Originally Posted by 458 Lott
Originally Posted by cra1948
I wouldn't go so far as to say SD is meaningless, but in and off itself it doesn't tell anything.


You say sd is not meaningless, but then go on to say it doesn't tell us anything? That is the dictionary definition of meaningless.

Originally Posted by cra1948

It's like such things as standard deviation and ballistic coefficient.....yeah, we know what those things mean, but they are only relevant as minor and individual components of a much bigger picture. In isolation they are useless to the boots on the ground guy (most of us here) in determining what works best for us. (But they do sound profound tossed into the gacklian discussions.) For our purposes the only thing that works is experience. You identify a range of calibers/bullets/loads that work and within that range bullet placement is the final trump card.


Balistic coefficient most definitely is a meaningful number. Bullets of different bc will drop at different rates, and arrive at different velocities. Hence it is a meaningful number that correlates to the performance of a bullet.

Just because someone can calculate a number doesn't mean that number is valid to the what we want to know or communicate. Why sd is meaningless is that the shape of the bullet, the construction of the bullet and the impact velocity of the bullet all strongly affect how a bullet performs, and none of those factors are used to calculate sd.

On the surface sd seems like it should be a meaningful number, and people that have lots of hunting experience have touted using it as a meter to predict terminal performance. On the surface it sounds great and has been promoted by people that have lots of experience. The trouble is applying a more thorough analysis shows that the number falls far short of providing a useful means of predicting bullet performance.


I qualified my statement by saying "in and of itself" it doesn't tell us anything. Examining bullet performance from a strictly academic perspective, sectional density probably provides a useful coefficient for use in some calculations. For our purposes, not so much.
In the case of ballistic coefficient it's the same deal. In and of itself, in the absence of other data, it's useless. We couldn't very well say, "This bullet is better than that one because it has a hight BC." There's a whole lot of other factors involved in making that decision: what caliber, what velocity, how does the BC hold up when velocity drops off, what's the bullet construction like?
My point was, none of these factors, in isolation of other factors, is worth much to us. Sorry if I didn't make that clear.

Mathew 22: 37-39