Ballistic Coefficient variability

[Ray B]

the Berger bullet info notes there are three factors involved in a BC: calculation #1, #7 and ratio of form. The older Sierra and other manuals determines BC using a calculation of sectional density and point shape. The newer Sierra manuals use methods measuring velocity loss over specific distances.

Several years ago there was an article in Handloader Magazine that gave a formula for determining BC using two chronographs (presuming that the shooter can put the bullet through both sensor areas).

My question is to those familiar with long range shooting where significant changes in velocity occur: Is there a "best" method for BC and what does it do to make it best?

 

[Standard Velocity]

If I’m not mistaken the manufacturers often have access to doppler radar that tells them the speed throughout flight allowing them to give very specific BC ranges. I would assume Berger and other companies who are popular in competition have this info. Will they share it? I don’t know.

LabRadar is doppler as well. Not sure if it allows you to measure velocity at various distances.

 

[bruce moulds]

can muzzle velocity and drop overs distances be used?
I believe b.c can vary with velocity, twist, and various other factors for the same bullet.
bruce.

 

[Dr Ray]

can muzzle velocity and drop overs distances be used?
I believe b.c can vary with velocity, twist, and various other factors for the same bullet.
bruce.

Interesting point. So members, we need to do some research,

 

[sgt_zim]

If I’m not mistaken the manufacturers often have access to doppler radar that tells them the speed throughout flight allowing them to give very specific BC ranges. I would assume Berger and other companies who are popular in competition have this info. Will they share it? I don’t know.

LabRadar is doppler as well. Not sure if it allows you to measure velocity at various distances.

A good friend has a LabRadar, and yes, it gives you velocity readouts at successive distances. When he's working up loads and shooting at 100 yds, it gives him velocity at 25, 50, 75, and 100

 

[Standard Velocity]

A friend of mine has one too but I’ve never used it. He says it’s a b*tch to set up as it needs to be aimed at the target via the notch on top; akin to using a notch sight on 1” revolver. His fix is a drinking straw placed in the groove. Like boresighting.

Apparently it burns through the battery really quickly. His solution is one of those high capacity backup batteries with USB ports. Some of the better deals are those backup batteries intended to jump start cars. Costco always has them.

 

[Chago]

To prevent me typing a massive amount. Here is a link. If you scroll down a little you will see the entire section on BC. I am not totally understanding what the OP is asking or why. If you are trying to understand what the BC out of your rifle at your velocity is, then yes there is equipment for that. But why? Most ballistic calculators now use G7 functions of Hornady is now even using 4DOF. Which does take this into account. That being said no calculator is 100% accurate and should never be followed on a live animal until you have charted your own dope. Calculators are just meant to get you close as they can never be perfect. This being one of those reasons. I would never shoot at a animal without confirming my data at that altitude(or close to it) and on similar temps. Everything else is not as noticable.


https://www.hornady.com/team-hornady/ballistic-calculators/ballistic-resources/external-ballistics

 

[sgt_zim]

To prevent me typing a massive amount. Here is a link. If you scroll down a little you will see the entire section on BC. I am not totally understanding what the OP is asking or why. If you are trying to understand what the BC out of your rifle at your velocity is, then yes there is equipment for that. But why? Most ballistic calculators now use G7 functions of Hornady is now even using 4DOF. Which does take this into account. That being said no calculator is 100% accurate and should never be followed on a live animal until you have charted your own dope. Calculators are just meant to get you close as they can never be perfect. This being one of those reasons. I would never shoot at a animal without confirming my data at that altitude(or close to it) and on similar temps. Everything else is not as noticable.


https://www.hornady.com/team-hornady/ballistic-calculators/ballistic-resources/external-ballistics

Which is why I repeat, over and over, most people have no business shooting at live animals beyond 300 yards, A.H. members mostly excepted (or so I would imagine).

 

[Tra3]

I’m interested in the answers here as I have lots of questions myself.

@Ray B can you define your question and for what purpose you need to know the answer?

Because variable BC Calculations are based on bullet deceleration at a given velocity you would need a very long range with multiple chronographs to gather your own data as the bullet goes from 3000 fps down to 1500?? fps or so. Some of the ballistics calculators have variable BC included with specifics bullets. The variation makes a difference at very long range, but I don’t think it makes any meaningful difference for hunting with shots less than say 500 yards.