I think assigning one BC number to any pellet is sub optimal at best. In my last big project, I attempted to assign a BC to the korean 24 grain .20 cal. Recorded velocity at muzzle (duh) 25, 50, 75, 100 yards on the same day, same tin. After doing the math, I ended up with FOUR different BC numbers!
Seems that BC "evolves" or is dynamic depending on the duration of the flight. Further, you can NEVER assume that your BC # will be the same from a different rifle.
In my case, I took an average of the 4 numbers (.032) and it's been spot on. Took an entire day, but I've shot with that data for years!
Another variable to consider besides all the usual ones (temp, pressure, elevation, blah blah) is what's called "pancaking". What?
Pancaking is more prevalent in thin skirted pellets fired out of higher powered pcp's. The sudden air blast actually shortens the overall length of the pellet! There was discussion on this topic on the Yellow Forum years ago when pcp's started to really get serious (back when 40fpe was a BFD). Everyone was wondering why their BC data was so far off in their new rifle (me for example, shooting 16gb JSB out of a new Air Ranger)
I guess the moral is that BC numbers should be taken with a grain of salt. Unless it was derived from the same rifle, same power setting, same conditions, it'll only get you in the neighborhood (not even ballpark)
Just wanted to share some hard learned lessons with the group. Might be old news for some.
Brian