About Ballistic Coefficient

[Koda]

For me, using bullet makers estimated published BC along with my own chrono data, Kestrel readings and ballistic calculator has given me as good of results as I'm capable of taking advantage of even beyond 500 yards. No amount of data or equipment is going to make me shoot better, just more practice, which I don't do enough of anymore.

This will work for me then. I just need to get behind the trigger and see what my actual drops are and compare to the advertised BC before I order any custom turret.

 

[BigGame]

The three legs of the stool are muzzle velocity, BC, and drops at distance. If you have two, you can predict the third. Typically we use muzzle velocity and BC to predict drops at distance. But you can just as easily use muzzle velocity and drops at distance to predict BC in the manner already described here (and already noted that you must test the precision of your scope adjustments to truly record observed drops).

Recording velocity at the muzzle and down range is another method for predicting BC. Just plug the two velocities and atmospheric info into this calculator: https://www.jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi

You can use a LabRadar to get both near and far velocities with about 80-100 yards of separation. The LabRadar folks say they don't recommend this method, but I've done it several times and it has provided useful BC estimates that have been confirmed by drops.

And I do believe that the same bullet can have different BCs coming out of different rifles. While BC is generally a function of the bullet's shape and resulting drag, keep in mind that real bullets are deformed somewhat when traveling down the bore through the rifling. One rifle with a slightly tighter bore than another rifle might well see slightly different BCs with the same bullet, though the difference will be small enough to only matter at longer distances (say, 600+ yards).

 

[Koda]

The three legs of the stool are muzzle velocity, BC, and drops at distance. If you have two, you can predict the third. Typically we use muzzle velocity and BC to predict drops at distance. But you can just as easily use muzzle velocity and drops at distance to predict BC in the manner already described here (and already noted that you must test the precision of your scope adjustments to truly record observed drops).

Recording velocity at the muzzle and down range is another method for predicting BC. Just plug the two velocities and atmospheric info into this calculator: https://www.jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi

You can use a LabRadar to get both near and far velocities with about 80-100 yards of separation. The LabRadar folks say they don't recommend this method, but I've done it several times and it has provided useful BC estimates that have been confirmed by drops.

And I do believe that the same bullet can have different BCs coming out of different rifles. While BC is generally a function of the bullet's shape and resulting drag, keep in mind that real bullets are deformed somewhat when traveling down the bore through the rifling. One rifle with a slightly tighter bore than another rifle might well see slightly different BCs with the same bullet, though the difference will be small enough to only matter at longer distances (say, 600+ yards).

super helpful. I should have looked closer in JBMs website for that calculator. I have two chronos so I could someday set one up at 100yds with the target and get 2 velocities.

as far as using my drops I tried playing around with adjusting the BC in the ballistic calc I use but its not matching. With my 100yd zero I dial 3 clicks to hit a 200yd target is 1.6" drop. Adjusting the BC to match that isnt working. Im just hoping to get a close estimate on hitting the gong at 3,4,500yds without wasting ammo dialing.

 

[BigGame]

as far as using my drops I tried playing around with adjusting the BC in the ballistic calc I use but its not matching.

When using drops to predict BC, you need to stretch out out distance. Trying to discern differences between 100 and 200 or 300 is tough because the drops are small so any error in your measurement clouds things. Try shooting at 500+ yards with a reliable scope. Take your time with a good rest, shoot a group (maybe 10 shots?), and find the center point of your group. Drops will be big enough at longer distances to gauge BC your getting.

 

[BigGame]

And be absolutely positive that your 100-yard zero is exactly on at 100 yards before you start.

 

[Koda]

When using drops to predict BC, you need to stretch out out distance. Trying to discern differences between 100 and 200 or 300 is tough because the drops are small so any error in your measurement clouds things.

ah, makes sense... its a resolution thing. 1/4moa click at 100yds is barely noticeable but at 500yds its over an inch...

I was getting sub moa but I tweaked my handload but Im still zeroed exactly at 100 and was hitting about 1moa out to 200yds last time without a led sled. I should be 12 clicks at 300 (old handload)... so im playing around with the calc and think I can estimate clicks at 4 and 500yds.

 

[P7M13]

Rabbit hole stuff:

Extensive Field-Tested Rifle & Cartridge Research - BallisticStudies.com

Expert rifle & cartridge research, carefully compiled through extensive field-testing & freely offered to the firearms community.

www.ballisticstudies.com

Education - Applied Ballistics

appliedballisticsllc.com

Search | arXiv e-print repository

arxiv.org

 

[ferret427]

Rabbit hole stuff:

Extensive Field-Tested Rifle & Cartridge Research - BallisticStudies.com

Expert rifle & cartridge research, carefully compiled through extensive field-testing & freely offered to the firearms community.

www.ballisticstudies.com

Education - Applied Ballistics

appliedballisticsllc.com

Search | arXiv e-print repository

arxiv.org

+1 for anything Applied Ballistics. Wish they still were putting out the free white papers.

 

[DizzyJ]

To add to this I want to order a custom turret dial and while I might not need to shoot past 500yds right now I want it to be accurate at any distance.

This will get you close but only for one elevation and one temperature.

When those change your turrets will no longer be accurate at longer distances.

 

[Koda]

This will get you close but only for one elevation and one temperature.

When those change your turrets will no longer be accurate at longer distances.

True, but I get a free turret with my scope purchase. Other than that I will just use the normal turret with my ballistic app.

 

[DizzyJ]

This guy would be a good source if you're wanting to delve into this field.

Meet Our Ballistician, Bryan Litz

One of the key components of our winning team, Ballistician Bryan Litz, is known by many to be the top ballistician in the country, and arguably the world.

bergerbullets.com