Lyman manual deffinition

[deadeye dick]

Just finished reading the 49th Lyman manual. on the loading specs. next to the bullet type there is another spec. It says BC: than a number and under that SD: and a # Can't find anything on those two abbreviations. Any help?
Thanks Howie

 

[243winxb]

Sectional Density Ballistic Coefficients https://www.sierrabullets.com/store/product.cfm/sn/1530/243-dia-6mm--85-gr-HPBT

 

[KansasSasquatch]

As pointed out above BC stand for ballistic coefficient. SD is sectional density. Bullets with higher ballistic coefficients are more aerodynamic than same caliber bullets with lower BC's, given that the two bullets are equal weight. They'll tend to shoot flatter trajectories. Bullets with high SD tend to penetrate further, unless designed to expand. These links might help you http://www.chuckhawks.com/sd_beginners.htm http://www.chuckhawks.com/bc.htm