Forgive me, I'm going to
cover the basics and then move on to, so if you are an experianced airsofter
you'll already know a lot of this.
FPS stands for Feet Per
Second, for those of you who hate anything other than SI units (Systeme
Internationale), one fps is 0.304 meters/sec, (equivalently 1m/s = 3.28 fps).
This is why 328fps is thrown around as a limit. 328fps is 100m/s, and a 0.2g
bb travelling at this speed possess the energy of exactly 1 Joule.
(in joules) = 1/2 mass * velovity^2
can I calculate my airsoft replica's energy?
handy form I have created for you below, you can calculate your replica's energy
in joules. As a by-product it'll also give you your bb's velocity in m/s. To
calculate the energy in joules, simply enter the mass of ammunition (in grams)
that you use, and the fps that you've read from your chrono unit.
The generally accepted limits
in the UK, are as shown below:
328fps (with 0.2g BB)
These are of course self
regulated, and you'll need to check with your skirmish site for what
they accept as limits.
my range? Well I've been having a think about this, and we will
be conducting some tests with some AEG's at some point in the warmer part of
the summer, from these we'll be able to deduce some real-world figures. Right
now though the easiest thing that I can do is calculate some range using basic
physics, making certain assumptions. For starters we'll ignore hop-up, as we
know it increases range, and I'm not going to sit here and work out higher level
physics using specific air density and fluid dynamics - I'll do
that later on =). This model assumes a curved flight path, I know hop-up
produces a straighter path, but you'll be suprised how close the figures
from this model match to real-life.
From basic physics, lets
start with a basic equation:
= distance u = initial velocity v = final velocity a = acceleration t = time passed
= ut + 1/2 at^2
Assume you are firing the bb from a height of 1metre (i.e. with your rifle shouldered),
lets calculate the time it takes for your bb to drop and hit the ground:
s = ut + 1/2
1 = 0 + (0.5* 9.81) * t^2
t = sqrt( 1/(0.5*9.81) )
t = sqrt(0.203...) t = 0.45 seconds (2SF)
Hence time taken to fall
1 metre is 0.45 seconds. With a velocity of 328fps or 100m/s,
this mean your bb will travel (328*0.45)=148feet or 45metres
before hitting the ground, giving you your effective range. If you don't
know the energy of your rifle, you can either calculate it above, or use 1J
as the limit for AEG's, and 2.31J as the limit for single action.