A GUIDE TO CO2 CYLINDERS
Written by: Joseph Mucelli
The most common CO2 Sporter air rifle used in competition is the Avanti M888 or “Medalist”,
manufactured by Daisy. The following information refers to the use of the detachable cylinder
as used in that rifle only. In addition to the basic rifle with cylinder, it is necessary to purchase
three additional items: a master cylinder, a Daisy “fill adapter” and an accurate digital postal
scale.
A master cylinder, usually with a 20 pound capacity, and equipped with an “eductor tube” is the
source for refilling the rifle cylinders. Dealers for master cylinders can be found by looking in
the Yellow Pages under “gas”. A 20 pound cylinder costs around $100.00, but some
companies will provide a cylinder at no charge provided that you use them for refills. Average
cost of a 20 pound refill is about $25.00. The eductor tube permits filling with liquid CO2 from
the bottom of the tank, which is essential because of the limited capacity of the rifle cylinders.
The next item necessary for use of 888 rifles is a Daisy “fill adapter”, which is used to connect
the master cylinder to the rifle cylinder.
The final essential item is an accurate digital postal scale. A scale is necessary because CO2
cylinders do not have pressure gauges. Since CO2 pressure varies with ambient temperature
the only way to accurately determine correct fill is by weight rather than by volume. Since the
888 cylinder is designed to function correctly with 2.5 ounces of CO2, it is necessary to weigh
the empty rifle cylinder and then fill it to 2.5 ounces over the empty weight. The average 888
cylinder weighs 14.2 ounces empty, therefore the ideal filled weight would be 16.7 ounces.
Since manufacturing tolerances may vary, it is important to weigh each empty cylinder.
A full cylinder can be relied upon to be good for approximately 100 shots. An overfilled
cylinder will result in lower, variable, velocities as the rifle’s valve tapping system will be unable
to overcome the excess back pressure. Overfilling can also cause the “burst disk assembly”,
an over pressure system, to open, which will make the cylinder unusable. This can also
happen to correctly filled cylinders if left in a car or in direct sunlight in extremely hot
conditions! If this ever happens while you are driving it will almost instantly white out all the car
windows!
To fill a cylinder it is wise to chill or freeze the rifle cylinder(s) and the fill adapter. At matches I
usually place the cylinders and fill adapter in a waterproof plastic bag, and keep them in an ice
filled insulated chest. Without a means of chilling these items it is necessary to go through a
process of filling and bleeding off CO2 until they are frosted. Without pre-chilling, or bleeding
off CO2 , it is almost impossible to get a full 2.5 ounces in the cylinders! If you have to use a
master cylinder without an eductor tube it will be necessary to hold the cylinder upside down
over the rifle’s cylinder. Rifle cylinders should be permitted to return to ambient temperature
before you start firing, otherwise you will get constant elevation changes as the temperature
increases! The step by step procedure for filling a cylinder is as follows: (Use the diagram of
the Daisy fill adapter as a reference)
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1. Make sure there is a washer in the tank end of the fill adapter, and wrench tighten it to
the master cylinder.
2. Close the bleeder valve knob.
3. Visually check the neoprene gasket on the rifle cylinder. If it is in any way damaged,
replace it! Spares are available at paintball shops or at Walmart.
4. Screw the rifle cylinder into the end of the fill adapter and hand tighten it. Then screw
in the knob to open the valve on the rifle cylinder.
5. Open the valve system on the master tank. If you have never done this before, open
the master tank valve for only a few seconds. Experience will tell you how long to keep
it open.
6. Close the master tank valve.
7. Unscrew the knob on the rifle cylinder end of the fill adapter to permit the valve system
to close.
8. Open the bleeder valve knob on the fill adapter to release residual CO2 in the system.
9. Remove the rifle cylinder from the fill adapter. Usually you can remove it by hand, but if
you have overfilled the cylinder it may be necessary to use slip joint pliers wrapped
around cloth to release it.
10. Weigh the filled cylinder. It should be as close as possible to 2.5 ounces over the
weight of the empty cylinder. If it is higher, bleed it off by pressing on the pin in the
center of the valve with a blunt metallic object like the handle of a wrench. If it is lower,
repeat the fill procedure. Remember, liquid CO2 is very cold, so avoid skin damage by
using gloves.
To place the cylinder in the rifle, it is necessary to carefully hand screw it in as far as possible
and then to use a wrench to tighten it until it just bottoms out. It is best to “choke up” on the
wrench close to the cylinder to avoid over tightening. Over tightening the cylinder will
eventually result in pulling out the entire valve system the next time you remove it!
When traveling by air with CO2 rifles, it is necessary to empty all cylinders and preferably
remove them from the rifle. Some coaches have experienced difficulty in transporting CO2
cylinders because security personnel will not accept the fact that the cylinders are empty even
when it was demonstrated that no CO2 came out when the valve system was pressed in. They
were looking for a pressure gauge. In one case security personnel required a coach to
unscrew the small hex head at the end of the cylinder which is the over pressure “burst disk
assembly”. This destroys the cylinder! One successful method of avoiding problems has been
to use a label program and make labels stating “this cylinder certified empty”, signing them,
and sticking them on your cylinders! If you are going to matches it is also a good idea to have
extra cylinders!
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DAISY FILLER ADAPTER
FOR M888
KNOB TO
BLEED FILLER
ADAPTER
KNOB TO
OPEN RIFLE
CYLINDER
VALVE
CONNECTION
TO MASTER
CYLINDER
CONNECTION
FOR RIFLE
CYLINDER
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