By BC, I'm assuming they are meaning Ballistic Coefficient, and that it does not change with velocity is not exactly true. What you need to find out is the what speed the bullet was constructed for. Bullet Construction has its designed velocity range. If the bullet is pushed too slow, it won't expand. Pushed too fast and it come apart and fail to penetrate. Those round nose bullets have a lot of lead exposed on the tips and are typically designed for lower velocity than a spitzer. My guess is the range is in the neighborhood of 1500-2500 fps. That's a guess, though. Hornady would know for sure.

I suspect these bullets were designed for the 338 Win Mag and should operate in that velocity class. Tack on another few hundred fps and the design parameters are well exceeded. Throw in all the variables of hide, bone, muscle or no bone and little muscle, and it just makes it tough for one bullet to do all things.