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determining/calculating ballistic coefficient

I am hoping to figure out the BC for a particular projectile. It's the 56gr. .355" Inceptor ARC for 380 auto. It's their fluted round nose copper/polymer pill. From the manufacturer, I'm not sure what the data they provide means exactly. In some load data they show "BC / SD - .037 / .067 ". I assume they are saying the ballistic coefficient is .037 with a standard deviation of .067. I don't know what SD means in this case. I haven't learned yet how to figure out BC when the manufacturer doesn't publish the BC forthwith or Google doesn't help tremendously. I am going to play with this projectile and reload it for both 380 and 9mm but I would like to punch the BC into ballistic calculators for some data prior to chronographing it myself. Can someone take me to school?
 

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What's the best way to search for the BC of a projectile? Is there a database published somewhere with a large percentage of common and uncommon projectiles?
 
What's the best way to search for the BC of a projectile? Is there a database published somewhere with a large percentage of common and uncommon projectiles?
You might search air gun slugs and pellets. A couple of different folks offer BC on slugs of about the size you are looking for.
 
If you know the sd and the form factor you can estimate the bc. Sd is a function of frontal area and mass. The form factor I don't have a handle on yet.


 
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What's the best way to search for the BC of a projectile? Is there a database published somewhere with a large percentage of common and uncommon projectiles?
I go to the GRT database for projectiles. They have data on a lot of different bullets, but, not all. Other than that you have to trust the mfg until you can fire some (especially for obscure ones and even more so for small pistol cartridges).

There was a website that you could enter a bullet shape/weight and it would calculate a BC, but, I can't remember where it was. FWIW, it wasn't very close for the cast bullets I was shooting back then.

If you have a Labradar you can use the track data to calculate the BC using the calculator on the JBM website. If you are accurate enough you can use the bullet drop over distance to calculate it.
 
I am hoping to figure out the BC for a particular projectile. It's the 56gr. .355" Inceptor ARC for 380 auto. It's their fluted round nose copper/polymer pill. From the manufacturer, I'm not sure what the data they provide means exactly. In some load data they show "BC / SD - .037 / .067 ". I assume they are saying the ballistic coefficient is .037 with a standard deviation of .067. I don't know what SD means in this case. I haven't learned yet how to figure out BC when the manufacturer doesn't publish the BC forthwith or Google doesn't help tremendously. I am going to play with this projectile and reload it for both 380 and 9mm but I would like to punch the BC into ballistic calculators for some data prior to chronographing it myself. Can someone take me to school?
Can you just shoot it at different distances and create a drop chart? You don't need to know the BC.
 
I believe the OG Labradar unit provides you with multiple distance velocity measurements on the same shot. which can then be used to calculate the BC. Not sure of the new Labradar units still do this, or maybe one of the other radar units?
 
What's the best way to search for the BC of a projectile? Is there a database published somewhere with a large percentage of common and uncommon projectiles?
If it were me, I'd look at similar handgun bullets in a reloading manual and try to approximate from those ... this would probably only get you in the right time zone if not zip code, but unless you're shooting those .380 slugs at 100+ yards, the error would probably make no practical difference.
 
SD is sectional density. The 0.037 is the ballistic coefficient. You can look at the Hornady 90gr XTP and see the BC is 0.099 for a much heavier built.
 
Chronograph your loads with a Lab or Garmin, or any other good unit. Shoot drops at specific ranges, it doesn't matter really what ranges, 25, 50, 75, 100 etc and back into the BC through trial and error using most any free ballistic program.
 
Back in the days before folks commonly ran a chronograph, I ran lots of airgun and pistol bullets over a chronograph at distances to while gathering velocity and drop data. That meant I was risking my personal Oehler Chrono when shooting over it down range.

It was then easy enough to back into a BC value that was "good enough" for practical purposes, but the reason I am posting here is to remind the OP that bullets like this are intended for nearly point-blank range in a self-defense setting where the penetration and ricochet issues are more important. Otherwise, you would run a different bullet type.

These days, hobby level Doppler radar chronographs will often plot the velocity out as far as the instrument can track the bullet, and then they back into the muzzle value. We can use that data to arrive at the BC, and then shoot drop tests to verify the results.

If you have your drops and speeds at practical distances, that data is far more valuable than a BC or any math model results.

May we ask... curious just what goals do you have for running this type of bullet other than running it in 9mm or 380?
 
Unless the pistol caliber is being used in a carbine or a rifle the range where BC comes important is likely beyond the practical useful range of the firearm. IN the case of the 90gr XTP at 750 fps the difference in drop at 50 yds for a 0.099 vs 0.050 BC is 0.1". At 100yds it's 1.5 inches out of approximately 34". In a 3 to 6 inche barrel that's well outside the capability of most pistol shooters. Unless you are Larry Vickers or maybe Jerry Miculek.
 
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