From:	Adam Getchell acgetchell@*******.edu
Subject:	Ballistics (was: Two firearms at once)
Date:	Mon, 8 Mar 1999 11:14:00 -0800

> Finally, while others have pointed out that spinning bullets
>actually do generate lift, it should also be pointed out that the
>main reason that rifles and other long arms have longer ranges because
>they can achieve much higher muzzle velocities than pistol rounds,
>sometimes by as much as a factor of 2 or 3.

As I mentioned in my earlier post, aerodynamics plays an important role,
especially in the case of rifle bullets. Rifles have superior range in part
due to greater velocity, and in part due to the design of their bullets.

Drag force can be expressed by the equation F = 1/2 *Cd*rho*A*v^2

where Cd = Coefficient of drag
rho = density of medium (e.g. air)
A = cross sectional area
v = velocity of the object

Note: this law is not valid in all regimes (i.e. it is not fundamental).

The reason for going through this equation is one can immediately see that
the bullet shape of a rifle (ie pointy, boat-tailed) serves a number of
important functions in reducing area (note rifle bullets tend to be smaller
caliber than pistols) and the Cd (which can vary significantly between
blunt tip than a sharp nose/boattail).

Coefficient of drag is a catch-all term, that tends to incorporate effects
of boundary layers at different regimes of Reynolds' numbers. (For a golf
ball, for example, the area of interest is Re20,000 to 100,000.) That is to
say, the interactions can be complicated, which is why physicists call it
fluid mechanics and engineers call it aerodynamics.

As a practical note, regardless of initial velocity all bullets tend to
drop into the subsonic regime by around 900 meters, which degrades accuracy
at that point. Not saying it can't be done, but I would tend to think
sceptically of snipers making kills beyond that range. It would seem be one
reason why the OICW went for a bursting area-munition to achieve their .3 -
.5 hit probability at 1000 meters.

P.S. Note to Paul: I did mention that diameter of the round (i.e. wound
channel) is also important in determining volume of tissue damage. Body
tissues are elastic, and there is a minimum amount of energy that needs to
be imparted to cause trauma. Small, hard (compared to the body),
fast-moving pointy objects are rather good at doing so.

>Marc

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu