BC distance’s question

[Florida_Man]

Is there a minimum distance to calculate BC?

Could a decent result be obtained from muzzle and 15 yards?


I usually calculate my BC with a Labradar and have 5 distances out to 35 yards to use numbers.
But my Labradar is spotty at best with 177, even more challenging with a sub 12 rifle that doesn’t make much noise. (I try doppler trigger and microphone).
I was going to try and do it with my cheap Chinese chronograph.

 

[Dogowski]

Is there a minimum distance to calculate BC?

Could a decent result be obtained from muzzle and 15 yards?


I usually calculate my BC with a Labradar and have 5 distances out to 35 yards to use numbers.
But my Labradar is spotty at best with 177, even more challenging with a sub 12 rifle that doesn’t make much noise. (I try doppler trigger and microphone).
I was going to try and do it with my cheap Chinese chronograph.

I've got one of the Chinese chronys as well and it has trouble reading 177 ammo. I've got to invest in a better one but I just keep buying guns, lol.

 

[Bladebum]

I'm not sure if there is a minimum distance technically, but I wouldn't do closer than 50 yards personally.

 

[Florida_Man]

I’m using the BC to enter into a NV scope with LRF. It’s going on a sub 12 rifle I use for pesting from 10 yards to 35 yards.

 

[hameditor]

For the HAM Ballistic Coefficient tests, we go from a minimum of 0 Yards to 30 Yards as the maximum. Why not further? Well, extensive pre-testing revealed that it was not possible to consistently record meaningful velocities beyond about 35 Yards with our Labradar unit, particularly for light .177 pellets and alloys.

There's a full explanation of what we do here Ballistic Coefficients

 

[wolfmangreg]

Here's how HAM does it:

HAM’s Ballistic Coefficients are calculated from velocity measurements taken at the muzzle and at 30 Yards. Our test range is at 244 Feet above Sea Level and all testing is done on days when the temperature is between 75 and 85 Degrees F with Relative Humidity between 60 and 80% with minimal to no wind.

Have done it myself a few times using 1 yard & 50 yard velocities.

 

[Hateful McNasty]

I've got one of the Chinese chronys as well and it has trouble reading 177 ammo. I've got to invest in a better one but I just keep buying guns, lol.

Funny mine don't .. but I do see one or 2 guys say there's has Issue. I pretty much use it for .177 most .

I got this kind. First grabbed and most always used .. wish I had a newer one that did fps too.

 

[Florida_Man]

Funny mine don't .. but I do see one or 2 guys say there's has Issue. I pretty much use it for .177 most .

I got this kind. First grabbed and most always used .. wish I had a newer one that did fps too.
View attachment 5125

Set it out at 25 yards and try and record some numbers, good chance you’ll need a new one haha

 

[Hateful McNasty]

Set it out at 25 yards and try and record some numbers, good chance you’ll need a new one haha

All of need is at the muzzle. If I shoot down range and hits what I aim for and groups well I call it good

 

[Spinach]

I also use a lab radar, the trigger mic. definitely helped.
Most my BC figures are only to 25 meters for .177.
Try a trigger microphone. Works for me.

 

[Bladebum]

Serious question here, why do you need an exact BC inside of 35 yards?

 

[Florida_Man]

Serious question here, why do you need an exact BC inside of 35 yards?

I just want the most accurate data to enter into my digital scope with LRF. I shoot 35 and under on a regular basis, but in the event I take a longer shot I can have that

 

[Hateful McNasty]

Ham here did it at muzzle and 30 y

Ballistic Coefficients

Thinking what should change at any yardage shouldn't the math add up the same for this pellet at this speed ?

The bc in there yest chart is one result not changing due to distance or speed .. right?

 

[Florida_Man]

I'm sure it won't change much, I just want to do it myself. it's a hobby and something for me to do.
I'm at about 20 feet above sea level, if there is a hurricane I am at sea level haha

 

[Miles_M]

If you are using the correct reference drag law and taking into account the atmospheric conditions during your test, then any distance will do the job. If you are not doing any of the above then your BC will likely change depending on range. The size of the BC changes will depend on how far out any of the above are.

Of course, with a LabRadar you can get the data output in the form of a CSV file of velocity, time and distance. With that data, it is possible to get a purpose drag law which will be more accurate than any BC, and may enable you to select the best BC for your application. Again you will need to know the atmospheric conditions during the test including wind speed and direction. It is surprising how much difference a 5mph wind can make to your results.

 

[Hateful McNasty]

Some mo rocket science

Drag Coefficient and Ballistics Coefficient Explained - Hard Air Magazine

There was another site after one paragraph I had to stop and pop a Excedrin..

Calculating B.C. with LabRadar. Tutorial on my method.

About the bc changing same d above the projectile bc don't change it's the condition around it .. unless it proforms a metamorphosis from muzzle to ya get ( ???)

 

[Miles_M]

There was another site after one paragraph I had to stop and pop a Excedrin..

Calculating B.C. with LabRadar. Tutorial on my method.

About the bc changing same d above the projectile bc don't change it's the condition around it .. unless it proforms a metamorphosis from muzzle to ya get ( ???)

I could immediately see a few basic mistakes in his method in the video, based on the experience of having to do that kind of analysis for years in my work. First, he put a line fit through the velocity data. The problem with that is that you get a drag curve shape which is totally dependent on the curve fitted to your velocity data, and seeing as the drag curve shape is why you are doing it if you are using the data for a BC, he is immediately spoiling his results. You need to go through the data analysis first to get your drag coefficients and then curve fit the drag coefficient data. Secondly, he ignored wind speed and direction which, as I said before, can give surprisingly large changes in the calculated drag coefficients.
He also, based on the picture of his setup, had two very large metal objects close by which is a total no no, as I found out once after demolishing a sea wall thinking it was interfering with our results only to find it was the small metal shed off to the side of us.