Weight a factor of BC?

[ndking1126]

Hello, I've done quite a bit of searching so I apologize if this is a duplicate question.

Is weight of the bullet a factor in its BC? For example, if you had two bullets that were the exact same size and shape (ie, all external dimensions were identical) but one was made of a more dense material and therefore weighed more, would the heavier bullet have a higher BC?

If the answer is no, wouldn't the heavier bullet maintain its velocity longer?

 

[Plinker147]

Yes weight it is a factor of BC.

However in your example I doubt there would be enough meaningful difference to matter if external dimensions are the same.

 

[ndking1126]

Yes weight it is a factor of BC.

However in your example I doubt there would be enough meaningful difference to matter if external dimensions are the same.

If you take any given round, let's say .308 in 150 grain, and make it heavier to 165 grain by making it longer, is the extra weight or the extra length what is responsible for the increased BC?

 

[8andbait]

Weight is not a factor. Most ballistic calculators don't even ask weight. BC, velocity and environmental conditions are what matters.

100 gr bullet bc of .600 and a 200 gr bullet bc of .600 will act exactly the same under the same conditions.



Hope that answers your question.

 

[longestrange]

Hello, I've done quite a bit of searching so I apologize if this is a duplicate question.

Is weight of the bullet a factor in its BC? For example, if you had two bullets that were the exact same size and shape (ie, all external dimensions were identical) but one was made of a more dense material and therefore weighed more, would the heavier bullet have a higher BC?

If the answer is no, wouldn't the heavier bullet maintain its velocity longer?

If your bullets are the same size and shape, then they have the same diameter and form factor. If one weighs twice as much, the BC will be double the other one.

SD = w / d^2
BC = SD / i
SD = sectional density
w = weight (not mass)
d = diameter
i = form factor
BC = Ballistic Coefficient

Form factors are much more complicated. G7 BC's are based upon a typical longrange boattail bullet 'form'. G1 BC's based on flat based bullet 'form'. BC's are dependent on velocity as well. You will want to use the G7 BC for a long range boattail bullet if it is published.

Either way, your heavy bullet BC will be double the light bullet BC, since the form factors are identical.

 

[ButterBean]

Weight is not a factor. Most ballistic calculators don't even ask weight. BC, velocity and environmental conditions are what matters.

100 gr bullet bc of .600 and a 200 gr bullet bc of .600 will act exactly the same under the same conditions.



Hope that answers your question.

That's not what he is asking and Weight is a factor, the heavier the bullet the higher the BC, they go hand in hand

 

[ndking1126]

Thanks all, I was discussing this on another platform and was confidently challenged that weight does not affect BC. I was hoping for a response with the technical/mathematical explanation for what I believed to be true and as always you guys came thru. From being a kid, I knew throwing two very similar rocks the heavier one kept its velocity longer, but math is better than opinion. Thanks everyone!

 

[nkyshooter]

Ballistic coefficient - Wikipedia

en.wikipedia.org

I did NOT model it to determine the impact of weight on BC ... feel free to and share it back

 

[ButterBean]

Thanks all, I was discussing this on another platform and was confidently challenged that weight does not affect BC. I was hoping for a response with the technical/mathematical explanation for what I believed to be true and as always you guys came thru. From being a kid, I knew throwing two very similar rocks the heavier one kept its velocity longer, but math is better than opinion. Thanks everyone!

If you take 2 bullet jackets of the same dimensions and fill one with powder and the other with lead, the lead bullet will have the higher BC, it's that easy

 

[8andbait]

I think you guys are confusing BC with energy.

 

[ButterBean]

I think you guys are confusing BC with energy.

Uhhhhhh , Nope

 

[ndking1126]

Ballistic coefficient - Wikipedia

en.wikipedia.org

I did NOT model it to determine the impact of weight on BC ... feel free to and share it back

I read that article! Interesting, but not surprising that it's from someone here. Unfortunately for me, reading isnt the best way for me to learn. You might have answered this question in there and I wasnt able to pull the info out.

 

[ndking1126]

I think you guys are confusing BC with energy

See if you can find 2 footballs of the same size but different weight. Throw them both as hard as you can and see which goes farther. If you dont mess up your mechanics on either throw, the heavier one will fly farther. Same with hitting golf balls. You're not wrong about having more energy. The heavier bullet will also have more energy.

 

[nkyshooter]

You guys made me think (ouch) ...

I think we have a bit of a "both right" scenario going on here ...


Hypothesis to be proven or challenged:
If the BC of 2 different weight projectiles is the same - their flight characteristics are the same regardless of their weight (i.e. same drop at 1000 yards)

Here is the (simplified) equation used to calculate a bullet's BC (based on the wiki page):



BC(projectile) = Mass(projectile) / [Diameter(projectile) ^2 * i(coefficient of form)]


So, that which makes up the BC for those projectiles is in fact a factor of Mass - as well as Diameter and their coefficients of form ...

So, from what I am understanding (so far) on this - 105g 6mm w/ BC of .6 (making this up) and a 140g 6.5mm w/ BC of .6 (making this up) should both exhibit same drop across their path as long as their muzzle velocity is the same ...


So to see if this is correct, I plugged these two into the Hornady G1 calculator ... both with .6 G1 BC ... both at 3000fps muzzle ... leaving everything else the same and only varying the weight and ...

Drum roll ...

... Both have 7.2 mils drop to 1000 - spot on the same

My conclusion - weight/mass is a factor in what the BC actually is - however - for two different weight bullets with the same BC, their drop will be equal if fired at the same velocity.

Somebody correct me if my logic is wrong?