The magic of the O-ring

by B.B. Pelletier

So much of today’s airgunning depends on O-rings, yet how much do any of us know about them? Today, I’d like to tell you more and cover a few basics.

Different materials for different jobs
When CO2 cartridges were first used in airguns in the late 1940s, the choice of materials they could be made from was very limited. Most early O-rings in guns were made of a material that was porous to CO2 under pressure. After being in a gun and charged for hours or even days, the O-rings were swollen with CO2 gas! They were several times their normal size, which made it all but impossible to open the gas chamber to install another cartridge after the old one ran out. You had to set the gun aside for hours, to allow the gas to slowly leave the O-ring. If you didn’t wait, you would tear the O-ring by unscrewing the cartridge chamber when the ring was still swollen.

The Schimel was notorious for having O-rings that swelled!

Besides the American-made Schimel, guns made in others countries had this problem until very recently, with, perhaps, China being the worst offender of all. Now that you know about this problem, never try to unscrew a powerlet chamber when the cap feels extra tight. You might just encounter a 1950s problem all over again.

Hardness is another factor
The Shore durometer test gives you the hardness of rubber and other substances. The test measures the O-ring’s resistence to indentation from a known force. The O-rings we use are measured by the Shore D scale, which is for harder materials. You hear the phrase, “90 durometer” kicked around a lot by airgunners these days. A 90 durometer reading is VERY hard, but not all airgun O-rings are that hard. In fact, a lot of them wouldn’t work right if they were that hard. There is also a less well-known Rockwell hardness test for synthetic materials, but the Shore durometer rating is the one we use most.

Here are some O-ring facts.

1. To perform correctly, a hard O-ring needs closer tolerances than a softer O-ring.

2. An O-ring usually needs lubrication to do its job – but not always.

3. When an O-ring seals something, it only needs to be finger-tight.

4. An O-ring can look fine yet hide a tear or a puncture and leak under pressure.

5. An O-ring can look ratty yet still seal perfectly.

6. The durometer rating of an O-ring can change over time.

The seats or channels they sit in help O-rings work!
If the seats are too wide or too deep, the O-ring will not seal the joint as intended. Also, the shape of the O-ring seat or channel is somewhat important. While there is a lot of room for slop with an O-ring (that is one of their endearing qualities), you can’t get away with murder. A perfectly square channel with no radius in the corners may present sharp edges to the O-ring under pressure. In other words, it can cut the O-ring, causing it to fail quickly!

Sizes are important, too
Not only do O-rings come in different diameters, they also come in different thicknesses, and that dimension is just as important as the diameter. O-rings are available in both metric and imperial measurements. Sometimes, you can cheat and use a metric ring for an imperial application, just like a 14mm wrench will work when a 9/16″ isn’t available.

Properly designed O-rings seldom wear out
As long as they’re lubricated correctly (if they require it), O-rings can last a very long time. In some applications where they abraid as they are used, such as the seals around caps that are constantly opened and closed, they may wear out sooner, but I’ve seen O-rings that have lasted 25 years and are still going strong. If the material was chosen wisely and the seat is correct, an O-ring can last and last.

The magic word is silicone
It’s hard to beat silicone as an O-ring lubricant, unless the equipment specifically warns against using it. An arigunner should sock away some pure (food-grade, which is so pure it can be used in food machinery) silicone grease and a bottle of silicone oil. I have said this before, but nothing reseals leaking CO2 guns faster than a drop or two of Crosman Pellgunoil.

26 thoughts on “The magic of the O-ring”

  1. Interesting BB. speaking of rubber…

    I have a question… a little off topic.

    Do you have experience w/ rubber vibration dampners that affix to the barrel tip of rifels? Supposedly they act as stabelizers similar to archery limb vibration dampers. If you have, do you think they may help higher power airguns…like a tallon maybee?


  2. Turtle,

    I have tested some vibration dampers and they do wok on spring guns. I have never tested them on PCPs, but I know that muzzle brakes change the point of impact, so they do affect the vibration nodes.

    The only tuneable vibration damper I know of today is the Browning Boss. I suppose a cusom one could be built, and Dennis Quackenbush might be the person to build it http://www.quackenbushairguns.com.

    Good luck,


  3. Hey BBP, still haven’t gotten to adjusting the power and rechecking the accuracy on the talon…sure hope it will pull thru and I can shoot 100 yds again. I’ll be sure to let you know if its worth trying the kodiak matches in it. either way Im sure digital scale and a chronie are in the works. thanks for the detailed suggestions on both…

    so… here’s another completely off topic question. the recent pic’s of old guns leads me to the closet to brush one off n’ ask about mine. It’s a old 22 spring pistol called a “Hy Score Target model” y hy-score of Ny NY…only other markings..patent pending made in USA. the most unique feaure is the loading port on the rear that opens like an aperture by twitsing the rear. and the tapered bottle necked style barrlel. know anything of them?

  4. Turtle,

    This is to all the Hy Score pistol comments.

    The Hy Score pistol was made from 1947 to 1970. The design is a concentric spring/piston. in which the mainspring, the piston and barrel occupy the same space in the compression chamber. The barrel serves as the spring guide. This way the powerplant could be very compact, yet the barrel could be long. The Blue Book of Airguns tells a lot about the company and the various models of the gun. some of which are valuable.

    The pistol was made here in America, while Hy Score imported many different types of air rifles under their name.

    You have a unique collectable. I’d hang on to it.


  5. Thanks again I’ll have to see if I can find that book, it seems you refer to it alot. I also ordered an alpha crono and am planning on welding up a plate with a hole to shoot thru that will protect it downrange…Ill send you some specs on longer downrange shots and the beeman crow mags w/ the 12″ and 18″ barrel for your readers when things come together.

    I also reviewed the Pyramid article on the talon…Ahhh…I can see that tuning the tank to the most common power range(v.high for those long shots) will probably be necessary tobring things back to normal…what a relief.

    Im not certain of your affiliation w/ Pyramid but FYI I found a Limbsaver brand barrel stabelizer for $20 @ CheaperThanDirt.com, hope I’m not pushing the competition if you work for them. Thanks again for all the help.

    so many pellets, so little time.


  6. I heard that if you leave a co2 cartridge in the gun for like 24hours the cartridge will leak. I was woundering if thisis true and if so is there a way to stop this?

  7. I have a Walther Lever Action that has had two CO2 powerlets in it for the past 8 months. It still holds fine.

    Some inexpensive guns may have problems because of how they are constructed, but robust gas guns don’t leak.


  8. i have heard that even if your o ring is in good condition and you leave a co2 cartridge in the gun for like a day or so the cartridge will still leak. I was woundering if this is true and if so is there a way to stop this?
    Thank you-

  9. To B.B.
    I also have a HY-SCORE TARGET AIR PISTOL. In original box. On the barrel behind New York it looks like NY, but the N has no angled center line. Was this a stamping error or what? According to paperwork in box they also made a rear loading 6-shooter.
    Very impressive strength for a single cock air pistol

  10. I just found a HY-SCORE TARGET MODEL in my closet. The stamping is perfectly legible and there are some numbers below the stamping. 801189, model number, and I am really having a hard time trying to figure out how to use it. Any suggestions?


  11. Deej,

    Okay, your pistol was made in America.

    There is a latch that releases the upper part of the pistol. It should pop up a little when this latch is pressed. Try the right side of the frame, though I think it’s on both sides.

    Next, read this posting:


    The pistol is cocked by swinging the upper part of the gun forward until it cocks. Then swing it closed. Twist the rear knurled knob and a shutter will swing open. The pellet is dropped into the hole nose-first, then the shutter is closed all the way. The gun is now ready to shoot.

    Try this and see if it works.


  12. I’ve done all this, and it just dry fires. The shutter that you were talking about seems to open and close as it pleases, it doesnt stay shut. The gun may be broken?

  13. I see that you know alot about o rings and about air soft guns… i have a daisy powerline 15xt .177 caliber and i was wondering what kind of "o" ring do i need for this specific gun.. i currently dont have any idea of what to use, and i need help. any one can email me at s0ldi3r_0f_g0d_1@yahoo.com.

  14. I know this is an old thread, but I was wondering if any of you would know where I could get a replacement o-ring for the ring in the cap of the Co2 cylinder in an old Crosman 600 (circa 1960), the one in it has sat for 20 years and is completely ruined.

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