vette78

[vette78]

I have a question that is bugging me, I recently purchased lymans 49th edition reloading manual and in pistol section they show a drawing of the cast bullet above the load specification next to the bullet there are specs for example next to the 200 grain swc it says BC.063 and under that SD.140. does anyone know what there numbers refer to?? Probably something really simple but I can't figure it out.

[Vly]

The BC is the ballistic coefficient. In simplest terms it is a representation of the projectile's ability to overcome the resistance of the air. The SD is the sectional density.

Most good reloading manuals tell how to use these numbers in calculating trajectory.

[vette78]

thanks Vly I really appreciate that. It was realy bugging me.

[MtGun44]

BC is ballistic coefficient which tells you how high the aerodynamic drag
will be, so you can calculate the velocity loss.

The SD is sectional density which has to do with the mass of the bullet
compared to the frontal area. A low SD projectile like a sphere will
penetrate in meat less than a high SD projectile like a 175 gr 7mm boolit,
or for an extreme example, and arrow. You can shoot all the way thru
an elk with an arrow at about 300 fps, but a 30 cal lead sphere (1 buck)
will penetrate maybe 8-10" at about 1200-1300 fps.

Bill

[jhrosier]

There is quite a bit of information about ballistic coefficient here: http://en.wikipedia.org/wiki/Ballistic_coefficient

And about sectional density here:
http://en.wikipedia.org/wiki/Sectional_density
Jack