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Ammo Giffard Carbonic Gas CO2 rifle: Part Three

Giffard Carbonic Gas CO2 rifle: Part Three

Giffard carbonic gas (CO2) rifle.

A history of airguns

Part 1
Part 2

This report covers:

  • Cloud Nine to the rescue
  • Leaks
  • Fix the Giffard valve
  • Over to BB
  • Ammo
  • Velocity 1
  • Tank off
  • Velocity 2
  • Summary

Today we begin looking at the operation and performance of the Giffard Carbonic Gas CO2 rifle. As may recall, in Part Two I reported that there was no adaptor to fill the Giffard’s removable gas tank, so there was no way for me to fill it. Fortunately this blog has the services of reader Cloud9.

Cloud Nine to the rescue

I contacted him and asked if he could help me. He graciously consented. Fortunately he had acquired a metal lathe a couple years ago and knew how to use it. That was ideal for what had to be done. So I passed the rifle to him.

I showed a You Tube video in Part 2 that was so informative that I want you to watch it again. It shows how this rifle works.

Cloud Nine made an adaptor to fill the Giffard’s tank.

Giffard make adaptor
Cloud9 made an adaptor to connect the Giffard tank to a bulk CO2 tank.


When the Giffard tank was connected to the bulk CO2 tank he discovered that the valve in the  Giffard’s tank leaks. That valve is both an inlet valve and an exhaust valve. It’s the only way for gas to get into or out of the tank.

Giffard tank leaks
When he was able to connect the Giffard tank to the bulk CO2 tank reader Cloud9 discovered that the Giffard tank leaked.

Fix the Giffard valve

To repair the Giffard valve Cloud9 had to disassemble the tank and remove the valve parts. It was a straightforward process because the valve is simple, but getting it out of the Giffard wasn’t easy.

Giffard valve
Cloud9 had to disassemble the Giffard tank valve to repair it.

He told me the valve had been repaired or modified since the gun was made. The valve seat that would probably have been made of animal horn is now a very hard synthetic material.

The tank had rust inside that he tried to remove. He got most of it but said if any that remains flakes off and gets onto the valve it will probably start leaking again. When he returned it he said it had held gas overnight.

Over to BB

I got the rifle back a week ago and last Friday I did the test that I’m about to share. First I took the rifle out to my garage and tried dry-firing it. No gas! It had leaked down in the time I had it.

I filled the tank at room temperature, which isn’t the best practice, but I was so excited to test the rifle!

Stock Up on Shooting Gear


Giffards were made in at least three calibers — 8mm and 6mm are common and 4.5mm (.177 caliber) is rare. My rifle is 8 mm which is the most common. I have Hornady .32-caliber swaged lead balls that measure 0.310-inches nominally. Since 8mm is close to 0.315-inches, nominally, they should fit. I found that some dropped into the loading tap while others were slightly too big to enter. That doesn’t means the balls are as large as 8mm though. It could also mean they are slightly out of round.

Giffard ammo
Hornady .32 caliber lead balls seem almost perfect for the Giffard.

Giffard tap
Some .32-caliber balls drop into the loading tap, while others like this one, stick in the top. It may just be out of round.

Velocity 1

Remember that I filled the CO2 tank at room temperature. Because the pressure of CO2 is temperature dependent, the fill went very quickly. I got three shots from the fill. They were:

Shot………..Vel. f.p.s.

It was obvious the tank was running out of gas, so I stopped shooting.

Tank off

I took the rifle into my kitchen and removed the tank.

Giffard tank off
I removed the Giffard tank…

Giffard tank refer
… and put it into the refrigerator to cool.

Cooling a bulk-fill CO2 tank is an old trick to get more gas inside. If the tank is warm when the liquid CO2 flows in it flashes to gas, raising the pressure and preventing more gas from entering. If the tank is cool more liquid flows in, resulting in more gas.

Velocity 2

After 2 hours in the refrigerator I removed the tank. I wore gloves this time to keep from warming the tank with my hands. Then I immediately filled the tank again. Here are the results from that fill.

Shot………..Vel. f.p.s.

I stopped there. If the tank was colder would more liquid CO2 flow in? Certainly. But this Giffard tank is over 140 years old and it doesn’t need to be stressed that way.

The .310 round lead balls weigh 45.4 to 45.8 grains. Using 45.5 grains as a data point I calculated the muzzle energy of the rifle at its highest velocity. It’s surprisingly low, at 29.47 foot pounds.

I may shoot the rifle for accuracy, though these undersized lead balls probably won’t help  things. I WILL NOT mount a scope or dot sight, and if anyone suggests that I will come to their house at night and let the air out of their tires! That’s like suggesting that the ceiling of the Sistine Chapel could use a second coat!


Thanks to the efforts of reader Cloud9 my Giffard is now working. It is a curious non-powder-burning arm that I group with airguns, though it doesn’t actually use air. Curiously, it is the very first gun to use CO2, yet its design is extremely advanced.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

20 thoughts on “Giffard Carbonic Gas CO2 rifle: Part Three”

  1. BB,
    That’s four fairly powerful shots…pretty cool! 🙂
    I’d be curious to see an open-sight accuracy test; she should make a nice plinker.
    I think it’s awesome to see this old gal restored to shooting capability (good job, Cloud9 =>).
    That’s one sweet piece of history you’ve got there.
    Blessings to you,

  2. BB

    Any more close up views of the valve?

    Hope you will shoot her at around 50 feet to get some idea of accuracy. No, we don’t need the Meopta mounted.


  3. BB,

    If Cloud9 can make a replacement valve for the Giffard maybe he or some other person with the necessary skill set can make an adaptor to allow use of a 12 gram CO2 cartridge so that you don’t have to strain the old tank and have a (possibly) easier time in shooting it. It’s going to take a while to achieve 5 shot groups let alone a 10 shot group.


  4. Tom,

    Antique air guns like Giffards remind me that great designs and pretty impressive technology existed long before we often think it did. (And I love the steampunk look, very Jules Verne-like.) A hair under 30 foot-pounds seems low, yes, until one tries to list CO2 air rifles that exceed that number. A Palmer Cap’Chur long gun shooting a 185 grain slug or a Farco long gun might get into that range, but I have difficulty thinking of others.

    A very good report.


  5. B.B.,

    Although the threads are very fine on the tank is that the leak point? There is seemingly no place for gasket or o-ring.
    You probably know all this but…are you certain you are getting liquid CO2 out of your bulk cylinder; i.e., have a siphon/dip tube correctly installed? IF not, you can invert the bulk fill cylinder to get the CO2 gas away from the shutoff valve until a proper tube is installed.


  6. Michael,

    Any number of CO2 Big Bores and even .25 caliber guns from the Philippines will far exceed the Giffard’s power level. I have an Airrow Stealth that will exceed that by at least 30 FPS in .25 caliber and a 9mm that will get even more.
    It is super dependent on ambient air temperatures and how quickly the liquid/gas in the gun’s cylinder, plenum, valve, and the barrel reach ambient temperature as well.


  7. B.B. and Readership,

    A little more about RUST!

    The first item is mostly for Tom and his Giffard cylinder:
    “In the presence of water, carbon dioxide reacts to form carbonic acid. This electrolyte can speed up the rusting process and cause corrosion.
    Therefore, even if you don’t live in a humid climate, your metal surfaces may still rust if they’re exposed to carbon dioxide and water.”
    Note well (n.b.) that Carbon Dioxide (CO2) and water (H20) join to form Carbonic Acid (H2CO3) so in doing that it frees an Oxygen molecule to do the EVIL rusting!

    KEEP THE BOTTLE DRY on the inside.
    Do not open the valve unless it is connected to the fill cylinder or the gun. Briefly Burp the Shut Off valve on the bulk cylinder just prior to filling in a well air conditioned and/or dehumidified space; not the garage or out of doors when not in a very dry desert!
    A dive shop or hydro testing shop can remove the corrosion in that Giffard Cylinder better than anyone else; if you want to keep the original Giffard Cylinder.
    I would have an adapter and valve made to fit a modern CO2 bottle if you intend to shoot this great looking gun much in the future.

    For the General Readership:
    These folks know what they are talking about…unlike most all the blogs about PCP pressure vessel and corrosion.


    PS: i hope this kind of action against Criminals and Delinquents catches on around the World: https://amp.cnn.com/cnn/2023/06/09/asia/sushi-chain-sues-boy-licked-soy-sauce-bottle-intl-hnk/index.html Lest you think it too severe for the bottle lick he also licked his fingers and ran them over the Sushi (other people’s) on the belt and a cup which he returned to the dispensing tray! It wasn’t the Sushi or the Restaurant that made him do it. People choose to do bad THINGS, NOT things!

    • How is it that a thin layer of oil can “keep oxygen and moisture from reaching the metal”? That never sounded convincing to me, as oxygen and water can diffuse into say, cells, effectively though several layers of oil (cell membranes). I propose the oil or wax or whatever is doing something else: perhaps it is a low-temperature “flux”, a reducing agent that gets oxidized instead of the metal.

      The punishment for licking the a sauce bottle should be to chug the bottle of chili oil next to it!


    • Dave,
      I think that were it my own I would be reluctant to use HPA above the normal vapor pressure of CO2. Even if regulated, my fear of “Murphy’s Law” wouldn’t allow me to let any higher pressures anywhere near it.

      I would think that a pretty realistic replica of the tank could be made that would allow two or three 12 gm cartridges to be inserted, allowing for a great many shots before refilling. Add to that the drop of oil placed on the tip of each cartridge and I believe the rusting issue would be relatively moot.

      Just a stray thought from the peanut gallery.

      • There are tanks made regulated to within the power levels of CO2. That is what I was referring to. I agree with you about not wanting to overpower the gun.

        • I don’t doubt that at all, Dave. It is just my own innate fear that “if something CAN happen,, it eventually WILL happen”.
          And no,, I don’t think I have any ancestors named Murphy,, just a lot of experience with things going amiss.

  8. Tom I am so glad you got the old girl up and running. The fill adapter I included with it was made by Dennis Quackenbush. I do remember attempting a fill from a 20 lb cylinder
    But the pressure vessel leaked it out.
    That was as far as I got…… Even as a plumber I was scared to death to try to open the gas cylinder.
    Such a wonderful old air gun. I must also confess I’m the one that shimmed the rear sight. Thank you my health has kept me from thinking about air guns for 6 months and this is very therapeutic.
    Frank B

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