BCs are VERY deceiving. There is no precise repeatable way to measure it like using a caliper or mic to measure a bullet. It's based on the sectional density and a form factor. The problem is that "form factor" isn't a real number that can be fixed with any precision.
If the nose gets slightly damaged it changes, if the shape changes and it does from bullet to bullet in the same box it changes the BC. And to make things worse BC is right ONLY at one given velocity and distance and changes as that velocity and distance changes. So the numbers given by bullet makers for BC is mostly BS.
Then too it makes darn little difference in the real world unless the BC number changes by a lot. In other words the difference between a BC of .3 and one of .4 is really not much even tho much is made over it. As long as the BC is above .3 you gain darn little going higher and only at extreme distances at which few have any real business shooting.
All of that is true. The BC is an approximate given by the factory. Most bullet companies give a number & that's it, Sierra being a Target bullet company at heart will give BC's at varying velocities. If there is any yaw whatsoever, the actual BC will be lower, as it is not flying 100% true. To have a totally accurate assigned BC,
you must test the drop by actual shooting with your gun & of course you must accurately measure the velocity at the same time. This is why many times the BC figured this way can be a good bit lower than the bullet people say & every once in a while it will show to be higher. But the drop varies with altitude as well, don't expect a rifle which was sighted in on the Gulf Coast to be dead on when you hunt on the Cont. Divide.
Remember also that BC has alot to do with wind drift & a high BC bullet can be more important for that reason than for trajectory, which is easier to plot.
Like GB said, at average Deer hunting distance it is usually not very important. I have seen some folks comment that they won't be shooting over 250 yards & in the next breath they are hung up on BC. No need to under those conditions with a reasonable bullet.
