Venture me a G7 or AB "like" Ballistic Coefficient for these bullets please?

[ceruleanblue]

Friends, I e-mailed both factories (Fiocci and CBC) and the best I could get was a G1 coefficient for one of the bullets. Can you guys venture a G7 BC for each of the two bullets below? Even better would be a similar in the Applied Ballistics universe that I could select to use in building my profile. They are modern day bullets from military cartridges sold by the container to governments around the world, so there must be something quite similar in the existing commercial BC's. I drew the tips as triangles, so please look at the photos to get an idea of the shape of the ogive. Weights and other data I added to my lame drawings. Measurements I took with a digital caliper.
I will then use these G7's and calibrate the results with the "Calibrate Muzzle Velocity" on the Kestrel to fine tune a cocktail that works.

As always, I am most grateful for your help!

Migs

 

[_Windrider_]

Why not just use the G1? You can’t get a G7 by just making something up

 

[ceruleanblue]

Why not just use the G1? You can’t get a G7 by just making something up

I was thinking that this might be a thing of matching a known geometry or finding something similar. God knows I have no idea of how a G7 or AB BC is calculated. I ask because that's what I have and you guys (and gals) are the ones in the know.

 

[_Windrider_]

I was thinking that this might be a thing of matching a known geometry or finding something similar. God knows I have no idea of how a G7 or AB BC is calculated. I ask because that's what I have and you guys (and gals) are the ones in the know.

They use Doppler radar. G1 is basically a formula. Nothing wrong with it. Just maybe not as accurate out of the box. G1 and shoot

 

[Lowlight]

G1 has real value,

I continue to use G1, the only time I don't is using certain AB profiles, but really I always use G1

If it auto adds a G7, fine, but I have to go looking, I look for G1,

G7 is useless beyond software, G1 is not

 

[6.5SH]

If you have a LabRadar you can calculate a G1 or G7 that is valid for as far as you can track it (maybe 120ish yards on .30 cal).
Is useful for when no data exists or is easily findable (common with surplus ammo) or the stated average BC was way off for shorter ranges (unlikely).

JBM - Calculations - Ballistic Coefficient (Velocity)

www.jbmballistics.com

As stated above if you have valid G1 info already there is no reason to get wrapped around the axle.

 

[Lowlight]

You cannot use a Labradar to determine BC...

It's too short a distance you'll always have the best bullet on the planet

You need beyond 300 yards for the second number and further is better

You can do the math backwards, but it's time consuming

 

[DairyDictator]

Lowlight nailed it

BC's decrease as a bullet slows, so determining a BC at a distance a LabRadar can pick up won't do you much good.

I like to run G7 in software if it's available, but I usually just end up throwing the number in software and forgetting it. I use the G1 for purposes of wind, so if you asked me I could tell you my G1 but probably not my G7.

 

[6.5SH]

Guys need to read what I said closer.
Yes there are caveats. No it won't (and can't replace) a well measured average BC from the vendor such as Hornady.
It will however give you a valid starting number out to the distance which you can track (100 yards is pretty easy on a non cluttered range if you aim the unit even with .224).

Need to get the backup srl off a friend's phone so can attach a real world example done with some surplus ammo we couldn't find data on. It gave a better place to start then true from than just choosing random similar weight surplus ammo.

Another example I do have at hand was for Frontier 62 gr BTHP Match.
Near velocity (0 yds) was 2905 fps, Far Velocity 2657 (80 yds), G1 calculated as 0.284 Hornady lists that component as 0.270
Given we all know BC is also determined by velocity and we only have a short velocity range which would drive the BC higher that is still a pretty damn close number. Well within the "adjust the middle number one or two" truing method. FWIW this range was cluttered so 80 yds was as far as I could track a small diameter.

 

[ceruleanblue]

Friends: I don't have a Lab Radar (yet). I need a starting point. Some value to start a profile that I can later correct. Let me ask the question a different way: What would you all do with the information I have? Let's assume we don't have any BC at all.

 

[KnowNothing256]

Friends: I don't have a Lab Radar (yet). I need a starting point. Some value to start a profile that I can later correct. Let me ask the question a different way: What would you all do with the information I have? Let's assume we don't have any BC at all.

Zero it and walk it out to long range, then modify the BC in your software til your DOPE matches. Probably need two different BC regimes, say out to 600 then 600-1k.

 

[_Windrider_]

Friends: I don't have a Lab Radar (yet). I need a starting point. Some value to start a profile that I can later correct. Let me ask the question a different way: What would you all do with the information I have? Let's assume we don't have any BC at all.

Just use the G1 BC you already have. since you dont have a chrono, all you can do is tweak the MV in the calculator to match your real world DOPE. Like the last guy said. Shoot from 0-1000 and tweak the MV to match your actual drops.

 

[ceruleanblue]

Zero it and walk it out to long range, then modify the BC in your software til your DOPE matches. Probably need two different BC regimes, say out to 600 then 600-1k.

ELI5 (Explain like I'm 5) - I need a BC to start with in my AB app.

 

[ceruleanblue]

Just use the G1 BC you already have. since you dont have a chrono, all you can do is tweak the MV in the calculator to match your real world DOPE. Like the last guy said. Shoot from 0-1000 and tweak the MV to match your actual drops.

For the other bullet I have no BC at all.

 

[_Windrider_]

For the other bullet I have no BC at all.

I mean they are probably pretty close. Just use the same BC for the one you have and do the same thing. The reality is it doesn’t matter what the numbers are that go in the ballistic calculator, what matters that the calculator matches your actual DOPE. Remember you are trying to make the calculator match the real world data, not make the real world data match the calculator.

 

[KnowNothing256]

Sorry, didn't realize you don't have a MV/chrono.

 

[ceruleanblue]

I mean they are probably pretty close. Just use the same BC for the one you have and do the same thing. The reality is it doesn’t matter what the numbers are that go in the ballistic calculator, what matters that the calculator matches your actual DOPE. Remember you are trying to make the calculator match the real world data, not make the real world data match the calculator.

Ok, thank you.

 

[Lowlight]

You can do all this from drop

We do it in most classes, you don't need any data, you can invent data to start and then just TRUE the computer based on your drops.

Or you can use Weaponized Math and forget all of it with no inputs beyond 300.

But for a 6.5CM

just use 2750fps and a BC of .300 G7 then true the MV at 600 yards with drop and the BC at 800 with drop

This is a math formula you can solve for the missing pieces because we have the rest of the equation

 

[ceruleanblue]

You can do all this from drop

We do it in most classes, you don't need any data, you can invent data to start and then just TRUE the computer based on your drops.

Or you can use Weaponized Math and forget all of it with no inputs beyond 300.

But for a 6.5CM

just use 2750fps and a BC of .300 G7 then true the MV at 600 yards with drop and the BC at 800 with drop

This is a math formula you can solve for the missing pieces because we have the rest of the equation

Thank you. It is beginning to make sense now. -Migs