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Air Guns A proven CO2 fix for leaking guns

A proven CO2 fix for leaking guns

by Tom Gaylord
Writing as B.B. Pelletier

transmission sealer
Automatic transmission sealant works to stop slow gas leaks in CO2 guns.

This report covers:

  • Bad vibes
  • Unintentional test
  • Is the airgun I fixed still holding gas?
  • The test
  • More that just my guns
  • When does it work?
  • How about pneumatics?

This is a fun little report that I just happened to do, partly by accident. On August 28, 2013 I published a report titled Neat fix for bulk-fill CO2 guns. In that report I mentioned that Dennis Quackenbush had told me about a way to fix some slow-leaking CO2 pistols, using automatic transmission sealant. He puts it into the gas port on the gun, then blows it in when the gun is charged with gas. I reported trying it on a bulk-fill gun of my own and it worked.

Bad vibes

Immediately the comments started about how this sealant works by swelling the seals or turning them into a soft mushy mess, and that eventually the seals will fail if you use it. In a comment, I actually reported about 6 months later that the gun I had resealed this way was still working and holding gas, but that only started the warnings all over again.

Unintentional test

It has been nearly 2 years 5 months since I wrote that report, and last week a reader asked me about fixing a slow leak in a CO2 guns so I told him about it. When he responded that he was going to be cautious because he didn’t know what the ATF sealant might do to the seals, I thought it was time for this report! I told him I had been soaking the o-rings in sealant for 4 years, but it turns of that was not correct. It was 2 years 5 months.

My plan was to soak some common o-rings in the sealant for about 4 months and see what happened. I put some sealant fluid in a jar and dropped in a couple o-rings. And then I left them! I never got around to writing that report until now — 2 years and 5 months later. The o-rings have been soaking in the sealant continuously since I put them in!

o-rings in ATF sealant
Two common Buna o-rings have been immersed in automatic transmission fluid sealant for 2 years five months without any swelling.

flexible o-ring
The o-rings are not soft or brittle. They still have the same flexibility as when they went into the fluid.

Is the airgun I fixed still holding gas?

I would love to be able to tell you that the Crosman 116 .22-caliber bulk-fill pistol I fixed this way was still holding gas. But it isn’t. I tried it when I began writing this report. It held gas for months but not for years.

I also took a leaking Crosman 150 and added some ATF sealant when I started writing this report. This is a pistol that uses a 12-gram cartridge. The fluid sealed the gun immediately and it was still shooting and holding 24 hours later. I cannot hear a leak of any kind.

More that just my guns

I’d like to point out that over the years this test has been running I have advised several blog readers with leaking gas guns to try this. Some have and I have received several reports of it working fine. I have also fixed several other of my own cartridge gas guns (12-gram) this way. So I’m not just telling you the sealant doesn’t hurt the seals — I’m also telling you this really works to seal leaking gas guns — regardless of whether they use cartridges or are bulk-filled.

When does it work?

This doesn’t work on guns that have fast leaks. If you can hear the gas leaking out when you charge the pistol, this isn’t going to work. It works on guns that take 24 hours or more to leak down.

It works immediately upon application. Since the seals do not have to soften or swell for it to work, it takes no time at all to seal the leak. If the leak isn’t sealed right away, it’s probably never going to work.

This stuff works better than Crosman Pellgunoil for stopping slow leaks. I would still advise using Pellgunoil in the beginning for as long as you can, though, as it contains an o-ring conditioner that I’m not sure the transmission stop leak has. Use Pellgunoil first and when it doesn’t work, use this stuff.

How about pneumatics?

I have tried this stuff on multi-pump pneumatics without success. My testing wasn’t very scientific, I just tried it in a couple old leakers, but there is nothing to report.

That’s it for this report. I just thought I’d put an end to the conversation about what this stuff does to airgun seals. I doesn’t do anything except stop slow leaks.

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.

51 thoughts on “A proven CO2 fix for leaking guns”

    • B.B. after reading your original post I was back home in a half hour trying it out.I take and draw it up in a syringe squirt it in,works great. got several pump guns shooting too 880 881 daisys, 140 114 crosmans 312 ben. . But alas no go on my apache. anyhoo thanks for the tip.

      • Yesterday the spare mag for my KWC Makarov PM (4.5mm blowback) developed “instant discharge” disease. Wasted 3 co2’s but got it down to a slower loss. Saught help on the WWW and came upon this Bar’s Leaks suggestion. Found a supplier on e-bay here in the UK & received it this morning. Found a syringe, which came with a printer cartridge refill kit and filled the valve and treated the white capsule seal. Left it just a couple of minutes and, hey presto, instant cure. As it’s my old original mag I’m quite happy to monitor for any seal rot problems. Many thanks for the advice.

  1. B.B.,

    I believed you when you first reported this. After all, Tom Gaylord and Dennis Q., right?

    However, if you think just because you have proven that this technique does not turn seals to mush, I have some swamp land in Florida to sell you. To a lot of folks convincing proof isn’t convincing enough. You will catch heck on the boards for this post regardless of your proof.

    As for me, I had forgotten about this cool trick and have a few leakers to seal up this week!


  2. I’m serious here not trying to imply anything.

    So exactly what does it do to the o-ring to help it seal in the air gun?

    When you take the o-ring out of the stop leak does it feel sticky on your fingers?

    Maybe it helps the o-ring kind of glue itself to the surface its trying to seal. ???

      • BB
        That’s right on the moving part. So pretty much it helps on a air gun that has a flat seal leaking. Like the one that the head of the Co2 cartridge butts up against.

        I wonder if you took those o-rings and set them on a flat piece of a clean steel plate and let them set overnight if it would then become sticky to the touch.

        If the o-ring is submerged in the liquid stop leak there is no way for air to hit it like in a air gun and for sure right when you take it out and its dripping wet. And I don’t mean a blast of air pressure. Just the air around you.

        Maybe the stop leak creates a film on the seal and metal surface. Don’t know. Just a thought.

  3. BB– re when does it work?–almost 2 years ago I bought a like new 1077 that was made in 1994. It was in the original box and had not been shot for many years. ( according to the seller). It leaked the entire co2 cartridge, in a few seconds, as soon as it was pierced. 4 pellgun oiled cartridges later, it no longer leaked and it is still working without a leak. It would seem that the seal was not ruptured of cracked, only too hard to work. The pellgun oil must have softened it so that it formed a seal. This technique did not work on several of my pistols, but they had seals that let the co2 out instantly. Pellgun oil might work on some guns that have fast leaks , as it did for my 1077. Ed

  4. Interesting…

    PCPs have a number static O-rings that might benefit from a tiny bit of the automatic transmission sealant being brushed them on before assembly so the parts are not going together dry.

    Wonder if some “divers silicone grease” – just enough to put a shine on the O-ring – would be a good idea for dynamic O-rings. Not for the high-pressure internals on a PCP which are extremely sensitive to contaminates but on pellet-probe O-rings and such.

    Any thoughts on this?


  5. The stop leak collects in crevices and basically coagulates under pressure. It is also made to condition the rubber gaskets throughout the transmission so I cannot even begin to understand people assuming it will dissolve rubber o-rings, its essentially a thick oil with LIQIUD RUBBER polymers mixed together. Sounds like a perfect, huh, stop leak?, to me. Lol. People are silly.

    • RDNA
      We have a type of AW46 hydraulic oil at work that has some additives mixed in. Of course our supplier won’t tell us what it has added to it. It’s a little thicker viscocity than normal AW46 hydraulic fluid without the additives.

      The stop leak BB shows above looks alot like the color of the hydraulic fluid with the additive at work. I wonder if that is all the stop leak is.

      And what I was asking about above if it is sticky when it drys and has a film on it kind of goes along with what your saying about the coagulating under pressure.

      With a Co2 valve that is in a air gun there are two basic leaking points on that valve that would cause the pressurized Co2 to leak out of the gun. The flat seal where the co2 cartridge bumps up against and pierces the cartridge. Then there is the seal that releases air to the transfer port orifice when the hammer striker hits the valve stem.

      Both of those seals are exsposed to atmospheric room pressure or air at some point in time. I can see the stop leak coagulating around the seal that releases air to the transfer port orifice and the air hitting the stop leak and sealing it by possibly getting sticky or thick. And that particular seal is usually the one that causes a slow leak out of the barrel of the gun. PCP guns will do that if the striker is resting on the valve stem and very slightly letting air leak by.

      Remember the stop leak was invented for automatic and manual transmissions. And they do have a air vent hole at the top of the tranny’s. A manual and automatic transmission is not filled to the top with gear lube or trany fluid. There is open air areas in those tranny’s. So possibly as the tranny works it keeps mixing the fluid and stop leak and then after it splashes up in certain areas it drys or thickens a bit and helps form a seal around things.

      BB’s test of leaving them soak in it just proves they didn’t soften or maybe didn’t swell. I don’t see any measurments of the o-ring size before they were soaked or after. So it could of swelled the o-rings also. Which is no big deal. The main thing is they didn’t soften or deteriorate. So then the stop leak could be a good thing. Of course repairing with new seals would be the right thing to do.

    • RDNA
      I cannot speak to the formulation of the current day stop leak products on the market but to only say that technology has grown by leaps and bounds in terms of chemical compounds and oil advancements.

      I can however speak from 45 years experience as an ASE master certified technician for those 45 years that the stop leak fluids of the 70s, 80s and 90s did in fact destroy seals and o rings in engines and transmission due to softening and swelling of the seals. I know from first hand experience in rebuilding and resealing engines and trannies that had the stop leak fluids used in them and when inspecting and replacing the seals the were most certainly damaged more so than seals that had began failing but not had stop leak fluids added to the engine or trannies.

      It may be that heat and movement that the seals are subjected to in a motor vehicle cause the failure of the seals as compared to in an air gun that does not have movement or continuous heat applied to the seals but you and all others can make your own decisions.

      I know my self never have and never will use any such product in my vehicles and likely not an air gun either since if it is leaking it means there is a failed seal that requires replacement. I understand that requires more work than just a few drops of fluid but there is a saying in the auto industry of ” pay me now or pay me later” and later always cost more.

      Just my opinions and 45 years of experience on the front line of repairing ALL types of failures a motor vehicle of any type can and do have. So next time you have a small radiator leaks go ahead and put some Bars leak radiator stop leak in it and in 6 months when the radiator is plugged and the engine overheats and blows the head gasket requiring not only the radiator to be replaced but also major engine work if not replacement don’t say I did not warn you.

      Seen it far to many times to believe any different. seen a 250 dollar radiator replacement turn into a 5000 dollar engine replacement and the same scenario for auto trannies as well going from a simple seal replacement to a complete overhaul in a matter of months.

      Maybe the current fluids are better but you will still never see me use it as its nothing more than a bandaid on a wound that needs stitches.


      • I like the anology of it being a bandaid, exactly. It wont fix anything but but some cars and airguns arent worth fixing, just bandaiding till the wheels fall off. I dont know about the old stuff, but tranny fluid in general smells noxious, I can imagine the old stuff wasnt very ph balanced either. Well at least we can put to rest that the new stuff is none corrosive to rubber, and where the confusion comes from where people having experience with the old battery acid formulas would advise not to use it. Luckily things are always improving as far as car fluids go, though I think titanium liquid infused motor oil is probably the skys limit! Man how times change, it must have been the fluids that kept the old cares down in mileage before their early demises, gunfun and others werejust discussing that something like 100,000 miles was often very good.

        • RDNA
          Sorry for the late reply as I have not been feeling well.
          I agree its not a fix and some guns are either not worth spending money on or parts are hard to find so if it works then go for it. I am sure the current days fluid fixes are far superior to those of 30 plus years ago but having seen the effects of people using those stop leak and bandaid type products first hand as a mechanic that had to repair the engine and trannies that it was used in I cannot bring myself to use them or recommend their use to anyone.

          I have my doubts that Titanium infused oil is going to be any better in increasing engine life than good old fashioned preventative maintenance ie. ( changing oil in a engine every 3000 miles or every 15,000 in an auto tranny ) The cost of that fancy oil is only beneficial if left in for 7500 to 10.000 miles and the new ford escape I bought in July states that it can be driven 10,000 miles between oil changes by ford but mine will never go more than 3000 mile between changes so call me old skool or whatever but I stand hard and fast by pay me now or pay me later and the fluids used in todays cars are even more important than cars of the past since todays cars cooling systems are designed to be just capable of handling the heat these new cars create as compared older cars that had a cooling system designed at 2 to 3 times the required capacity to keep them cool.

          Todays cars are on the ragged edge of burning up all the time so as to reduce weight and cost to manufacture. It only takes a small loss of coolant in today cars to allow them to overheat and require high cost to repair whereas an older car had to loose over a gallon of coolant before it started to overheat and gave an observant driver ample time to prevent serious damage by filling the system back up to get it to a place to be repaired.


          • Not to worry, my sickness just broke waking up from an hours sleep just now. No sleep yesterday from shivering the fever trying to break and it tried creepung back on earlier before I fell asleep. Absolutely vicious gift from the kids school. Maybe just getting old, but even the kids were wrecked while the fevers glowed on, but a full 24 hours is about all that you’d notice of it bothering them. Sometimes I wonder if the common cold is ever gonna evolve, thinking about the constant “war on flu”. On the car durability, spot on, did anybody ever really get far with pantyhose as a belt? Lol, you could never dream of substitutes or mickey mouse riggin that was frequent and comically unique to each vehicle. Some were standard tricks, others just seat of the pants luck but either way, cars, new cars, are just not the same adventure they used to be.

  6. RifledDNA22

    That makes good sense – moves to the leak site with the flow and coagulates under pressure.

    …A Google on “O-ring lubricants” brought a ton of hits… now I have my lunch-time reading material 🙂

    • Vana2

      I started on a design for an electric motor and pulley system for my hand pump today. I wanted to use a small 1 inch pulley on the motor with one large pulley hooked to the pump. I did not realize that for the 4 seconds per stroke the large pulley would need to be 10 feet in diameter for a 1800 rpm motor. If my math is correct. I can use a two pulley system as some of the others have made and keep the pulleys at two or three feet. I was thinking one large wheel hooked to the pump would look cool in my workshop. Ten feet is a little much though. I think I will still have at least a 3 foot pulley hooked to the pump for visual effect. I won’t be moving the contraption around.

      I did some more thinking on the hydraulic ram idea and figure it may not be as complex as I thought originally; especially if the ram is controlled manually. As long as the ram stroke is longer than the pump stroke it could be mounted in an adjustable slot. The slot would allow the ram to match the stroke of the pump. A little safety factor would be wanted at each end of the pump stroke or goodbye pump.

      I do not remember the thermodynamic gas laws real well but I think that the heat generated is independent of the time in the compression stroke. That would mean that the overall heat generated is based on strokes to minute. So a slow stroke with no pause would be the same as a fast stroke with a pause at the top and bottom. With the crankshaft flywheel method the stroke would be slowest at each end of the stroke. That would help give the intake and exhaust air on the pump some time.

      Let me know if you give it a try. I am going to use as much scrap parts as I can. That is just the way I am.

      Good Luck

      • Don,

        Seems that we are similar in our thinking and our methods. I have several boxes of “good for something” odds and ends that get incorporated into various projects. Its amazing what you can make out of bed-frame angle iron and other scrap parts. 🙂

        Since I have an electric wood-splitter I will probably look at using shock absorbers as pistons. I expect that they are available in different bore diameters (trucks vs cars) so I have to do some research and then some calculations. Might be possible to use multiple absorbers in a parallel and/or series array to get a multilevel pump configuration. With 6-tons of force available I should be able to compress a good volume of air to a high pressure with relatively few strokes.

        The slot-in-the-ram is what I was thinking about as well. The stroke on the splitter is controlled by a hydraulic switch. Might be possible to hook up a actuator that could control the switch and the length of the stroke.

        Have fun with your pump automation and please keep me informed at to how it works out.

        If you like you can contact me directly at hankvanderaa at gmail dot com.


    • Reb
      I just searched them. That is what I’m talking about we have at work. Viton is the material that the ones we have are made out of. So I guess that’s why we call them viton seals. I don’t know just what we always called them.

      But as far as the o-ring mod on the 300 goes. We are useing a much smaller o-ring than the diameter of the groove in the piston. So we are stretching the o-ring pretty tight in the groove. It’s not relaxed in the groove like a normal sealing o-ring would fit the groove. The normal fit o-ring might have a slight snug feeling to the groove diameter. But that’s not how we are doing the 300 o-ring. We don’t want the o-ring moving or expanding or pulling in or any other stuff. And the outer diameter of the o-ring is very slightly contacting the cylinder wall. We want good sealing and slight drag. So a little different situation than how a o-ring works with HPA or hydraulics.

      • It took me a couple searches to find a catalog but I did and they’re touting lower drag and break-away tension with channels to store lubricant and lower tendency to roll or spiral in it’s channel.

  7. When B.B. ran the first report on this I couldn’t wait to try it. I had three Daisy 200 semi auto bb pistols (C02). They would just leak badly when the C02 cart was installed. They leaked somewhere in the gun itself, not at the cart. I took one a part to see if I could fix it. Never could. In fact I trashed the gun trying (yes I tried on the one that was in the worse looking shape and had no box for it). I tried endless carts. with Crosman pelgun oil on them. I looked all over the internet trying to find someone to repair them. No one would that I contacted. Then I tried the trans stop leak after reading B.B.’s report some time back. On one gun it work and on one it didn’t. The one it worked on is still doing well to this day! Thank You B.B.!

  8. On a different note, I put in the holidays reading about the Battle of Waterloo. The big message I got is that the British redcoats who were the villains of the American Revolution were the total heroes of this battle. They were against tyranny represented by Napoleon’s despotism which went way beyond their constitutional monarchy, and the redcoats really were the finest troops in the world. The climactic moment came when they were arranged in infantry squares and held off both the French cavalry swirling around them and the French artillery blasting away at them. Astounding. How the heck did we win against them?

    The Minutemen obviously played a role, but shooting from behind trees and stone walls was not a war winning strategy. One of the keys apparently was developing American line infantry, starting at Valley Forge, who could actually stand up to the redcoats in battle which was quite an achievement.

    Anyway, the key to the British success seemed to be a discipline that allowed them to maneuver in battle and sustain more rapid fire with the technology of their times. The Napoleonic wars are long done, but I understand that rapid, massed rifle fire remained a doctrine in the British army right up to WWI and was engineered into the fast firing Lee-Enfield bolt design which set some astounding speed records at the time. So, history lives, and it makes me want to take out my Lee-Enfield No. 4 Mk. I.


  9. Still haven’t had any luck saving a pump gun yet but the only negative so far is that pellgun oil is much more fragrant.
    I couldn’t find my pellgun oil when it was time to try my 2400kt so I used a drop of this instead and it took a couple months to get the smell out, no problems at 2250psi other than the smell every shot.

  10. hello i have a winchester walter, cal 4.5 pellete, with scuga of 85gr. When i put the co2 this leave the rifle and the c02 scuga dont work anymore. how i can solve this problem?

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