Airgun World – Summer 2019

http://www.airgunshooting.co.uk AIRGUN WORLD 31

H

aving safely returned from yet another
excellent Northern Shooting Show, with
my energy and vigour renewed and thoughts
of relaxing, long hot summer days to come, I
set about organising my research schedule
and headed out into the garden for some
pellet testing.
Before we get down to business, let’s have a
quick recap on the principles of ballistics,
especially relevant in regard to this month’s
testing.
There are three types of ballistics; interior,
or what happens in the chamber and the
barrel; exterior, or what happens between the
muzzle and the target; and finally, terminal, or
what happens when the projectile arrives at
the target, and it’s the latter that continues to
fascinate us.
When examining ballistics, it can’t be
ignored that what makes a projectile pass
easily though the air, also makes it pass easily
trough the target material. Notice I’ve said
‘easily’, not ‘efficiently’, because in flight we
want the projectile to lose as little of its energy
as possible, to give us a flatter trajectory.
However, when it arrives at the target we
want it to surrender as much of that energy as
it possibly can. The thing is, the two aren’t
always mutually compatible, but there is a way
of better understanding what’s going on. We’re
going to talk about our old friends ‘sectional
density’ and ‘coefficient of form’, and how they
combine to produce a ballistic coefficient, but
rather than the lengthy, three-course meal
version, I’m going to give to you it more as a
Pot Noodle, and I promise – no maths!

1: Sectional Density
Sectional density is the relationship between
the weight of a projectile and its frontal area.
There is a mathematical equation that will help
you to determine this value, but there’ll be
none of that sort of stuff here. Let’s just say
that given a fixed velocity, heavy narrow things
are able to penetrate better than light narrow
things, or indeed heavy wide things.

2: Coefficient of form
This is the really easy one. Just think of

coefficient of form as a fancy word for ‘shape’.

I’m actually willing to bet that you already

know that pointy things move through the air

better than blunt things, in which case you’ve

already got a good grip on coefficient of form.

3: Ballistic Coefficient

Ballistic coefficient is a combination of

sectional density, and coefficient of form and

is a metric that enables us to place a value on

how well an object passes through the air.

So, we now have an understanding of BC, and

know that values range from 0 to 1 – or even

greater than 1 in extreme circumstances. For the

benefit of we airgun shooters, though, the figure

seems to hover around the 0.020 mark, and as

we’ve already established, the higher the

number, the higher the BC, and the more

efficiently the pellet is able to fly through the air.

Herein lies the problem, because the better a

pellet is able to penetrate the air, the better it is

often able to penetrate the target material.

FOUR TO SCORE

Now to this month’s testing, in which I’ll be

looking at four .177 pellets; three of them

complicated, but tasty, heavy hitters, and one

a very vanilla, average weight, domed pellet.

If you’ve been reading my articles for a

while, you’ll remember that I looked at

something very similar a while back, but that

was before the days of the R2A chronographs,

which were originally on loan from Lloyd at

Blackpool Air Rifles. I say ‘originally on loan’

because I was so impressed with them that

I’ve actually bought a pair of them now.

So, starting with the heaviest first – all .177

pellets from Pellet Perfect:

H&N Piledriver: This 9.4mm long pellet tips

the scales at 20.99gr, which is simply

mahoooosive for a .177 pellet, Granted, it is

firmly aimed at the FAC air rifle end of the

market, but if you consider its extra weight an

advantage for short-range ratting or vermin

control, it might be worth your consideration.

Next, there’s the 7.7mm long, 16.02gr JSB

Exact Beast. The Beast is a good 5gr lighter

than the Piledriver, and unlike the Piledriver’s

boat-tail form, has a more traditional waisted

pellet, with a skirt.

Third on the list is the H&N Rabbit Magnum

Power. This 16.05gr lead pellet weighs only a

little less than the JSB Exact, and like the

Beast is of an elongated diabolo shape. The

Gary Wain offers an easily-digestible discourse on ballistic coefficient

PELLET TESTING - BALLISTIC COEFFICIENT

»

Cooked to perfection, and ready for testing.

With the sun shining, I was able to get out into the open.