by B.B. Pelletier

We have discussed bulk-fill CO2 guns several times in this blog. It’s time to talk about how they are filled. Last week, we got a question about this from Jim. Since the answer is not straightforward, I thought it was time to talk about it in some detail.


My 10-meter target pistol runs on bulk CO2 or powerlets. I have set it up for bulk-fill. Gas is stored in the grip.

Meet my 10-meter pistol
My 10-meter pistol is powered by CO2 and can use either 12-gram powerlets of bulk CO2. I have been running it on bulk gas from the beginning – about seven years. I find the bulk method gives me more control over the fill, so I know when it’s time to top off. The importance of knowing the status of a CO2 fill is crucial in a match.

Since few CO2 target pistols have a means of displaying the fill status (how many shots remain), controlling the fill is very important for a competitor. The one time my gun failed me was during an important regional match, when my pistol’s bulk tank was running low and did not give me the fill I had anticipated. I shot a perfectly held 10 that dropped to a 6 (just below the bottom of the bull at 6 o’clock) because of decreasing gas pressure. The four lost points dropped me from the standings in my class (top three places) to fourth place. My type of gun does not have a removable bulk tank like the top-quality target pistols. Instead, my gun is filled in a smaller fixed reservoir by a separate small bulk tank.

Bulk fill as a cost-saver!
Even though my story sounds negative, it illustrates that bulk filling is a method of precisely controlling your CO2 gun. But it’s more than that. It’s also much cheaper. I can bulk-fill a gun for a nickel and get the same number of powerful shots that someone else gets from a 50-cent powerlet. If you shoot gas guns a lot, bulk-filling is the best way to go. Gas-guzzlers, such as the Farco air shotgun (which drinks 2.5 oz. of gas for 20 shots), have to use bulk gas. A CO2 powerlet would only last for one powerful shot with a gun like that.


The red 20-lb. CO2 tank started out as a fire extinguisher. It’s slightly shorter and fatter than the yellow 80 cubic-foot scuba tank to the left.

How do you get set up to bulk-fill?
You need a bulk gas tank. I own three 20-lb. CO2 tanks and one 5-lb. tank that is more portable. The twenty-pounders are similar in size to an 80 cubic-foot scuba tank. They start out life as fire extinguishers and soda fountain gas tanks. They are easy to acquire, though you won’t find them at Wal-Mart. Consult your yellow pages for the nearest industrial gas supplier or restaurant supply house. The industrial gas place will probably also fill the tank for you and do any maintenance you need.

Gas tank requirements
Like scuba tanks, CO2 tanks have to be hydrostatically tested every five years. As a huge user of CO2 10 years ago, I used to consume the contents of a 20-lb. tank in about two years. Calculating the shots I got for a Crosman 111 pistol, one 20-lb. tank provided almost 30,000 shots for $14. That was eight years ago, and the cost of gas has no doubt risen since then. I have purchased two additional tanks in the meantime, both filled, so it’s been that long since I went back to the gas supplier for a refill. A scuba tank holding air may give 2,500 to 3,000 shots per $3 fill in an equivalent air pistol, so both gasses are relatively inexpensive.


A tank needs a siphon tube to draw the liquid CO2 from the bottom.

Bulk tank needs a siphon tube.
Since you want liquid CO2 to come out of the big bulk tank, there has to be a siphon tube inside. It reaches down from the outlet valve to the bottom of the tank. The CO2 gas in the tank pushes down on the liquid, forcing it up the tube and into whatever you connect to the tank. Without the siphon tube, you would have to hold the CO2 bulk tank upside down to force the liquid out first. As heavy as the tank is, you don’t want to do that!

Are large CO2 tanks safe around the house?
Since the other name for CO2 tanks is fire extinguishers, they’re not only safe, they ought to be in every home. Once when some kids abandoned a stolen car in front of my house because the engine was on fire, I put the fire out with one of my bulk tanks. So, yes, they are safe. Just store them where they cannot fall and damage the valves.

Tomorrow, we’ll look at how the CO2 moves from the bulk tank to a smaller tank or the gun, itself.