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CO2 Neat fix for bulk-fill CO2 guns

Neat fix for bulk-fill CO2 guns

by Tom Gaylord, a.k.a. B.B. Pelletier

Today, I’m going to tell you about a low-cost fix I got from airgun maker Dennis Quackenbush for bulk-fill CO2 guns.

Dennis bought a Crosman model 116 bulk-fill pistol that leaked, and rather than changing the seals, he injected automatic transmission sealing oil into the gun and sealed it that way. What this sealer does is rejuvenate the synthetic seals and make them swell to do their job again. Dennis said the procedure worked well in his gun.

Could I do the same? In the past, I have written about “fixing” CO2 guns by injecting several drops of Crosman Pellgunoil into the gun with the charge of CO2. That works for both bulk-fill guns and for those that use cartridges. This would be the next step. I just happened to have a Crosman model 116 bulk-fill pistol on hand that hasn’t worked in the 5 years I have owned it. I think I paid $30 for it at an airgun show, and did so hoping to fix it with Pellgunoil. I tried, but the seals were too far gone, and it didn’t work. So, I set the gun aside, always intending to do something about it.

When Dennis told me his trick, it was like getting an entire carton of round tuits! I went to the local automotive store and picked up a plastic bottle of automatic transmission sealer. I purposely did not ask Dennis to tell me the brand of sealer he used; because if this trick is going to work, it should work with any sealer on the market. So, for $5.50 plus tax, I bought what is probably a lifetime supply of bulk-fill CO2 sealer.

transmission sealer
I picked up a bottle of automatic transmission sealer at an auto supply store.

How does it work?
To get the sealing oil into the gun, you put it in with a charge of CO2 gas. On a bulk-fill gun you remove a brass screw at the end of the reservoir that opens the port for filling. Drop the transmission sealer oil into the opening with an eye dropper. Then attach the bulk CO2 tank and open the gas flow. The first few times I did this, nothing happened. The gun continued to leak gas. But some of the sealer was blown into the gun each time I tried to fill it. Then, on the third try, the gun finally held some gas. I could actually hear the inner seals as they swelled and the gas stopped leaking. That fill only put in enough gas for about 6 weak shots; but it set things up for the next fill, which I believe was complete.

Crosman 116 pistol
Crosman’s 116 bulk-fill pistol is a .22-caliber single-shot pistol with power and accuracy that surpasses many of today’s air pistols.

After the next fill, I had shots at the power I expected from this pistol. Since I’ll test it for you in a 3-part blog that’s coming up, I’m not going to report the power today, nor the shot count, but I expect to get 25-30 powerful shots per fill from this gun. That’s what similar models gave in the past.

Crosman 116 pistol fill port
The pistol’s fill port is covered by a brass screw on the muzzle end of the gun. Remove the screw and attach the bulk-fill tank to this port, snug it against the rubber seal at the bottom of the port and open the tank to let the gas flow. The fill takes about 2 seconds. This port is where several drops of transmission sealer oil are placed before the tank is connected.

Now that the pistol is holding gas again, I plan to test it for you completely. That’ll be a treat because these old gas guns are both powerful and accurate, as well as having advanced features such as adjustable sights and power.

My thanks to Dennis Quackenbush for passing along this tip. It won’t always work, of course, but it’s just one more maintenance trick for your bag!

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.

57 thoughts on “Neat fix for bulk-fill CO2 guns”

  1. Very neat trick BB.It seems it should have a chance of working on lots of the older guns that had pressurized powerlet chambers too….like Crosman 150s or Benjamin 422s.I’ll try it out and report in my results.

    • Frank,

      Why just pressurized chamber CO2s? Might this work in conventionally charged powerlet guns?

      If so, this would be a revelation for the reseal-challenged, such as yours truly.


      • Hi Michael…..I would imagine the real challenge would be delivering a signifigant amount.Maybe try using a plastic or metal tube with a few drops in it (keep a finger on the end to create a vaccum like a soda straw until it is in place) Then I would blow it in there carefully while dry firing it if possible,otherwise the pressure will just push it back out.Then try a powerlet,and repeat as necessary.

  2. Good tip, BB. Btw, a 50/50 mix of automatic transmission fluid and acetone makes a superior penetrating oil. It should work just as well with the sealing type ATF.

    • I’d want to read the ingredient list before trying on a PCP.

      ANY petroleum based compounds could ignite under the pressure of a PCP (though not as badly as pure Oxygen — cf “A Whiff of Death”, Isaac Asimov).

  3. OK – $64 question – should a CO2 powerlet or even a bulk fill gun hold it’s charge for an indefinite period of time much like a pneumatic pump up rifle such as the 392? Anyone have any experience as to how long the CO2 charge will last in a stored gun?

    Fred DPRoNJ

      • What BB said…..I have a Crosman 111 & 112 that have held for around 10 years that I know of.In fact they show none of the telltale signs of ever being dismantled,and small brass screws are real prone to show evidence of tampering IMHO.

  4. BB said..”It should work on single-stroke and multi-pump pneumatics.” My 392 will not hold air, where would I put this trany stop-leak to see if it will help? Thanks

    • Gene,

      Put it where you are putting Pellgunoil now. And if you haven’t been doing that, start with Pellgunoil and not this.

      It goes on the end cup (the pump cup_ that compresses the air and forces it into the reservoir, so flip the rifle on its back, open the cocking arm and look at the end of the pump slot.


        • It worked !! I got the same kind of ATF stop leak BB did, just by chance. My 392 would not hold air so I tried the ATF stop leak. I put some in as BB suggested. I shot it a few times and it did not help any. Before I did this it would hold air for several seconds before it all leaked out. I added some more stop leak and pumped it up one time and let it stand on the rifle butt for a couple days. Shot it and It did hold at one pump but at pump 3 I could hear it leaking. I shot it a few times and it was still leaking. I let it set for some 3 weeks on the butt plate, I kinda forgot about it. Yesterday I got it out and pumped it 2 times, no leaking sound. Shot a few pellets and it was working fine. I then gave it 3 pumps and it held air and shot well, at 10Ms. I shot it several times and all was well. Was afraid to pump more than 3 times, afraid it would start leaking again. ?? What may have helped in my case is that I did not pump it up too much, slowly increasing the pumps over time. Since this is the only time I have done this fix, that is just a guess. Thank you soooo much BB, an early (almost free) Christmas gift to myself.


  5. I’ve seen transmissions with piston seals that expanded until they looked ridiculous and were sheared off by the pistons. This was due to something being added to the oil. Also seen master cylinders topped off at a quick lube with wrong stuff in them that caused the lid rubber seal to pop out when lid removed at 4 times it’s original size, resulting in locked up brakes from pistons seizing, all rubber items needed changed.
    But in the transmissions, I have no idea how much sealer the person used, or what type, It was always folklore that people would put strange stuff like brake fluid and oil in to soften seals. If you have a junk transmission and jugs of stuff laying around, it is considered a no loss if you kill an already dead transmission I guess.
    I’m just thinking this wouldn’t be a good regular use item for a working non leaking gun, but one with problems, why not.

  6. This is a trick I never thought of. Would it work on a Discovery? I have one that has leaked ever since it was new. I’ve sealed it several times and it always has a leak someplace I cannot seem to fix. I’ve cleaned and polished everything inside until it glowed with a military shine, cleaned everything to a surgical suite level of cleanliness, and even tried to make the o-rings a hair bigger with teflon pipe tape. Nothing has ever worked. I put my ear to it and I still hear the tiny wet bubbly leaking sound. I’m getting a bot desperate to find a fix.

    • John,

      No. Don’t use this in a PCP. I don’t know how this oil reacts to pressure. I do know that a multi-pump stops at around 1,500 psi, but your Disco goes up to 2,000 psi. I wouldn’t recommend it.

      It sounds to me like you have a pinhole in either the metal parts (not that common, but it does happen) or in one of the seals. It looks good when thee’s no pressure, but under pressure the hole opens and air passes.


      • In that case my next move is to begin replacing major pieces of this gun. I kind of have to now since the last time I tried to seal the gun the air pressure gauge shot out of the gun and flew across the room destroying the gauge (Only had 2000 psi in it) Turns out the part the gauge screws into finally gave out after so many attempts to repair it. I’ll just set this project aside for a while since I have a much bigger build in the works right now. I’m working on putting a piston actuated ar-15 together. (No more gas tube to foul the gun up.)

        • John,I would go over the gun with water w/ soap to find the actual site of the leak……then a dab of JB weld or even silicone caulk from the inside may save you some money.The AR 15 project sounds like fun!

          • I’m way ahead of you on this one. I already thought about it. I even went over the gun with soap. Seemed my soap was a bit on the corrosive side since I ended up going in to clean off some nasty rot on my next try. I’ve tries everything I can think of. And since I now have a stripped out air gauge I’ll just sink the money into a whole new air valve and other suspect parts. Then I’ll try to come up with a way to set some silicone sealant in the thing and hope for the best.

            Yeah, the AR build is going to be very interesting. The lower is not aluminum. It’s an all new polymer product that is supposed to be stronger than the aluminum of a normal lower. I figure since I’m going all high tech I might as well go all the way with all the latest tech out there. A standard gas operated AR is a dirty pig that I found will jam when it gets too nasty. I hear piston operated ones have all the reliability of an AK47. So if I eliminate the one thing I hate from the gun it should be one of my favorites.

  7. A couple months ago a neighbor (Ira) showed up at my cabin with a crosman 38T in the original box with all the paperwork. “It won’t hold a charge, do you know anyone that can fix these” he said.

    I’m not a CO2 guy but have read B.B.’s mantra about pellgunoil for years.

    I bought a bulk pack of CO2 cartridges and a tube of pellgunoil and took it up to my cabin the following weekend. Took about 6 CO2 cartridges and 20 drops of pellgunoil but the gun finally quit leaking. Ira thought I was an airgun genius.

    Gave him the remaining CO2 cartridges and pellgunoil, told him to put a drop on each cartridge before installing, keep the gun charged and thank Tom Gaylord.

    Heard him shoot his 38T last weekend.


  8. Bulk fill guns such as this one are not sold anymore are they? I can’t remember seeing one and do not own one. However, it is great to know this solution for when one of my powerlet pistols starts to leak. This trick is certainly a pistol saver.


    • G&G,

      There are some target pistols from the Czech Republic that are bulk-fill, but I think the regular sporting pistols have all gone away. But there are piles of used bulk-fills available at airgun shows and online.

      I’m going to start the report on the 116 pistol on Friday, and I will include a lot of history for you.


  9. B.B.,

    So might this be a solution, or Pellgunoil, for my P17. Because this gun had caused me so much grief, I hadn’t shot it in years. Well, I tried it last week, and I had to cock and shoot it 2 to 3 times just to get the pellet to exit the barrel. The gun has very little power, and it ain’t from use.


    • Victor,

      I got a P17 from PA last week. The reviews on the P17 mention a problem with a burr on the inside of the compression cylinder nicking the o-ring on the piston. This would account for your problem, and Pellgunoil will not cure it. The O-ring is a standard size found at hardware stores. To correct it, drive out the pin that connects the piston to the cocking linkage and pull the piston out. The intake port should be on the bottom of the cylinder.

      The cylinder is made of aluminum. The burr can be removed with fine sandpaper or Emory cloth. Then the lube should be washed out and the cylinder re-lubed with white lithium grease. This should correct your problem.

      I bought this gun half-expecting to encounter this problem. I even bought a tube of this grease. But as of today, I’ve put 275 rounds through the gun, and I think if the seal was being cut, it would have failed by now.

      The cylinder is greased with an over-generous of black moly grease at the factory. It tends to get all over everything when loading. I wiped off the excess with a cloth, and will re-lube it with the white grease when it needs it.

      I wrote a review of this gun on the PA site.

      The first 30 shots I used Daisy wadcutter pellets. They were hard to load and didn’t group well. Switching to RWS Superpoint Extra pellets solved both problems.

      The P17 is a lot better gun than the price suggests. It is very simple mechanically, hardly anything to go wrong with it, and pulling the piston is straightforward and easy with no little parts to fly about and get lost. Please try this fix before giving up on it.


      • Les,

        Thanks for the info! I’ll take a look to see what’s going on with mine.
        The P17 was the first airgun I had bought in decades. In fact, I bought it before I found this blog, or PA. There were several things wrong. The scariest being that it would fire when closing the top.

        I must say, aside from the numerous problems that I’ve had with mine, I like the feel, I like the rear fully adjustable sight, and the accuracy, when it worked.


  10. Well , it works. I used the same brand stuff that BB used on a leaking 150 (valve stem seal leak, CO2 was blowing out the barrel). First attempt it wouldn’t seal but was able to fire the pistol several times before all of the cartridge was exhausted and distribute the oil/ sealer. Second time was the ticket, but I left the gun ( leaned muzzle up) to warm up in the sun before firing it the first time . Temp was about 75-80 degrees here . When I first tried it the gun had been on my work bench in the basement where it is around 65 degrees. I just dribbled a few drops in the air tube and wet the end of the CO2 cart before installing it. Will see if it seals next time. Great tip!

  11. Hey guys first post here, though i’ve been reading the blog for some months now. Anyways since the subject here is seals it fits my question well. I have a remington vantage 1200 springer that has a nick in the piston seal. It occurred when removing the spring/piston assembly for cleaning and i forgot to back out the scope mount set/pin screw. So after much searching i can’t figure out which piston seal to buy. I know the model i own has been discontinued but seeing as it’s a crosman there should be the same/similar parts in other models still offered. I have been to their web site and the part is not available there, and with all the options i’m a bit unsure which piston seal to buy, and would rather not have to buy a variety to figure out which one. I’m hoping that with the accrued knowledge here someone will be able to point me in the right direction. Thanks for your time and help.

  12. I have an old sheriden pump pistol that leaks, should I use pell gun oil & or ATF STOP SEAL, why don’t hall sell like 5ox bottles of the stuff.
    FYI I have a .20 sheriden silver streak rifle that I bought new at western auto in 1959 at age 11yo, still shoots hard & straight
    love it

    • David,

      Welcome to the blog.

      Go in progression on this. Start with Pellgunoil first and if it doesn’t solve the problem, then try the Stop Leak.

      No one sells small bottles of this stuff because there isn’t that much demand for it. If there were, the product would be sold that way.


  13. BB
    You pointed me to this article in response to to a reply I posted in your crosman 160 blog. While reading it a question came to mind and i read thru all the replies and didn’t see mention of it. I can’t help but wonder about long term effects of the sealer. After all, it is a sealer. It seems to me that it may collect and gunk up in the valve. Anyone experienced any ill effects like this?

    • Bill,

      I have been testing this on plain buna o-rings for the past 3 years. They are still in perfect condition — not swollen, nor brittle. They are still very supple after being immersed in the fluid for 36 months. I will write a blog about it this coming week.


  14. Tom;
    Great news !!!
    I got the gun out this morning and opened it up. The secret sauce did the job. The stuck cart fell right out. I added 20 or so more drops of SS and charged with 2 new carts. Mind you, it’s only 50* in lower Alabama today but the gun shoots very strong. I shot it about 45 times and it hasn’t dropped any power yet. It’s standing back in the case now to see if it leaks off. If that happens, I’ll put the Bars Leak in it. I got a good look at the metal today and it’s pristine. I think the scuffs on the stock will buff out. The Crosman site says the wood is walnut. I have a Birchwood and Casey resttable flipper target set out at 45 yds. No problem plinking them up and knocking them down. I’m sure it will do even better in 72* weather. The trigger seems to be set already for a nice crisp short break but, I’ll clean it up and moly paste it any ways. A fine example of what Crosman is capable of producing. I sure wish they would realize that. I would certainly pay the extra money for the quality. Until that day, I’ll add this one to my other 60 – 70 vintage airguns and continue my search for the next one.

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