Quote:
Originally Posted by Grizzly Adams
The part that confuses me is how they derive that snake oil  input that quantifies the bullet's profile., what Hatcher calls the form factor.
Grizz |
Using the word "factor" sounds a bit confusing alright. i.e. what IS a 'factor'?
It can also be thought of as form "drag", a force acting against the bullet's energy. The form(shape)of a bullet directly affects it's efficiency. i.e. a ball and a bullet might have the same sectional density, but the shape(form) of the bullet makes it more slippery through the air and thus has a greater BC. This diagram might help:
http://www.centennialofflight.gov/es...drag/TH4G2.htm
Hatcher is very correct when he states that the form "factor" changes with velocity i.e. transonic, sub and super sonic. Airplane designers had all sorts of problems with this prior to supersonic flight. A wing would build up a pressure wave of compressed air ahead of it as speed increased. When the speed of the wing reached transonic values and began to overtake the pressure wave, the air flowing over the wing would become turbulent and adversely affect the control surfaces on the trailing edge. Eventually they realized that by designing a swept back wing, so that the wing did not go trans/super sonic all at once, it dramatically improved control and stability until all of the wing was going super sonic. Then they looked more at things like "form", or shape, to extend the distance the air would pass smoothly(laminar airflow) over the wing, thereby making it more "slippery"(less drag) and improving it's BALLISTIC COEFFICIENT, if you will.
For some calibres, using copper as opposed to lead will increase the BC because for the same mass/weight more can be done to optimize the form/shape of the bullet. If you look at manufacturer's charts, you can see that, generally, the high BC bullets carry more "thump" downrange.
I hope my analogous references to airplane wings helps.
Cheers,
