Getting back to this because it's important.
You cann't just add weight in the middle of the bullet.
But you can. The added length in the middle does very little aerodynamically. It can add a little skin drag, but it's a small percentage of the overall drag and not very significant relative to the increase in SD. There are computer programs that model and predict this, even online calculators but more importantly we can see it in actual bullets. Take a line of bullets, like the 30 Cal AccuBonds for example from back when their ratings weren't so screwy, or SMK's of any caliber being careful to pick out the similarly shaped ones since their testing has historically been pretty good. Plot the points, draw a best fit line and you'll see the general trend is clear. Of course each bullet won't land
exactly on the line, but the trend is followed. Ones that are far from the line can often be shown to have subtle differences in shape or simply a rating that's a bit off.
Now this is a good thing. This is what allows us to have high BC bullets. Otherwise anything but the lightest bullets would need to be rediculously long and would have trouble competing with the lighter bullets with the small improvement in form factor not making up for the slower muzzle velocities.
Of course lengthening the nose and tail increases BC
even more, but in addition to cost, you run into some practical difficulties pretty quickly with twist, OAL, etc. Remember the 338 RUM's case was shortened specifically because the 300's was too long to fit in the OAL target with the long ogive 338 bullets. Naturally, that means it's a no-no for Nosler in this case.
And also, you mentioned the aluminum tipped bullets. Their noses are longer and pointer than normal bullets which naturally helps their BC compared to those. But when compared to each other, as far as I know the Hensons, for example, do have the same noses and tails in each caliber—just weight added in the middle. So there's another example why it's good thing that's all it takes to significanly increase their BC's, otherwise the heavier ones would never make up for their lower velocities.
