Bullet BC theory- Have you proven it?

[falconpilot]

According to Litz - If bullets of different weights(184hyb vs 215 hyb) and calibers have the same BC and are fired at the same velocity, they will reach target downrange at same time, same speed, same drift and same trajectory. We're going to assume that both bullets are fully stable.

I know some of you have tested this theory and I'm curious to your results??

 

[jelenko]

FWIW, that is a claim of physics, not Litz per se.

 

[SpencerC87]

You can easily go to an ballistics calculator and see the outputs will be the same. I guess you could argue a difference in aerodynamic jump if a 184 is fired from an 8 twist and a 215 is fired from a 10.

 

[Tommie]

100%
Being a subcaliber shooter I continually giggle to myself when people insist that the wind just blows those small bullets into the next county. Of course they don’t actually have first-hand experience but apparently the thought is “well a heavier bullet must be harder for the wind to move”

It’s all about BC and velocity.

 

[Will Henry]

I believe it is also about cross-sectional density. My theory is unproven, but I don't care! WH

 

[centerlineseal]

My theory is unproven, but I don't care! WH

Careful, ... approaching political commentary!

 

[ELR LVR]

According to Litz - If bullets of different weights(184hyb vs 215 hyb) and calibers have the same BC and are fired at the same velocity, they will reach target downrange at same time, same speed, same drift and same trajectory. We're going to assume that both bullets are fully stable.

I know some of you have tested this theory and I'm curious to your results??

Same speed/ Same resistance to air affecting its profile should slow down the same rate
Weight is more of a factor within Stationary Inertia vs Momentum
accelerating a mass from a dead stop or retained energy Once it hits a solid target
---
With the the same BC, the velocity loss per every 100 yards should remain the same
and that is really what BC does for us, allow us to RETAIN as much velocity as possible as it travels
---
You can calculate it just by looking at the velocities every 100 yds...
BC's of Approx. .600 have an average velocity loss of about 4.5% per every 100 yards
---
Interestingly,
Velocity loss per every 100 yds is very linear, even though drop is exponential
With todays High BC bullets, due to this Higher retained energy per every 100 yds
is why Now ...we can start off a lighter 6mm bullet FAST
and Have more energy than an old school 7MM Rem Mag had at 600 yds

 

[Rank Amateur]

I believe it is also about cross-sectional density. My theory is unproven, but I don't care! WH

Right you are! BC is the ratio of sectional density to form factor. Best determined empirically with actual ballistic measurements, but generally calculated as

where “i” is the form factor that describes the bullet shape and other characteristics. So SD is an intrinsic part of BC.

 

[Infrequent Shooter]

I bet Germany, US, Japan and GB studied the heck out of this in the 1920s and 1930s!

 

[BoydAllen]

There is at least one prominent F class shooter that has said that there seems to be a wind drift advantage to heavy bullets that the BC does not account for. I believe that that is the sort of hands on observation that the OP is looking for.

 

[xr650rRider]

Source:
The Ballistic Coefficient by William T. McDonald & Ted C. Almgren December, 2008

 

[gunsandgunsmithing]

"The mathematical formula for finding a bullet’s sectional density is: SD = the bullet’s weight in grains divided by 7000 (because there are 7000 grains in a pound) divided by the bullet’s diameter (caliber) squared"

IOW, heavy for caliber bullets will have better sectional density.

What I've seen is that weight doesn't matter. But, it'd be fairly easy for any bullet maker to test, by varying core weight and the same jackets and keeping velocities the same. Where that gets more complicated is harmonic related. It's not an apples to apples comparison of two different loads, even if both are tuned to shoot small...unless both are releasing at the top of the bbl swing...ie ladder or sine wave testing.

The thing to remember is that bullets don't get pushed by wind, but get pulled due to drag. Same with most anything...windflags and airplanes included.

 

[Tangent]

Is there an element of inertia to all this? It's harder to change the course of anything that has a larger mass.

 

[charlie b]

The military has tested the external ballistics calculations enough that I do not doubt the accuracy of the numbers.

I've measured bullet drop enough to know that the ballistic calculators, given the proper inputs, are accurate for my shooting ability.

 

[falconpilot]

I've read a tremendous amount on this subject and understand the physics behind it, and the theory itself. I know a bit about aerodynamics as related to aircraft, airflow, thrust vectors, drag, yaw vectors, etc.

I'm simply asking if anyone here has laid down with tow different calibers, different weight bullets but same BC, running the same speed, and fired them are side by side targets at exact same time - and compared difference in bullet velocity, drift, trajectory..in other words does the physics/math hold true? If BC is the same, they are both stable, and speed are the same, then they should be the same....

 

[Will Henry]

I have been misunderstood (this applies to my whole life, but this thread is illustrative). I am speaking not of sectional density but cross-sectional density. A round ball demonstrates the same SD from any angle. A cylindrical bullet shows a different SD from the side compared to head on. A larger diameter cylinder has greater cross sectional density than does a smaller one. Of course, the shape and composition of the nose portion of the bullet plays into the whole equation too. How much difference does it make? How the hell would I know?! I'm virtually uneducated and not that smart. This may be why so many of my theories hold little sway with the shooting community. WH

 

[ELR LVR]

Is there an element of inertia to all this? It's harder to change the course of anything that has a larger mass.

Not as it relates to Drag / deceleration
For fun to double check this - I just ran 2 different bullets through an App with same BC
95 grain
115 grain
Both had the same drop downrange if started at the same velocity
---
This is because all things fall at the same rate regardless of their mass
it doesnt matter what the BC is when it comes to drop
Drop is more relevant to "TOF"
---according to the Lapua APP, even wind doesn not seem to affect weight
Now That I do not know why, because intuitively, as you say, a larger mass should be harder to push
but I ran it with a 95 gr and changed that one number to 220 gr
And it called for the same wind adjustment at 1000 yds

 

[dgeesaman]

According to Litz - If bullets of different weights(184hyb vs 215 hyb) and calibers have the same BC and are fired at the same velocity, they will reach target downrange at same time, same speed, same drift and same trajectory. We're going to assume that both bullets are fully stable.

I know some of you have tested this theory and I'm curious to your results??

That is literally what BC calculates.

If two bullets don’t have the same TOF and drop then they don’t have the same BC or at least, don’t follow the same drag law.

David

 

[BoydAllen]

Years ago I suggested how a realistic wind drift test could be done for short range benchrest rifles. Some fellows did the test exactly as described and there were a couple of surprises. Noting trumps a good test. Ballistic formulas are attempts to reproduce what happens when projectiles are fired, on paper. so that changes in the variables produce the same changes in results both on paper and on targets. The kicker is that actual testing requires time, effort and resources that most are not willing to come up with. The good news is that credible testing is well within the reach of any small group of shooters.

 

[Medic505]

I'm curious

Be truthful..... you did this to kick off the winter pissing match contest didn't you.