Ballistic Coefficient

[Ross308]

Got two questions that are maybe a little related. I've been going to try the Sierra 135 gr. HPBT match bullets. Have any of you .308 shooters tried this wt. yet and if so with any luck? Anyway, when I was comparing the ballistics of various Sierra rounds for the .308 I checked out the 155 gr. HPBT Palma as compared to the 155 gr. HPBT Match ammo. Same wt. and sectional density but different coefficient. The Palma shoots great and so does the Plain HPBT. Got no complaint on the accuracy of either one but would like to know where the difference is.
Thanks for any light on the subject.
Dan R.

 

[RonAKA]

Sectional Density just depends on the weight and bore. BC is a measure of drag resistance, and is significantly affected by the shape of the bullet. The Palma bullet is longer and more streamlined, so has less drag and higher BC. It will require more spin to keep it stable. See this link:

http://www.sierrabullets.com/index.cfm?section=new_products&page=2009

 

[Ross308]

Thanks for the quick reply. I couldn't see the difference visually but the link you provided cleared it up for me. A lot to this ballistic stuff and I'm pretty sure some of it will stay a mystery. Thanks again.
Dan R.