Nosler's ballistic coefficients

[McInnis]

How does Nosler determine the ballistic coefficient of its bullets? Do all bullet makers use the same method? I ask because when I compare a 180 grn Partition Protected Point to a 180 grn Speer Grandslam, the bullets appear to be very similar (from the outside). They both have flat bases, blunt tips, and almost identical overall lengths. Yet Nosler states a BC of 0.361 for their bullet while Speer states 0.416 for theirs.

Not that I think it's a big deal for the kind of hunting I do , but I do find it curious. :?:

 

[LoneStar]

I do not know which method Nosler uses, but the industry normally either compares the shape of the bullet to various standard models and uses that information to mathematically develop the BC, or they actually fire the bullets and measure the bullets' average decelleration. From that data they can develop the actual BC. Because the bullet differs from the "standard" projectile used to define all BCs, it's own BC will change with velocity. Thus a single BC for a bullet is not really accurate since it chages with speed.

Besides overall shape the weight of the bullet matters, as do very minor differences in ogive length and shape. The visual method of determining BC leaves a lot to be desired.