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First, a disclaimer. This review and article deals in part
with the chemical composition of gases. I am not a chemist. My fields of study
are computer science and 20th century geopolitics, with a fair understanding
of Newtonian mechanics. However, I did take a bit of chemistry in high school,
which is hazy enough to be only partially useful, and I worked at the nanotech
lab at the University of Texas at Dallas this summer, where I brushed up on
the elementary basics of organic chemistry, which are unrelated enough to be
mostly irrelevant. However, I should be as qualified to judge the data presented
as the typical airsoft player, and vice-versa. I can give my view of presented
conclusions, but you should also make your own decisions. That is, tread carefully
since the article deals with some ideas fairly radically new to the mainstream.
-Shane "Supergeek" Lin
(Click for full size image)
Of the three general types of airsoft guns, those
that are powered by gas clearly produce the best sense of realism. The operation
of the cycling bolt or slide cannot be easily replicated by either an electric
motor or a manually compressed spring. That is, it is difficult to generate
the requisite torque with a small enough motor and battery and using a spring
to cycle itself sort of violates the laws of thermodynamics. However, also unlike
electric and spring, renewable respectively through rechargeable batteries and
the human consumption of food, gas guns must be satiated by a continuous supply
of airsoft gas. For the modern GBB, this typically means made-for-airsoft HFC134
or green gas. Although PC Duster gas can be substituted for HFC134, the jury-rigging
required to create a viable nozzle makes the process less than healthy for fill
valve o-rings. Thus, the discovery of a very low-cost, high availability gas
would certainly be a sort of airsoft holy grail.
It was some weeks ago when my boss, Big Aaron Benzick,
dropped off a production model of an adapter nozzle for small propane tanks
made by the newly start-up Airsoft Innovations. The use of propane to cycle
gas blow-back pistols as an alternative to Green Gas is not unprecedented. In
fact, some players have been reportedly using it for years with success. However,
it has never quite hit mainstream, being relegated to the experimental fringe
with other gases (like Butane, which can be habit-forming and cause serious
health issues if inhaled). This is the first commercial product to my knowledge
which adapts propane for airsoft purposes.
Cost Benefits
Propane is highly economical as an airsoft gas. I picked
up a small can of Coleman Propane Fuel, probably designed for gas lamps and
small cooking grills, from the local Target for around $2.50. The net mass is
465g, so given a density of around 583.074kg/m^3, the can contains about 7.97x10^-4
cubic meters of propane. So, the cost if $2.50 for just under 800ml of airsoft
gas, which makes propane about 3 times less expensive than the cheapest airsoft
green gas I could find in the United States. And you don’t even have to
have it shipped to you. Apparently, in Canada, obtaining green gas is much more
expensive than in the US, which would mean an even greater ratio.
So, for the average US airsoft player, the best price
for a 1 liter can of green gas will probably be around $9-$12 with shipping.
The Airsoft Innovations adapter nozzle is being sold for $30 USD shipped. Propane
is around $2.50 for a 800ml can. Throw in $3 for a bottle of silicone oil, which
will need to be added to the magazine before using propane. Which means (and
I’ve done the math for you here already), the adapter covers its own cost
after 6 cans of green gas, assuming the cost of $9. I’ve certainly used
more than that in the past few months.
The Adapter Nozzle
I am really fairly impressed by the unit itself. It
is made of very nicely machined brass and is composed of four pieces. There
is a large threaded fitting that screws onto the propane tank, a washer and
spring which go into the fitting, and the nozzle, which is inserted last. The
four-piece design seems to be to ensure the widest compatibility with various
propane tanks, as well as to allow easy removal of just the nozzle to ensure
safe transport.
Installation is completely inconsequential. A very smart
monkey could assemble it in around 15 seconds. Since it may equivalently take
the average airsoft player upwards of a minute to figure it out, I’ve
included a quick video demonstration, omitting only the step about placing a
drop of silicone oil on the nozzle (I’d just done that right before),
Check the media section at the bottom for the video.
Along with the nozzle, I received a very nicely illustrated
manual documenting installation and use, as well as some hazards and precautions.
And a stereotypical Asian woman without a nose. But, being a fellow Mongoloid
(big M, not small), I wholeheartedly approve. In fact, the illustrations are
very good, and the whole production is really much better than I could have
expected from something like this (especially after wading through all those
little colored paper strips that come with Japanese aftermarket accessories
and upgrade parts).
The nozzle seems to provide as good of a fit as any
green gas bottle when it comes to filling. I don’t have a KJW or HFC magazine
on hand to really test it, but I’m sure that it’ll achieve the same
no-leak seal with those guns as the typical green gas bottle. Oh the whole,
it offers a much less leaking than hand-cut plastic nozzle adapters using duster
gas. It is also long enough to reach into the fill valve inside the bumper pad
of my Western Arms V12, a gun which has had problems fitting various other gas
bottles in the past.
Green gas = Propane? That’s crazy talk!
Carlton Chong, the Canadian mechanical engineer behind
Airsoft Innovations, goes further to claim that at the least many brands of
green gas often used for airsoft purposes are actually just propane. While this
may at first seem incongruous with everything which you’ve been told about
green gas, with some thought it makes a lot of sense. I have a bottle of green
gas here. It is the green-and-white camo pattern kind marked “Green Gas
- Super Power” which is very common in the United States. On it is a label
declaring that its chemical composition is CH2 FCF3 CH3, which is also listed
as the chemical composition for other brands. This sounds reasonable, as the
less mysterious HFC-134 and Propane gases are well documented (because of their
refrigeration and cooking utility) and are composed of, respectively, CHF2CHF2
and C3H8. Clearly, CH2 FCF3 CH3 (green gas) is not equivalent to C3H8 (propane).
What’s wrong here, then? As Carlton points out,
CH2FCF3CH3 doesn’t actually exist (for a marketable amount of time, at
least). And he’s right. Under octet rule, such a molecule would be unstable
because carbon does not have enough bond sites for all the Hydrogen and Fluorine.
Even with my lack of education in deeper matters, this much is certainly crystal
clear.
So, I corresponded with Carlton to find out the specifics
of his tests. It would seem that he’s been quite thorough. He writes of
conducting three tests himself with Coleman propane and at least three types
of green gas: Jet Gas, “Shooting Air” and “Green Power”.
He compared the flames of the various green gases with the propane and tested
for pressure at various temperatures and the density at room temperature. All
tests were successful to degrees of relative certainty. Let’s take a look
at the tests. The flame test is a good test for exclusion since some gases produce
vastly contrasting flame colors. That the flames were similar is not an indication
that the tested gases are the same, since dissimilar gases can also produce
comparable flame colors. There’s a video of this test on the Airsoft Innovations
article on his tests – it’s pretty darn cool. By testing for pressure,
I think that he’s measuring the saturated vapor pressure of the gases
are various temperatures. That is, for a specific substance at a given temperature,
the saturated vapor pressure is the pressure at which the vapor of that substance
is in equilibrium with the liquid. Density is mass over volume, so figuring
that out wouldn’t be very hard at all. However, I don’t think that
density tells us so much, since oderants and lubricants must be considered,
not to mention that many things may have similar density. For instance, Ethane
(C2H6) is only 2% less dense than propane, which was the same limits of the
difference measured between the green gas and propane. But I’m being a
little unfair. The various comon chemicals which share similar properties have
more tangibly different densities. Butane, for instance, is somewhat more than
2% more dense, while HFC-134 (unless I’m horribly miscalculating) is more
than twice as dense. The vapor pressure test is more revealing and helpful in
arguing that the tested green gas and propane are one and the same, I think.
However, it contradicts some of my practical experimentation. We’ll get
to that in a bit.
The icing on the cake though, is the result from tests
run on the GC-MS. Carlton has apparently sent in samples of various green gases
to be analysed by at Analest Laboratory at the University of Toronto on their
gas chromatograph / mass spectrometer. This is now totally out of my field,
since the best I can claim is to have been about 3 feet away from one of these
at UTD. The Airsoft Innovations site has a good explanation of it, which will
be much better than I could do. I also can’t really comment on the validity
of the results further than the standard “oh, those graphs look really
similar!” Just in case anyone was wondering, I do know that GC-MS is a
legitimate scientific instrument which typically produces good results. I can
understand that to someone who knows how to read a chromatogram, these results
could probably instill a high degree of confidence.
There has been an unsubstantiated internet claim that
“green gas” is actually a fluoropropene rather than straight propane.
This claim was found without justification, but I believe that it may have validity.
I talked with my local chemistry PhD and verified that it is possible that with
the additional fluorine atoms, the final gas would be somewhat less flammable
or produce slightly different pressures. However, Carlton’s argument that
since the green gas has already certainly been misrepresented there seems to
seems to be little incentive to use a more expensive fluoropropene rather than
straight vanilla propane is difficult to argue with. For the time being, I would
think this claim to be somewhat specious.
Performance
Well, how does it shoot? The answer seems to be: great!
It was late at night when my friend James and I got back with the propane. Since,
we wanted to prepare for any possibility (i.e. my bursting into flames and running
about as a human torch), we locked his dogs (see picture) inside the house and
readied the fire extinguisher. Installation took the requisite 15 seconds, and
then we were ready to go. I used one of my KSC Glock 19s for this first run,
since it was equipped with a metal slide. Results were highly satisfactory.
In fact, I felt that the propane was producing greater blowback than my green-and-white
camo green gas. I was using the one G19 mag whose fill valve leaked slightly
with green gas. With propane, the leak was tangibly greater. I noticed the same
with my G26 short mag. This goes to indicate that the propane perhaps produces
more pressure. Without a chronograph, I could not measure muzzle velocity, but
results from coke can tests were similar to those with green gas. The propane
also seems more resilient to the effects of cooldown when compared with green
gas. However, the differences in these characteristics can probably be attributed
to differences in purity, odorants, and lubricants.
Conclusion
With all the available evidence presented on the Airsoft
Innovations site as well as my own experimentation and email discussions with
Carlton, I cannot really find fault in his assertion that many green gases are,
in fact, simply propane. I believe that he is right.
Given this caveat, the green gas adapter is simply an evolutionary step for
the western GBB enthusiast community. The sudden availability this alternative
power source is certain to expand the accessibility of gas guns by a significant
margin. I would highly recommend it.
Disclaimer #2
Propane is highly flammable. I mean, it’s propane. The Coleman MSDS sheet
for propane lists it as the highest of 4 levels of flammability - “Extreme.”
So, don’t smoke while you’re filling up. Propane is also a simple
asphyxiant. Clearly, don’t have 8 people at a time filling up their entire
gas gun collection inside a parked car with the windows rolled up. And of course,
it’ll cause frostbite with prolonged skin contact. And don’t get
it in your eyes. All this is of course the same as with regular green gas. On
the plus side, you can't really accidently injest it. And it doesn't cause cancer
(at least not very quickly).
Additional Materials
Links
Airsoft-Innovations.com
AI
article documenting green gas / propane testing
Material Safety Data Sheets (MSDS)
In any chemistry lab, you should be able to find a collection of MSDS sheets
containing one for just about every chemical that can be expected to be encountered.
This sheet typically has important chemical and physical properties, as well
as warnings and immediate protocol in the event of an accident (eye/skin contact,
injestion, etc). Here are two MSDS sheets from Coleman and Shell on their Propane.
Coleman/Ferrellgas Propane MSDS
Shell Canada Ltd. Propane MSDS
Also, I've some videos in MPEG format ("right click/save target as"
to save):
Fill.mpg - Filling a Glock 19 magazine for the first
time with propane - 4.73MB
Install.mpg - Installing the adapter nozzle onto a
Coleman propane tank - 5.6MB
G19.mpg - Shooting the KSC Glock 19 with propane - 3.99MB
Beretta.mpg - Shooting the KSC Beretta M9 with propane (from a mostly empty mag)
- 5.36MB
Kudos to anyone who recognizes the painting behind me.
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