Ballistic Coefficient

[Intruder]

For those of you who are really into reloading....
I've been hearing through the grapevine that the BCs published by the bullet manufacturers are often overstated. 

From what I've been able to gather there is no real standard on how companies have to measure BC.  What they are supposedly doing is when they're calculating the BC there's a constant that needs to be applied to the BC calculation called Drag Factor (or sumthing like that).  Anyway, they are using Drag Factors that are favorable but not necessarily representative. 

One of my friends has gone so far as to go out and do some shooting w/ 2 chronographs to determine BC himself on some bullets.  He was prompted to do this because a couple years ago Barnes went through and reccalculated the BCs on all their bullets.  Their published BCs dropped dramatically.  My buddy was so pissed he started doing his own measurement and found that the new Barnes figures were right on the money (even slightly understated sometimes) and that many of the other bullets that had significantly higher published BCs where often grossly over stated. 

It would be nice to see the industry comply to an independent testing body for BC calcs.  Until that happens it may be wise to keep this in mind when lookin at the published BCs out there.

[high country]

sierra is pretty good about it. the fact is that bc is not a constant. it changes with velocity. your buddy is doing the right thing wit the 2 chrony's. I would just suggest getting to the range and shooting at all the various distances and using that to plot your map. keep in mind that baro pressure, altitude, temp, humidity, azimuth, are all factors too secondary to distance, velocity and wind. it gets complicated after about 600 yards.

[littletoes]

The problem stems from the use of the old G1 models, but people are so use to them, they don't want to upgrade to the newer G8, G9, etc. etc. stuff that the new programs can use.

Older G1 stuff is based off of round nose projectiles such as was used during WWII, not the newer tangent/secant ogive stuff that is more streamlined.

Hence the reason Sierra Ballistics uses more than one BC for differant velocities for a given projectile.

I also would second that Sierra does a very good job.