Joules, Joule Creep and HPA Chronoing Explained
I think most people have some understanding of what Joules are and how they
are used in airsoft. If not, Joules are a measure of energy that a BB has after
it is fired. (As opposed to FPS, which is merely a measure of the velocity of a
BB, ignoring factors such as the mass of the BB itself). To further illustrate
the difference between Joules and FPS I will give an example of both. FPS is
only a measure of the velocity of a bb, which means no matter how big, small,
massive or tiny the bb is, FPS will not be changed. If it is traveling at
400FPS, that is that. No other factor affects FPS apart from the speed of the
projectile. Now, Joules is calculated differently. Joules is a measure of
Kinetic energy (in terms of an airsoft bb) and can roughly be calculated by:
((mass)•(Velocity^2))/2. Here is an example: (.0002kg • 100m/s^2)/2 = 1J. This
means a .2g bb fired at 100m/s carries 1J of energy. Joules are a superior way
of measuring energy of a BB because, well, they actually measure energy. Joules
takes into account more than just FPS, it factors in the mass of the bb as
well.
Now that we have developed a basic understanding of what Joules are used for
in airsoft, lets investigate some inaccuracies throughout the airsoft community
about Joules. We will start the domino affect with (quoting Thomas Grace): "BB
weight does not effect the Joule rating of a BB. This is a FACT!!" This
statement actually cannot be more false, since BB weight is precisely the reason
why Joules differ from FPS, in terms of airsoft. This statement was followed
with a correct explanation of what joules are in the source writeup I am quoting
from, so l will assume he simply mistyped. However for everyone reading his (or
similar) write ups this needs to be brought to attention. I will even use his
own joule chart:
.20g BB 400 FPS 1.48 Joules<BR> .25g BB 360 FPS 1.48 Joules<BR> .28g BB 337
FPS 1.48 Joules
Now, if we make the variable joules rather than FPS, this is what the chart
looks like:
.20g BB 400 FPS 1.48 Joules<BR> .25g BB 400 FPS 1.86 Joules<BR> .28g BB 400
FPS 2.09 Joules
<P> As you can see, bb weight does affect Joules. I know it seems
counterintuitive to even question this after defining Joules the way we did, but
some things need to be "proven" outside of a definition/equation. The argument
against this, and why it needs to be "proven" is: "but in the same setup, a gun
will shoot 400fps with .20g, 360fps with .25g and 337fps with .28g and so on.
So it will always shoot 1.48 Joules regardless of bb weight." Sadly, this is
simply false due to a term properly titled "Joule creep". And, no, Joule creep
is not a myth, it is physics. It is important to know that most setups
(especially AEG builds) do not have significant Joule creep, but there are many
factors that contribute to achieving (or accidentally having) Joule creep in a
setup; the most important being air volume.
In all airsoft guns, you have a certain amount of air that pushes a bb down
and then out a barrel at an energy of "x" Joules.
1) If you have too little air, the bb will stop accelerating before it
leaves the barrel and you end up losing potential energy in your system.
2) If you have the perfect amount of air, your bb will accelerate throughout
the entire path inside the barrel and leave with a propper Joule rating "x".
3) If you have too much air, the bb will accelerate all the way to the end
of the barrel and leave with a Joule rating of "x" just like with the perfect
amount of air, but this time you still have excess air in the barrel. This air
gets wasted since it dissipates after the bb is shot out. Sometimes it also
creates a negative effect on the bb slightly lowering the energy output and
possibly accuracy.
Now, lets apply the above variables of bb weight to these three situations.
We know from basic science that heavier things accelerate slower (F=MA). So, if
we take the over volumed setup that was still getting a Joule rating of "x" but
wasting air, and we throw in a heavier bb, the heavier bb will accelerate slower
(F=MA) which means it will stay accelerating in the barrel longer, using up some
of that extra air resulting in a higher Joule output. The reason I bring this up
is because, while Joule creep isn't as prevalent in AEGs with cylinders that
restrict the maximum volume of air, it is much more common in HPA (or even GBBR)
setups due to the abundance of air/gas volume coming from your tank (or gas
reservoir).
This means that, with a P* FE for example, you can purposely (or
accidentally) over volume your system so that it shoots 400fps with a .20 BB but
wastes a lot of air after the bb leaves the barrel. Because it is wasting air
with a .2g BB, a .3g BB might make the setup still shoot 380fps (for example)
since the .3g bb accelerates slower than the .2g BB and uses more of that wasted
air. This results in a higher Joule output with the heavier BB at the exact
same air pressure setting (psi). This also means that if a field makes
everybody chrono with .2g BBs that player would have clocked in at 400fps and
1.48joules, right on the money. But out on the field when he is playing with
his .3g BBs (not the field provided .2s for chrono) he would clock in at 1.98
Joules, a significant increase. (1.98 Joules is roughly 465fps with .2g BBs for
your reference, so he is now 65fps above the field limit but he didn't change
his regulator settings at all).
Here is a different write up l made a while back, however it was specific to
HPA based platforms:
"Ban HPA?
In my opinion, if banning an entire system is your way of "fixing the
problem", then you have a seriously flawed mentality of the actual problem and
took very limited time to sort out a real fix for this issue.
There are many ways to logically fix the problem of users abusing an item
(in this case HPA powered airsoft guns) and still allow the honest users to
continue using this item.
1. Chrono by Joules with both the bb and barrel that the player will use on
the field. FPS is just a function of energy, Joules are the actual energy
output. With HPA guns there are three ways to increase the joules of the gun.
Use heavier BBs, lengthen the barrel (also simply increasing barrel volume in
P*) or adjust the regulator/FCU settings. In P* and V12 systems you can also
swap nozzles. That's it. Regulate those 4 things while chronoing and you
cannot possibly have people upping their FPS/Joules without breaking field
chrono rules.
2. Make tournament locks mandatory on air rigs/regulators and FCUs. This is
common sense, any field owner that does not practice this is just dumb to be
honest.
3. If you want an RPS limit, have an RPS limit for ALL setups. I have 3
AEGs that shoot faster than my SMP setup's max rof setting. Any system can get
to a high rof, regulate them all so that, in the end, the energy output has the
same cap.
4. Actually enforce these rules in staging, during the chrono and while the
game is going on. Strictly adhere to HPA users not being able to swap in a
longer barrel or heavier bbs without re-chronoing. Make sure they all have
tourney locks on their FCU and regulator. Having the rules is one thing,
enforcing them weeds out the cheaters and creates a harmless environment.
Because, lets be honest, rules are made to be adhered to. To guide users to a
safe and fun experience. The whole point of rules is to keep things both safe
and enjoyable, their main purpose is to get rid of the players making the
experience less safe or fun for the majority.
5. Have referees with hand-held chronos. Xcortechs are great. If somebody
is suspected of cheating with an HPA system (or any system, really) spot check
them. If they are above the joule limit or RPS limit set by the field that
means they had to have changed their BBs, barrel or system after chrono and are
breaking rules.
6. Kick these cheaters out, repeat offenders should be banned. Just like
with any other situation violating the rules. That is the while reason for
having rules in the first place. People that abide by them can stay, people
that don't have to go. The person does the cheating, the gun doesn't know the
rules let lone have the ability to break them.
7. EDUCATE HPA users as part of the standard safety briefing BEFORE all
games. (Point brought up by Kory Escue) Make sure they know what their system
is capable of and that changing something as little as BB weight or barrel
length can affect the Joule output and be against the rules. This way,
ignorance to your system is not an excuse for either cheating or simply using
heavier bbs your buddy gave you after you chrono because he said they would fly
farther. This way, nobody using an HPA system "doesn't know" what the
restrictions around his system are and how he/she can break them.
If you have these rules set in place the people not breaking them will be
harm free, as they will never chrono above the joule limit when being spot
checked. Every person who adheres to these rules will enter a safe and fun
environment. This will result in the overall name of HPA not being slandered as
well as a harmless environment and fun day of airsoft all around. The people
not adhering to these rules are the problem, ruining the game. As long as you
follow all of these steps, the rule breakers will not have an excuse and can be
punished.
Also, FPS cheating happens with AEGs that are over volumed or have a high
bop setting during chrono as well. Or systema systems with their cylinders.
Sadly, there have always been and always will be cheaters. The refs who spot
check you will compare to how you chronoed initially. If they take your own mag
with your own bbs you have been using and chrono it above joule limits, then you
will be labeled a cheater and kicked out of the field since you must have
changed something from when you initially chronoed, solving the problem.
(Again, this works when you chrono by Joules AND follow all of the above steps).
Think about it, if you follow the above rules I laid out, you wouldn't even be
allowed on the field unless you chronoed within the field's Joule limits
initially and with the system you were going to run. If you are all of a sudden
spot checked at above the Joule limit, you MUST have changed something in your
setup. This is the whole point of having any of these rules in the first place,
to catch the cheaters.
Follow these rules and you will have games where it is IMPOSSIBLE for HPA
users to be shooting at a higher energy output or higher RPS unless they went
against the rules, that they were aware of, and deliberately changed their own
system after chrono. This proof allows you to ban the cheaters and keep the
honest players, which will eventually get rid of the problem, just like any
other situation where cheating is involved.