The REALLY, real- real BC

[AlwaysLastPlace]

Edit- thanks everyone for a lot of answers. Before I posted this I did not know enough to simply ask the question any better.
So here is what (or how) I think I should have asked it:
Why does the drag law I am being told, or recommended, to use in certain apps differ?
Why does the bc on the tin not match what the calculator says it will do AND not match what I see in real life?
I have a ton of stuff to go try out now and I don't feel stuck so thanks.

P.S.
Some people are super smart and they like showing off and that can come across as talking down. But I grew up on the less fun end of a one-way range so it's pretty hard to hurt my feelings. I'm new to improving at this level, not 10 years old.
People can be any combination of wrong, right, nice or a big turd about it. It's all paying for education and now I've got homework or else I just wasted everyone's time with a less than optimal question that ya'll kindly took the time to try to answer.
I can tell you all that there are a LOT fewer and less angry know it alls in this world than in real guns, 3 gun especially. Some folks maybe should be nicer and other people maybe need to let more attitudes slide.


Guys and gals I have been doing my homework which means I have tried figuring it out on my own before bothering you fine folks.
I have a chrony built into my barrel and one at 25 yards.
I am using JSB Exact 44.75gr, a well calibrated mg scale and a brand of micrometer for head size that is so German I'd get kicked out of Disneyland (again) for saying it out loud. What am I doing wrong?
I'm getting bcs from low .03s to mid- high .04s.
I've read some things that are way too complex that I don't have equipment for, radar and such, but we have been figuring bc on paper forever.
What do I do? I intended to go through all my JSB weights and play on all the ballistics calcs to scratch my autism itch for the day but I never got past the JSB exact 44.75.
Frustrated in Fenix

 

[AlwaysLastPlace]

All of the drag laws mentioned above can be found in free, openly available software for phones and laptops. It costs you nothing. The problems arise when fire arm apps, which do not have the correct drag laws, are used for pellets.

New drag laws for pellets have not been coming out for decades. GA was the first one to replace the previous constant Cd methods which had been used up till then. Follow on ones such as GA2 and WC0 have been created in the last few years in an effort to help average guys to use the free apps readily available. The same with the slug specific ones SLG0 and SLG1. RA4 is for rimfire, but seems to work OK for slugs at most velocities. None of the drag laws will be perfect, but for 99% of applications they will be an improvement on what was available before. You do not need purpose drag laws for every pellet design, and there is very little software available which can use purpose drag laws if you had them.

Obviously for some people we have just been wasting our time.

I have found them for free as you said but I am at the beginning of learning to use them.
What apps do I have? All the free ones.
If I were to pay for one PC or Android what would it be? But I'd prefer one that I could grow into rather than one that I already have to know everything to use it including solving navier-stokes before I can really use it.

 

[AlwaysLastPlace]

Yes, and what's worse is that they print the BC on the box or in the description of the projectile they're selling and they typically never specify what drag model was used.

stovepipe

Is it just me or is jsb being too conservative? I don't have 30 + inches of drop at a 100 yards. But if I use the .03 whatever number JSB says that is what shows up on the calc. Oh wait maybe I should just use their number and change only the drag law (a term I just learned) to back into what drag law they used? That could keep me busy for a while! I'm not really looking for the answer just a direction to head in learning that seems not to be a waste of time. Which is totally subjective.

 

[AlwaysLastPlace]

In this youtube video, Keith Gibson gives an overview of how he uses the Strelok Pro ballistics program. The important thing to get from this video is that he has to use MULTIPLE ballistic coefficients in order to get the program to closely match his real-world D.O.P.E. (data on previous engagement).

The commonly-used external ballistics models (GA, G1, G7, etc.) are clunky general-purpose models that will RARELY be an exact match for a given projectile. Even if one of these models is a close match for a given projectile, the model will only be valid for a limited velocity range. Outside of this velocity range, the model will "fall apart".

Your D.O.P.E. comes first -- you took the shot, you took notes, it's real (or at least it was at the time). Trying to get a ballistics program to agree with your notes can be time-consuming, but it CAN be done.

stovepipe

Are you aware of any way to get Strelok anymore?

 

[JungleShooter]

Are you aware of any way to get Strelok anymore?

Through the Samsung Galaxy app store.

Or installing it from an .apk file (➔ PM).

Matthias

 

[dgeesaman]

This is interesting. I have figured out how to take raw shot data from LabRadar and all of the downrange velocity data and clean it up. (If you have a LR, it uses very simple math to give you downrange velocity. The radar data past 50y gets a bit choppy and their math increase the effect of that error).

So with smoothed and sensible downrange velocity data I’m looking forward to comparing it high quality ballistic models. Maybe, for once, the ballistic model, the LabRadar data, and actual holdovers will agree!

 

[Ballisticboy]

This is interesting. I have figured out how to take raw shot data from LabRadar and all of the downrange velocity data and clean it up. (If you have a LR, it uses very simple math to give you downrange velocity. The radar data past 50y gets a bit choppy and their math increase the effect of that error).

So with smoothed and sensible downrange velocity data I’m looking forward to comparing it high quality ballistic models. Maybe, for once, the ballistic model, the LabRadar data, and actual holdovers will agree!

Be careful how you smooth the data. The answer you get will often be distorted by the smoothing method used, to the extent that any drag curves you get can be completely the wrong shape. The only reason I know this is because I had to spend years analysing thousands of radar tracks and, at first, sometimes getting the wrong answers, not really what you want when you are producing fire control data. Many were obviously wrong, some demanding new laws of aerodynamics to explain them if they were correct (I even had one which required accelerating bullets).

The best method I found in the end was to take the unsmoothed data, carry out the analysis, and then smooth the final results. At the furthest ranges, you will probably end up having to do it by eye, as it gets more than the smoothing routines can deal with.

 

[Scotchmo]

Is it just me or is jsb being too conservative? I don't have 30 + inches of drop at a 100 yards. But if I use the .03 whatever number JSB says that is what shows up on the calc. Oh wait maybe I should just use their number and change only the drag law (a term I just learned) to back into what drag law they used? That could keep me busy for a while! I'm not really looking for the answer just a direction to head in learning that seems not to be a waste of time. Which is totally subjective.

You might be mixing up POI with drop. At 100yds, 30inches of drop is about right for a subsonic pellet with a 0.03 BC.

Once sighted in at say 25 or 30yds, you have already set a significant amount of drop compensation. So you’ll only need another 12moa (approximately) of additional correction. That 12moa is not your total drop.

You probably have a time of flight of around 0.4 seconds. 30” is about how far something falls in that brief period of time.

 

[Stubbers]

You might be mixing up POI with drop. At 100yds, 30inches of drop is about right for a subsonic pellet with a 0.03 BC.

Once sighted in at say 25 or 30yds, you have already set a significant amount of drop compensation. So you’ll only need another 12moa (approximately) of additional correction. That 12moa is not your total drop.

You probably have a time of flight of around 0.4 seconds. 30” is about how far something falls in that brief period of time.

Gravity, makes our projectiles and balls droop given enough time.


-Matt

 

[Stubbers]

Multiple-BC use is very valid over long distance shooting, it's not an opinion, rather fact, no drag model I know of perfects this, however most ranges airguns are used, its negligible, but as people push further and further, Mutli-BC should not be left in the dust or forgotten.


Also worth noting, behind the scenes for ballistic / trajectory programs calculate an adjusted bc which takes into account your environmental conditions such as altitude and temperature, but they do not calculate new bc's for drops in velocity during the time of flight, which is up to the user to input with multiple bc's. It's why some manufacturers (not pellet) will list multiple bc's for different speeds, so you can use these in your calculations.

So, often times, if your having to fudge your bc, its more often than not your environmental factors are not inputted correctly (possibly due to deviance from where the manufacturer tested their listed bc), or your shooting at a very different speed than the manufacturer did for their testing. Once you determine your bc, a good ballistic program shouldn't need any more changes to that based on where you zero, provided they compensate for the enviromental changes and you input them correctly.

-Matt

 

[Scotchmo]

Multiple-BC use is very valid over long distance shooting, it's not an opinion, rather fact, no drag model I know of perfects this, however most ranges airguns are used, its negligible, but as people push further and further, Mutli-BC should not be left in the dust or forgotten.


Also worth noting, behind the scenes for ballistic / trajectory programs calculate an adjusted bc which takes into account your environmental conditions such as altitude and temperature, but they do not calculate new bc's for drops in velocity during the time of flight, which is up to the user to input with multiple bc's. It's why some manufacturers (not pellet) will list multiple bc's for different speeds, so you can use these in your calculations.

So, often times, if your having to fudge your bc, its more often than not your environmental factors are not inputted correctly (possibly due to deviance from where the manufacturer tested their listed bc), or your shooting at a very different speed than the manufacturer did for their testing. Once you determine your bc, a good ballistic program shouldn't need any more changes to that based on where you zero, provided they compensate for the enviromental changes and you input them correctly.

-Matt

When I was using G1 for my .257 slugs, I used the Strelok multi-bc function and it worked well. Later, I switched to RA4 in Strelok and a single BC value worked close enough so I did not even bother with multi-bc.

If your drag model is a poor match for your projectile, multi-bc is a workable bandaid. If you use multi-bc, the drag model does not have to match well at all. So use whichever drag model you want. But you will usually have to get the BC values yourself for multiple velocities, and that’s more work.

 

[Stubbers]

When I was using G1 for my .257 slugs, I used the Strelok multi-bc function and it worked well. Later, I switched to RA4 in Strelok and a single BC value worked close enough so I did not even bother with multi-bc.

If your drag model is a poor match for your projectile, multi-bc is a workable bandaid. If you use multi-bc, the drag model does not have to match well at all. So use whichever drag model you want. But you will usually have to get the BC values yourself for multiple velocities, and that’s more work.

Multi-BC are objectively useful based on subjective experience, but there is no ballistic coefficient model that completely rules out the need entirely for everyone, objectively, however a good ballistic model could try to do it for you.

Add to that, the lower the bc of a particular projectile, the more it would benefit from multi-bc inputs in your ballistic program, due to the increase in velocity change between muzzle and target.

I think often times, people adjust their bc to get real world acceptable dopes at longer ranges, basically averaging what would be the use of 2 bc's, ie: .045 + .047 = .046, and then calling it good, without knowing, which then throws off their close range inputs. This is the band-aid you speak of. YMMV.

-Matt