What is "BC" and "SD" ?

[Dubious_Beans]

In the Lymans 49th edition, all of the recipes have the initials BC, and SD in the upper right corner followed by a number .

For example:

115 gr JHP

BC: .129

1.090" OAL

SD: .130

I get the OAL part, but I don't understand what "BC" and "SD" mean and how it relates to my loads.
I can't seem to find the definitions anywhere in the text of the book.

Can someone please toss me a clue...

Thanks!

[Boots]

BC stands for Bullet Coefficient - how much it drops or rises in flight.
SD stands for Sectional Density

[Rogu3]

BC stands for Bullet Coefficient _ how much it drops or rises in flight.
I forgot what the SD stands for

Ballistic coefficient is how the given bullet flies compared to the standard bullet (BC 1.0) , SD is sectional density.

[bombadillo]

Beats me, all I can think of for my line of work would be "Sagittal depth" for the fitting of contact lenses.

[pisarski]

standard deviation

[Boots]

To better explain SD, as from the Sierra 5th edition manual:

A bullets weight, in pounds, divided by its diameter in inches squared. High sectional density is essential to producing a good ballistic coefficient and deep penetration.

[Rogu3]

I have 3rd edition =p

[Fjold]

Ballistic Coefficient (BC) is a measure of the bullet's ability to overcome air resistance in flight when compared to an "ideal" ballistic model. The higher the number, the less air resistance it has.

Sectional Density (SD) is a comparison of a bullets mass to it's cross sectional area. It's usually used as an indication of how well a projectile will penetrate.



Bullets don't rise in flight, gravity works.

[Boots]

Bullets don't rise in flight, gravity works.

True, I guess I should have elaborated and made the reference to how high above or below a point of reference. For example, if you're at 0.0" at 200 yds you may be high at 100 yrs but lower and lower beyond 200 yds.

[killshot44]

True, I guess I should have elaborated and made the reference to how high above or below a point of reference. For example, if you're at 0.0" at 200 yds you may be high at 100 yrs but lower and lower beyond 200 yds.

Zero-point has nothing to do with Ballistic Coefficient or Sectional Density...

[SixPointEight]

Zero-point has nothing to do with Ballistic Coefficient or Sectional Density...

True, but bullet drop does. I think that's what he's trying to indicate.

Higher BC will maintain it's velocity better, buck the wind better, and drop less than a bullet with a lower BC.

[CoyoteHunter555]

True, but bullet drop does. I think that's what he's trying to indicate.

Higher BC will maintain it's velocity better, buck the wind better, and drop less than a bullet with a lower BC.

BC, SD, Sight Height, Environmental Conditions, Altitude, Angle, blah blah blah are all puzzle pieces leading to the big picture, your POI

[Dubious_Beans]

Thanks everyone for setting me straight about "BC" & "SD".

Much appreciated!

[Boots]

True, but bullet drop does. I think that's what he's trying to indicate.

yes, thanks... that's what I (badly) was referring to.