Working with bulk-fill CO2 guns

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.

29 thoughts on “Working with bulk-fill CO2 guns”

  1. Hello BB,

    I have seen a Website where a guy build a siphon tube in his vertical gas reservoir of his gun. Like any guy of stage 3 he said nothing about accuracy. He called it “Liquid Power” because he got the same increase of power as with the first shots of a gun with horizontal tank you discribed last week. Do you think this is a good idea or just a waste of gas?


  2. Markus,

    I think the idea is a waste of gas. The best way to get more power from a CO2 gun is to open the ports through the valve and decrease the valve closing spring tension, plus increase the barrel length.

    I once read about a gun called CO2Much that shoots a 7.2-ounce lead slug at about 400 f.p.s., developing about 1,000 foot-pounds. But it can’t hit anything. If we could launch a bowling ball with CO2, it would be very powerful, but what fun is that?

    Good eye on the websites!


  3. 953,

    I haven’t tested the 953, but I askede Joe Murfin, Daisy’s VP of marketing. He says the 953 is very accurate, but it doesn’t have a Lothar Walther barrel like the 853, so it cannot be considered as accurate as the 853. The 853 will shoot a 0.20 group of five shots at 10 meters – or a little better. I would expect the 953 to shoot a 0.25-inch group at the same distance.

    Until I test the gun, that’s the best I can do. Perhaps some 953 owners can enlighten us further?


  4. BB,

    Today I got my order from pyramid air.I got my eu jin .177 pellets and the beeman silver arrows.I want to review them in my 2 hours of testing.First,the silver arrow.It is quite accurate on my gamo cf-x but compared to the beeman kodiak,the kodiak is better.It hits pretty hard and I think ill be using it for middle range hunting.Now,the eu jin.WHOOOO!!!!!!!!!!!!!.Can you say


    The are very heavy pellets and are very hard to get into the cf-x breech.When I shot it It went pretty fast.I dont have a chrony but I would say 700fps.They seem to be accurate at short distances.Scince I had never seen them they where a suprise because they are HUGE.They look almost exacly to the beeman silver arrow only that the tip is round.It hits very hard and I think that this is a hunting pellet.I will save them for when I go hunting.Also in the order,my friend wanted a shadow black hunter so I got it for him.Ill be testing these pellets with the shadow.I also bought a leapers 3-9×12 AO mil dot ill ret R/G and some kodiak match for him.Ill be telling how I like the shadow compared to my cf-x shortly.Well if you think I left something out please tell me.Sorry for making it long.

    CF-X guy

  5. BB,

    Your right.But so many things so little money.I play electric guitar and thats another thing that I spend a lot of money into.I have spend over $3000 on guitars and amps.Also,I want the walther cp88 and im saving for it.Then I want the charlie da tuna trigger for my cf-x that will be 1.5lbs.And then I can try to buy a chrony.I know my ratings are sometimes wrong,but I know youll be there to correct what im saying.Still I have to buy the chrony.Im not going to buy it now but still,wich is the cheapest chrony that you would recommend?

    CF-X guy

  6. can you tell me alittle about the DIANA RWS MODEL 45 i puchased this gun used with a bushnell 3x9x32 sportview on it for $90.00 which i thought was a very good price any info would be greatly appreciated.. thank you Kenny

  7. B.B.

    When you said 853 is capable of shooting .20, does that mean at standing position? What if the gun is clamped to a vice or something? Would it shoot the same hole? Thanks.

  8. BB,

    Nothing is sacred in this world! Someone is signing posts with false names(initials). It is very upsetting, especially when they use MY initials. I did not write the above post about the Legacy!


    This blog is an excellent source of info, and is written by a very knowledgeable airgun lover. It’s read by lots of other airgun lovers. Lets keep it fun for all involved.

    JDB (the real JDB)

    p.s. Thanks for the update on the chinese pellets

  9. Daisy guy, I think B.B. meant 0.20. By they way, B.B., my 753 can shoot .1 or better, 853 has the same barrel and power plant, so i would assume it can get the same result. Is that not correct?

  10. Back to CO2..
    I have been told that I need a filter to catch particulates from the bulk CO2 tank. I don't think that scale etc. will form in a full tank, but??
    If you have your own bulk tank refilled, have the pressure diaphram replaced during the recert. A friend of a friend (for what it is worth) claims that his 20lb tank safety diaphram ruptured while driving. Instantly the car was filled with CO2 fog. He was able to piull over and get the door open while holding his breath.
    His tank had not been recertified.

  11. Most quality CO2 guns do have a screen filter to catch the particulate you mention. It's nothing as small as a precharged gun would have — just a wire mesh screen.

    I have refilled my 20 pound tanks (I have five) many times. No reputable fill station will fill a tank that's out of hydro, so your friend could have been doing things on the shady side when he got his tank filled.

    But a tank can hold for 20 years and thus be holding when the certification has long since lapsed. There is nothing wrong with that.

    The burst disk bursts when a certain pressure is exceeded, so the temperature in the car must have gotten too hot. I had a friend whose paintball tank let go in his car in the summer, too.


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