Bullet BC theory- Have you proven it?

[xr650rRider]

I will never be convinced that BC and velocity tell the whole story for windage. Drops, yes mostly. On top of that, tune can change windage. No numbers can predict that.

Math/Numbers can predict anything. It's just how complex is the model. NASA launched a couple spacecraft 48 years ago and they are still flying in space. Voyager 1 is approaching 1 light day away. Somebody had a pretty good calculator and a pretty complex model. A lot of the ballistic calculators we use were for landing a 2 ton projectile on the deck of a ship 25 miles away.

Where Are Voyager 1 and 2 Now? - NASA Science

Both Voyager 1 and Voyager 2 have reached "interstellar space" and each continue their unique journey deeper into the cosmos.

science.nasa.gov

 

[Tesoro]

Quickload, Gordon's reloading tool

Oh. I didnt consider the definition of ballistics being anything to do with pressures, but rather motion/flight characteristics.

 

[xr650rRider]

Oh. I didnt consider the definition of ballistics being anything to do with pressures, but rather motion/flight characteristics.

Propulsion, flight and impact.

 

[TC260]

Math/Numbers can predict anything. It's just how complex is the model. NASA launched a couple spacecraft 48 years ago and they are still flying in space. Voyager 1 is approaching 1 light day away. Somebody had a pretty good calculator and a pretty complex model. A lot of the ballistic calculators we use were for landing a 2 ton projectile on the deck of a ship 25 miles away.

Along that same line, I don't claim to have in-depth knowledge of this stuff but that's my understanding of the 4DOF calculator. A more complex model that fills in the gaps of BC based models.

 

[xr650rRider]

Along that same line, I don't claim to have in-depth knowledge of this stuff but that's my understanding of the 4DOF calculator. A more complex model that fills in the gaps of BC based models.

6DOF would be the holy grail. They are all point mass solvers for intervals along a projectiles motion. So for some interval, maybe every .01 ft, you solve the equations of motion for a body. Dump them into an array and graph them. 6DOF would have every input acting on a body and you would think it would have to be perfect. Problem is, you don't necessarily have inputs for yaw, pitch and roll. We're solving a simple equation with 3DOF and it gets you close, it doesn't absolutely model anything. So use more computing power...............or fire another shot. Never designed for you to punch in some numbers and make a first round hit on the bullseye. Unless your bullseye is the size of a town. Think of the wind drift side, you input a single vector that you have determined some magnitude and direction. You ever watch smoke? How many variables in wind do you think there are between the muzzle and target. Nothing but a WAG (wild-ass-guess). If you use instruments along the way, then it's SWAG.
To see the guys at the Tackdriver shoot sub 0.25 moa groups @ 330 yards. is bordering on sorcery and magic. Lots of experience.

 

[Alex Wheeler]

Math/Numbers can predict anything. It's just how complex is the model. NASA launched a couple spacecraft 48 years ago and they are still flying in space. Voyager 1 is approaching 1 light day away. Somebody had a pretty good calculator and a pretty complex model. A lot of the ballistic calculators we use were for landing a 2 ton projectile on the deck of a ship 25 miles away.

Where Are Voyager 1 and 2 Now? - NASA Science

Both Voyager 1 and Voyager 2 have reached "interstellar space" and each continue their unique journey deeper into the cosmos.

science.nasa.gov

Maybe, Im no expert on that. But the thing Im talking about seems very hard to predict. Different stability based on tune thats changing through out the day or barrels life. And not all barrels can achieve the same level of stability. Thats why theres hummers. Seems like an impossible thing to predict. Outside of the BR world most will deny this is even true.

 

[WSnyder]

I will never be convinced that BC and velocity tell the whole story for windage. Drops, yes mostly. On top of that, tune can change windage. No numbers can predict that.

I’ve been working with a 40cal smokeless muzzleloader recently with a high ish BC (for a flat base) bullet. The drops are right on but I’m getting a fair amount more drift than what is predicted by the solver. I need to go back to JBM and play with entering a different form factor for these bullets and see if there’s anything there. When I initially tried that I didn’t see anything.

 

[WSnyder]

Math/Numbers can predict anything. It's just how complex is the model. NASA launched a couple spacecraft 48 years ago and they are still flying in space.

I’d agree. The PS article “Why BC is BS” I mentioned goes into that. The guy (Randolph Constantine) had to predict very reliably where the space shuttle liquid fuel tank would land after it was ejected. He had to calculate all of the possible permutations of that tank tumbling its way towards the earth.

 

[davidjoe]

does it have anything to do with "proportional speed" ? Like moving in the water. At some point , weight matters more. Unless the ratio is to small in a bullet.

Weight overcomes shape in drift and drop. The shape of a Lapua 155 grain 30 cal and a 16 inch naval cannon round is virtually identical. The muzzle velocity is also very similar, and density if anything favors the small arm, yet the naval gun’s range is on the order of 10X the .308.

But BC calculations capture this. We intuitively know that every dust particle we can see floating around the room is of course denser than its volume of air, and that if we enlarged that same substance by 100X in every direction, it would not float around nearly endlessly before settling down.

I’m not certain exactly why air resistance is not scalable to a given shape and density, without reading up more, but it’s definitely not. Liquids can usually be viewed as merely denser gas in this context.

—————
Edit: on reflection, as to the naval round and .308 of similar velocity and shape, the naval round’s frontal area is on the order of 2,800 times larger, but it weighs on the order of 120,000 times more than the .308. This no doubt accounts for the range disparity.

 

[xr650rRider]

With enough money, you'd have your own Doppler radar that could actually measure the bullet throughout it's flight. No longer rely on lookup tables from the 40's for drag. But the rest of the world moved on to guided munitions where they can steer the projectile to it's target.

Kind of off-topic but also not really. If you wondered where AI and computing is heading. Colossus 2 with eventual 1 million Nvidia GPU's running in parallel equaling 7 times the processing power of the top 10 supercomputers combined.

 

[Steve Donlon]

Weight overcomes shape in drift and drop. The shape of a Lapua 155 grain 30 cal and a 16 inch naval cannon round is virtually identical. The muzzle velocity is also very similar, and density if anything favors the small arm, yet the naval gun’s range is on the order of 10X the .308.

But BC calculations capture this. We intuitively know that every dust particle we can see floating around the room is of course denser than its volume of air, and that if we enlarged that same substance by 100X in every direction, it would not float around nearly endlessly before settling down.

I’m not certain exactly why air resistance is not scalable to a given shape and density, without reading up more, but it’s definitely not. Liquids can usually be viewed as merely denser gas in this context.

I think I was getting out there in never land thinking about shapes of marine life and their speed and the fact that small fish can be quicker than big fish, but big fish with a lower "BC" can be faster, like a sailfish going over 80mph. It was very far in the abstract. Thanks for your input, always glad to hear your take on things.

 

[dgeesaman]

Maybe, Im no expert on that. But the thing Im talking about seems very hard to predict. Different stability based on tune thats changing through out the day or barrels life. And not all barrels can achieve the same level of stability. Thats why theres hummers. Seems like an impossible thing to predict. Outside of the BR world most will deny this is even true.

I suspect that what Brian Litz attributes to ‘BC variance’ (where lower variance is better), may correlate to hummer barrels that ‘put the bullet to sleep’ and ‘cut the wind better’. I visualize them throwing a football with a tighter and more consistent spiral.

Anyway the fact that Brian does a lot of custom drag models instead of selling access to bullet-specific drag models suggests something important about rifle-to-rifle (barrel-to-barrel) differences.

 

[Steel Mover]

Some makers fudge their BC numbers to improve their sales. You really should check the BCs before you hit the field. I am retired from competition but found that some BCs were wishful thinking, not true numbers. Plus the BC changes as the velocity drops with distance. A good ballistics calculator will allow you to change the BC, the scope clicks, and the velocity for your cronograph.
A real BC schedule will have multiple BC levels. A real ballistics calculator will have multiple layers to give you actual scope click adjustments that can be also be changed based on your scope's actual clickes at distance.
Put this together and you should be able to shoot a 500 yard match with a computer a single zero sight setting, no other sight settings and multiple range targets at altitude and wind velocity with wind direction. I shot three World Champoimship matches with the Silhouette Ballistics Program, to test it, worked like a champ. I did test the bullet BC, before the match and developed a match load good in five different match guns that I built. All in 260 Rem, all with 120 SMKs and all with 100% prepared and water capacity matched brass. Powder H-414, velocity 3,215 fps with a SD of 4. Lothar Walther Match, Computer Lapped 1-8 twist SS, 26" barrels.
Yo can check the BC with multiple chronographs setup at different ranges or with a single cronograph and a good ballistics program on a computer against the bullet impacts and the given BC bullet impacts at various distances. Wen they do not match the BCs as given are wrong.

 

[TonyinKY]

Maybe, Im no expert on that. But the thing Im talking about seems very hard to predict. Different stability based on tune thats changing through out the day or barrels life. And not all barrels can achieve the same level of stability. Thats why theres hummers. Seems like an impossible thing to predict. Outside of the BR world most will deny this is even true.

Along with “hummer” barrels there are “magic” bullets too

 

[charlie b]

There are lots of things that happen when you launch a bullet that are not easily predictable. The ballistics programs we typically use are limited, but, some are adding more features, like the Hornady 4DOF mentioned above. 6DOF is common for military research, but, you get in the realm of how much data can you accurately input, such as the wind along the distance of flight. Yep, you can instrument the entire flight path these days (scintillometers), but, it costs a bit of money to do so Then take all that data and input into a good ballistics model.

I'll add in another. Stability. If a bullet is over stabilized it will fly to the target with a positive angle of attack, changing it's BC compared to a bullet with optimal stability. The Army did a lot of research on this with artillery and twist rates to make sure the shell hits nose first. Yes, they still use a lot of unguided munitions. The result is two identical bullets and muzzle velocities with different enough spin rates will have different POI, because the 'real' BC's will be different.

 

[Jr solocam]

The two people on this planet that I won't argue with are Bryan Litz and Elon Musk.

Good luck if you do.......

 

[Tesoro]

Propulsion, flight and impact.

Ballistics not include propulsion or impact in the text books, but maybe at the range

 

[xr650rRider]

Ballistics not include propulsion or impact in the text books, but maybe at the range

 

[charlie b]

There are internal ballistics, external ballistics and terminal ballistics.

 

[jackieschmidt]

Along with “hummer” barrels there are “magic” bullets too

I the realm of Short Range Benchrest, both are “real”.

You will know when you manage to get either.

But then, we don’t play the BC, ES, or SD game. We shoot the most accurate combination we have and rely on flag and mirage reading capabilities to compensate for the lack of BC and other external ballistic aspects.

Set targets at 300 meters., If you give a competent shooter a 6PPC or a BR variant that will honestly Agg below .200, and a set of flags, and give another competent shooter the highest BC combination made, tuned with a great SD and ES, but no flags, the 6PPC /BR shooter will likely beat him every time.

Add another 300 meters, the game changes.