Airgun World – July 2019

http://www.airgunshooting.co.uk AIRGUN WORLD 75

UP IN THE AIR

T

he science of projectiles in flight is called
‘external ballistics’, and it is a subject I
normally shy away from because it
encompasses areas of physics that are close
to impossible for the layman to comprehend,
and much of the subject defies explanation by
way of simplification. The great problem is
that some people have written about it, and
HAVE attempt to over-simplify it, often using
flawed analogies, with the result that a lot of
what has been written on the subject, and is
contained in videos available on the Internet,
is plain wrong.
I was fortunate enough to be approached

TECHNICAL AIRGUN

Jim looks at how on earth our tiny lead pellets manage to hit distant targets

»

last year by retired ballistician, Miles Morris,

who was keen for me to publish an article that

set the record straight, which meant that

between us we first had to educate me (no

small task). Three months on, with much help

from Miles, and many hours studying the

NASA and Hyperphysics educational web sites,

I feel ready to give it a go.

OVERVIEW

Ideally, the pellet would point in its direction of

travel throughout its flight from the muzzle to

the target, although for a number of reasons,

the pellet won’t constantly be pointing quite in

its direction of travel, and the difference

between its direction of travel and the direction

in which it is pointing is called ‘yaw’. Yaw can

cause the pellet to deviate from its intended

trajectory, and the potential ill effects from yaw

are mitigated by the mechanisms of stability.

The waisted, or diabolo, pellet shot from an

air rifle benefits from three types of stability

that help to keep it on course to the target,

and these are; spin, aerodynamic and

dynamic stability. In order for the pellet to

stand any chance of hitting the desired pellet

point of impact (POI), all three forms of

stability must contribute; two out of three

It’s incredible that a tiny 8.4 grain lump of lead can travel 40 yards at high speed and land where it was intended to land.