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Sectional Density mono verses jacketed lead

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23 July 2002, 08:08
<Zingela>
Sectional Density mono verses jacketed lead
Can anyone tell me firstly does the length of the bullet make a difference to the sectional density or not. In other words would a monolythic(spelling?) bullet of 300gr in 375 have a different SD than a 300gr jacketed bullet in 375?

Secondly can anyone tell me how to work out the Bullet co-effecient as I cannot find the therum anywhere. not even on http://www.realguns.com/index.htm .

Thanks.
23 July 2002, 08:15
<Kimmo E>
No they have the same SD. The same mass per square inch.
23 July 2002, 09:08
<eldeguello>
The form of a bullet is one of the factors determining ballistic coeeficient, but not SD. SD is dependent upon DIAMETER and WEIGHT only!!
23 July 2002, 09:41
R-WEST
quote:
Secondly can anyone tell me how to work out the Bullet co-effecient as I cannot find the therum anywhere.
Ballistic Coefficient (?) BC is a number (usually pretty overinflated) assigned to the bullet by the manufacturer and relates to the bullet's efficiency, or inefficiency, at retaining velocity. Actual BC, which usually varies pretty much from the mfr's numbers, is calculated by time of flight at known ranges, as long as the muzzle velocity is known. I'm over my head with BC, but I do know that BC's are theoretical and vary with velocity. There was a thread running in here a few months ago about it. Maybe a search will turn something up for you.

R-WEST
23 July 2002, 14:48
Ray, Alaska
Maybe you can find some answers here:
http://internet.cybermesa.com/~jbm/ballistics/secdens.html

Or here:
http://www.molonlabe.net/johns/bcmain.htm
24 July 2002, 18:48
waitaminit
The two components of BC are Sectional Density (SD)and Form Factor (i), where SD is a function of dimension and weight of the bullet. The performance of the bullet as expressed by the BC is calculated by applying i on SD where incorporates form of bullet (most importanz part of the factor), material of bullet, lubrication (moly...) and other factors I do not remember.

You may have a look at Hatcher's Handbook where he discribes how to calculate the BC. Here you'll find silhouettes of bullet shape for evaluating i.