be 799/.0375 and 754/.0387?

Thoughts?
Mike 

 

[allan_wind]

I would use the starting number and validate the calculations by shooting your gun. The BC, I believe, is used to adjust the trajectory, and speed is a variable in that calculation.

 

[Centercut]

Allan_wind, I understand your point, but then I'd have two (or more) entries with the same Velocity and differing BCs. I think if that was the intent there wouldn't be a spot for more than one Velocity, right?

 

[AirSupply]

I’m not sure but is this a possibility. 
Depending on your weather data the velocity of the pellet will vary quite a bit. So you will see that sometimes on your Zero distance Strelok will show you need say .5 click up because the weather is different to the day you zeroed the gun and the velocity is quicker. 
Now when the pellet is shot at different ‘muzzle’ velocities that will have a bearing on the bc. 
So you need to work out the bc when you shot the pellet 
at say 850fps 825fps 800fps at the muzzle. 
Each starting speed will yield a different bc down range. 
Strlok can then us the data to give you the correct bc for the variation is fps the weather causes.
Im just guessing here and if I’m talking bs would also like to know how it works.

 

[Centercut]

I think the intention is to have different BC at various ranges (velocity) and then based on the range you specify in the app it integrates the applicable BCs to give you a more accurate BC for that specific range and uses that to calculate and display holdover. I’m thinking that’s the intent and why just putting in the muzzle velocity for each BC doesn’t make sense. 

 

[AirSupply]

There is an application to true the bc You do it by entering your vertical correction at a distance past your zero distance. It
will then work out your bc based on the pellet drop

Here
If you look at the section for bullet speed you are able to input I think 5 speeds at various temperatures or let it generate a guesstimate for a second speed at a different temperature.
If you put more data in I think it can make a more accurate prediction. 
Bc of the pellet isn’t static and it will vary depending on the velocity you shoot it at. That is on the same day same conditions same gun and same ‘distance’a pellet shot at 830fps will have a different bc to a pellet shot at 850fps.
Thats why you only need the muzzle velocity and bc. 
So at say 50y you use your to crony’s to calculate the bc at 5 different muzzle velocities. Enter this data. (You probably only need 2 at the likely extremes that the pellet may achieve )

Then when you are shooting and it’s hot and your pellets are going 30fps faster Strelok will calculate the bc for that pellet velocity variation. 
This is also why there is no place in the multi bc section to enter a distance. 
The variation you get in your bc at the speed difference due to temperature is going to be small. 

 

[AirSupply]

Thought I’d try this what do you think. 
My Impact is shooting the King Heavies at 880fps with a bc of .057. 
I calculated the bc by shooting over the Chrony to find the speed. Then I zero’d at 50m. 
At 94m I need an elevation correction of 3.14 MRAD
which Strelok says gives me a bc of .057

Now if I drop the speed to 830fps and repeat the above I should get a new bc for that velocity and be able to use that in the multi bc. 
As a percentage Strelok should be able to tweak the bc for the speed differences due to the temperature. 

I’ll give it a go and let you know happens. 

 

[AirSupply]

I did have a look for some info on line. Nothing!

 

[Centercut]

Yeah, it’s confusing. I think you may be on to something. When you look at the Strelok section here. 

So 

You can enter a single BC for your pellet and muzzle velocity or you can select multiBC and it goes here

Now you’re on this screen. Say you’ve calculated BCs at various distances and set up so you measured velocity at 25 and 50 yards. Then you calculated your BC at 25 and 50 yards with those two velocities. So do you enter the velocities at 25 and 50 yards used to calculate those BCs or do you enter the muzzle velocity, which would be the same?

PS. Airsupply, that’s a super high BC. No wonder they’re using the .25 Heavy at EBR. My .30 BC for the 50.1 gr JSB is .053, and I thought that was as high as possible for a diabolo pellet 

 

[Centercut]

I think we are looking at it from two separate view points. You are looking at varying BC for differing muzzle velocities with the same pellet. That does make sense. I am looking at varying BCs at differing velocities at the same muzzle velocity with the same pellet. I’m not sure who is correct.