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Ammo Airgun standards

Airgun standards

This report covers:

  • Foster fitting
  • Electricity
  • Fill probes
  • De-facto standards
  • Standards that work
  • PCP hookup
  • Ammo
  • Summary

Today I write about a subject that plagues us all — standards. There are so many that it seems as if there are none.

Foster fitting

At the beginning of this month I lamented that the Foster fitting on the first Seneca Eagle Claw rifle I tested was super-hard to attach to. I had no idea that Foster fittings came in many different sizes. Read this Airgun Wire article by Tom McHale to learn more.

I always wondered why some Fosters were hard to attach to — now I know. But the knowing may not help that much!

Foster male
The male Foster fitting that BB thought was universal comes in many incompatible flavors.


You learn real quick when you travel that electricity is different wherever you go. Not just the shape of the plugs that go into the wall, either. In much of Europe, the AC electricity is 50 cycles per second/Hz, while here in the US it’s 60. Does that matter?  Well, your US alarm clock may lose time if the cycles are fewer AND if your clock is running directly on the power grid electricity. One way around this is to put a converter in the clock and convert the power to direct current that the clock then runs on.

It’s not just clocks. Microwaves, coffeemakers, clothes washers and scads of other appliances that use time in their operation also have to be considered. And the problem goes beyond just time. An electric motor that’s built to run on 60 Hz alternating current will run slower on 50 Hz — even if the voltage has been rectified to correct parameters. That’s not good for the motor.

Fill probes

I once had an airgun maker tell me their airguns were made to accept a “standard 8 mm fill probe”. Great! Except for one or two things. First, how long is the probe for their guns? Will someone else’s short probe even put the air release holes far enough into your fill port to get air into the gun?

Also, where are the air release holes located on the probe? Are they somewhere that the air they release has a chance to enter the air intake port on the gun being filled? Or are they out so far that they are on the outside of the gun’s fill port?

I criticize Air Arms for their odd-looking fill adaptor, but given that Foster fittings aren’t all the same I guess it doesn’t make any difference.

Air Arms adaptor
The Air Arms fill adaptor is goofy-looking, but it works.

If you look at the fillers and adaptors for precharged airgun on the Pyramyd AIR website you will find 50 different items.

De-facto standards

There are some things that have become standards just because they were first and people have used them, mostly without complaint. The 1/8″ BSPP (British Standard Parallel Pipe) thread is one example. But there are still problems with even this. The Koreans, for example, don’t make their thread sizes in this nearly-universal size, or at least they haven’t in the past. So there are a lot of fill probes that won’t attach to air hoses without going through another fitting adaptor ritual. As Jefferson Airplane taught us, “One pill makes you larger. One pill makes you small. And the ones that mother gives you, don’t do anything at all…”

Stock up on Air Gun Ammo

Standards that work

Okay, what about standards that do work? Still talking about high pressure air, scuba tanks have a couple standards that are fairly universal. In my limited experience, DIN 200 bar and DIN 300 bar fittings are the same, except for their lengths and the pressures they are designed for. DIN stands for Deutsches Institut für Normung (German Institute for Standardization).The hole in the 300 bar fitting is deeper than the hole in the 200 bar fitting, but the diameter and threads are the same.

300 bar DIN
The 300 bar DIN has a deeper hole than the 200 bar, but the threads and diameter are the same.

Oddly enough, rotary airgun magazines have some commonality across brands. A Marauder mag, for instance, fits several different PCPs. And, when that is the case, usually a single-shot tray will also interchange between platforms.

Marauder mag
Many airgun companies use the same magazine as the Benjamin Marauder.

PCP hookup

Years ago Pyramyd AIR discovered that connectors were a major obstacle to new buyers of precharged airguns. So they created a “PCP Hookup” tab on each PCP main page that shows the buyer what will fill the gun. It’s down by the description. Each of the items in that dropdown page can be clicked on and it takes you to a sub-page of fill devices that attach to the Air Arms Adaptors.

One of these days I will have to write a blog that’s devoted to filling precharged guns, because there are several things to be considered. It’s not just the fill device, but also the input connector and the hose that connects it to the fill device.


No problem with airgun ammunition — right?

Wrong! Just try to load the oversized Marksman BB (diameter of 0.1765-inches) into any normal BB gun!

DON’T TRY IT! I already did and I still have a BB jammed in my 1976 Pioneer BB gun shot tube!!! Steel BBs are 0.171 to 0.173-inches in diameter, and don’t try telling me that a couple thousandths of an inch make no difference. They really do! I have had woodworkers tell me that thousandths of an inch aren’t important, and for projects like building houses they aren’t. But when it comes to ammunition, they really matter. 

Even big bore air rifles come into play on this one. My AirForce Texan loves bullets sized 0.4575- to 0.459-inches in diameter and will not tolerate them smaller than 0.456-inches. That’s why I went to Mr. Hollowpoint for my Texan bullets and I found some that the rifle really likes. 

But there are at least three different sizes of .45 bullets and they either will or will not work in a gun, depending on its barrel. There are 0.451-0.452-inch pistol  bullets that are for the lower-powered airguns. Then there are 0.454-inch bullets that are for Hatsan guns. Finally there are 0.457-0.459 bullets that are for the more powerful air rifles.

I have tried on this blog to help those new to big bore airguns understand the ammo issues. The barrels of the Korean big bores that I have tested, for example, were sized to fit lighter weight pistol bullets. They liked bullets sized 0.452-inches in diameter.

I see that Pyramyd now offers a 166-grain lead bullet that’s 0.457-inches in diameter and that might be good for a test with my Texan at some point. It sure would go fast!

Pellets are a different matter. They tend to fit all airguns of their caliber, though we all do know that some pellets shoot better in certain airguns than others. Years ago there was a small issue with some oversized .22-caliber Eley Wasps that were made large to fit specific vintage pellet guns, but as long as you knew that, everything worked out well.


Standards are in place to make things more compatible, but when they are either disregarded or mismanaged they can make the situation worse instead of better. What are your concerns about airgun standards?

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.

48 thoughts on “Airgun standards”

  1. Talking about standards, some time ago I was wandering about threading types. Trying to figure if 5/16 is compatible with 8mm for example. Any thoughts on this one?
    A good day to you all.

    • Thoughts? Yes, DON’T! Threaded fasteners are a system of male and female connectors. Depending on the application, mixing threads will lead to eventual failure, with catastrophic results.

  2. B.B.

    P P P no longer means Price Point PCP, now it mean Poor PCP People. That is what happens when you take something simple and self contained and make it Complicated, Confusing, and Expensive.

    The Darkside guys at my range drive 3/4 ton pick-ups and they need it with all their gear. Most have wagons to haul it all around the range.
    I just have to worry about not running out of pellets….


    • Yogi,

      Most of the gals here at RRHFWA are sproingers. For years, the only PCPs I had was a Talon SS and an Edge. Those I filled with an hand pump. It was not until I went big bore did I buy a compressor and tank. With them big honkers there is a whole lot of pumping for just a little shooting.

      You grab up one of those .30 Hatsans and we will see how many times you shoot that sproinger.

      • RidgeRunner: I own an Hatsan M-135 in .25 Cal. I think I could manage the same thing in .30 pretty much at will. To me, as an unredeemed springer guy, arm pump up (not to be confused with pumper pneumatics), is just part of the game. I have considered the .30 springer save for: 1.] Do I REALLY need another caliber for which to buy pellets? 2.] Do I REALLY need to spend weeks building a new arms locker at the current cost of fine lumber? 3.] Given the miseries of finding a Hatsan rifle that actually has pellets that obturate (the .25 Cal bore is way over-sized)? 4.] Will the wife find the UPS Box from P/A before I can spirit into the basement? 5.] How will I disguise the credit card billing from my home accountant (c.f. #4 immediately above)? 6.] Finally, now that I have significantly won the war on squirrels and garden rabbits in my suburban home (the 10 M basement range distance just happens to be the distance from the windows on three sides of my house to my property line) do I really need a springer “elephant gun”?

        • LFranke
          As many, here, can attest, first you “want” then you find a way to need. And that goes for pretty much anything,,, but our “toys” especially.

        • Y

          Nice pistols. You obviously like the HW50S air rifles. Mine in .22 is as accurate at 25 yards as my HW30S. I also have the Hatsun .95 Vortek but in .177. The air spring gave out after 4 years and I had Hatsun convert it to steel spring. I have not yet found the sweet spot hold to get same accuracy it gave before. Not bad, just not as good.


  3. BB,

    is there a typo in the size of the Marksman BBs? You say they are oversized, but the diameter you mention (0.1565 inches) is smaller than the one for “regular” BBs (0.171 to 0.173).


  4. The cynical side of me thinks that the manufacturers do this deliberately to make more money on extras like fittings. I only have 2 PCP pistols and aside from the hand pump have had to buy around £50 ($70) in adaptors to be able to fill them.
    Once the fittings are purchased for a particular manufacturer some people will stick with the same brand so they don’t have the hassle of getting new ones, so a kind of enforced ‘brand loyalty’ applies.

    • That seems true also of regular air compressor fittings as well even within the different letter sizes. I have size “N” in my air tool and compressor/hose system. Nevertheless, there seems deviation between steel and brass and even within each.

  5. B.B.,

    I am still so sorry for suggesting those oddball Marksman BBs for your 1976 Pioneer. It’s my fault! :^(

    Have you tried putting a steel cleaning rod in through one side, holdong the whole thing vertically, rod down, on a workbench, and tapping (hard taps) the other end? With penetrating oil?

    Man, I’m so terribly sorry.


  6. BB,

    I have no issue if a new standard is required for something that is truly a (proven) technical advancement over the current standard. I’ll adopt it immediately.

    The flip side is that if a manufacturer introduces a new (proprietary) standard without technical merit I will refuse to purchase the product.

    If the new “standard” is a blatant “forced brand loyalty scheme” I will go out of my way to caution everyone I can away from supporting that product. For myself, I would likely blacklist the company (forever) as I don’t abide companies who take advantage of people who may not know better.

    …sorry, but you did ask 🙂


  7. BB,

    I have encountered different “styles” of Foster fittings with shop compressors, hoses, etcetera when trying to mate things up. Fortunately I have not encountered such with my airguns, though I must admit my “Darkside” experience has been limited to the American airgun companies with such.

  8. I think Airgun Wire article is complaining more about Quick Disconnect fittings not fitting with each other more so than anything else.

    From everything I have seen there is a standard for QDs, and it’s largely being followed, but here are 3 contributors to the issues:
    1. Tolerances are not always followed on dimensions
    2. Equally prevalent issue – if you have a female batch of QDs that errs on the side of closer to the max allowed dimensions, but male batch (from another manufacturer) erring on the lower side of the allowed dimensions there is a good chance they will not work together. Pyramyd AIR is having to help customers with that all the time, and it’s a matter of just reaching our tech. department.
    3. Imperial vs. metric standards are slightly off from each other.

    I understand the argument of proprietary vs. non-proprietary probes, don’t think much can be done there to get industry to the same spot. Think of it as a way for manufacturer to ensure safety based on their tolerance for safety factors – that’s the main reason Air Arms uses their fill adapter approach. They believe it’s the safest one, and I actually tend to agree.

    Well, that’s all you never wanted to know about PCP adapters, right? 😉

    • Val
      I heard something from a cute little birdie.

      PA might start limiting pellet order amounts.

      Sounds like the firearm bullet shortage scenario.

      But if it allows people the ability to get a given amount of pellets to a order rather than a few bunch of people massively ordering and wiping out the available pellets to everybody else I’m for it.

      Its like people pre order right now and those people get thier orders filled and everybody else waits again. And they are massively ordering.

      Hopefully if and when you do it you all will think it out thoroughly to make it more fair to everyone before you implement it.

  9. I think some of the problem with ‘Foster’ fittings is the general imprecision when talking about them. Foster is a brand name of a manufacturer that makes a number of different fittings- series #2 thru #6. The series #2, also referred to as 1/8”, is the de facto norm for ‘Foster’ fittings for air guns. When people start mixing ‘series’ the problems ensue. Now mix in manufacturing differences around the globe and it is easy to see why there are issues. Ask some hard questions of your air gun manufacturer. Are you using genuine Foster fittings, or are you using asiatic ‘will fit (maybe)’ fittings?

  10. “One of these days I will have to write a blog that’s devoted to filling precharged guns, because there are several things to be considered. It’s not just the fill device, but also the input connector and the hose that connects it to the fill device.”

    I’d certainly appreciate a report or series of reports on the topic. I’ve been meaning to get a small bottle or two (buddy bottles?) but the whole mess of fittings and compatibility have gotten in the way.

    Same with getting into CO2 guns. There seem to be various types of cartridges, with differing lifetimes and refilling methods. A good primer would be valuable.

    Perhaps there are others like me who only have 2-3 PCPs and a small compressor and backup hand pump, rather than most of the folks who reply here that have large and eclectic collections 🙂

    And maybe too there are others like me that have a limited budget, but just want to enjoy shooting, without getting too much into the details of crowns and leades and clipping springs and whatnot 🙂

  11. B.B.,

    The fact that QD (Quick Disconnect) is the correct term as Foster is abused just as Kleenex is abused for tissue.

    The most dangerous issue with QD fittings is the lack of knowledge about the various maximum pressure ratings.

    Weaver mount and Picatinny components are not two way interoperable; only one way. Some picatinny STYLE components have entered the marketplace. Picatinny is a very tight dimensional standard.

    What a mess! Interoperability is multi Trillion $ € £ ¥ drag on the World Economy.


  12. As the Russians said to captured German scientists and engineers they spirited East after WWII ended, “we like the way your weapons work; now make them work but simplify!” Or words to that effect. Bet they also meant “make things fit universally or else!”

  13. BB, I have the 28th edition of the Machinery’s Handbook, pretty close to the ‘Bible’ as far as threadforms go. Plus it’s just jam packed with information. Not cheap either. Hertz is the ‘frequency’ setting on a welder. Hertz is also what cause fittings to loosen up, because it vibrates. I have seen Mig welds like that on the HW30s caused by the polarity being reversed too. It took me a while to figure that one out.

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