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Ammo Diana model 60 recoilless target rifle and HW 55CM: Part 2

Diana model 60 recoilless target rifle and HW 55CM: Part 2

by B.B. Pelletier

Announcement: Brendon Krahn is this week’s winner of Pyramyd Air’s Big Shot of the Week on their facebook page. He’ll receive a $50 Pyramyd AIR gift card.

Brendon Krahn is this week’s Big Shot of the Week. He’s sniping at starlings with his .177 Remington NPSS.

Photos and test results for the Diana 60 by Earl “Mac” McDonald

Part 1

The Diana model 60, which is a Hy-Score model 810 in this case, is a breakbarrel target rifle from the 1960s and ’70s.

That’s right, sports fans, today you’re getting a twofer. For the benefit of our readers outside the U.S., a twofer is slang that means “two for the price of one.” I decided to report on both Mac’s Diana 60 velocity test and my HW 55 Custom Match velocity test for reasons I will explain in each part. Grab a large cup of coffee and an extra Danish and sit back!

The Diana model 60 target rifle

We’ll look at Mac’s rifle first. Today, I’ll reveal the one thing that’s been troubling Mac about his rifle, so it doesn’t take a detective to know that it has to do with velocity.

The cocking effort of his breakbarrel rifle is 28 lbs., which seems high to me. Mac says it doesn’t feel that high because, for some reason, it gets lighter toward the end of the cocking stroke. He also cautions us to beware of the rack-and-pinion noises that these guns have when they’re cocked. To all that I have to say this.

There shouldn’t be any noises when this rifle is cocked. I’ve owned several Giss-system rifles and pistols and shot a lot more, and none of them made any extra noise when they were cocked. That’s clue No. 1. And, I’ll explain how the Giss system works next.

Clue No. 2 is the lighter cocking effort toward the end of the stroke. That’s atypical for a breakbarrel, but Diana has the reputation for breaking mainsprings. When they do, they get smoother. They don’t make any noise, nor do they bind during the cocking stroke. I’ve certainly seen a half-dozen Diana rifles with broken mainsprings and they all acted this way.

How the Giss contra-recoil system works
The Giss contra-recoil system consists of two pistons connected to each other. The real one goes forward when the gun is fired, and a dummy travels to the rear at the same time. The real piston is the only one that has a piston seal, and it’s the one that compresses all the air for the shot. The dummy piston has no seal and is just there to provide an equal and opposite reaction to the real piston. When the real piston slams to a stop, the dummy piston does too at the same instant. The EFFECT of this is that the impulse of each piston cancels the other. The first time an airgunner experiences it he’s usually blown away because, when the gun is timed right, absolutely no firing pulse can be felt.

Of course, timing is the principal concern in a gun that uses the Giss system. That’s why I never recommend a person try to repair his own gun. Sometimes, a mechanical genius like Nick Carter who writes Another Airgun Blog will be able to dive right inside a Giss gun and find no obstacle he cannot understand and overcome, but the average person will just create a basket case.

Looking straight down on the top of the model 60 action, we can see the two telltale caps that cover the gears connecting the two pistons to each other. All Giss-system guns have these caps.

This simple graphic shows how the two pistons oppose each other.

Velocity test
I’ll tell you right now that Mac experienced lower velocity than he expected from this rifle. An Air Rifle Headquarters catalog (the original company) from 1973 gives the velocity of the model 60 as 546 f.p.s., without specifying what pellet was used. That would probably translate to about 550-570 f.p.s. with the pistol-weight target pellets we use today. Mac wasn’t getting that.

He asked me what I thought about putting a drop of silicone chamber oil through the air transfer port to lubricate the piston. We know that these older target spring guns came with seals that dry-rotted over the years, and chamber oil will speed up their demise, but I figured he had to find out somehow, so he did it. But it didn’t cause the seal to destroy itself. It simply boosted the velocity about 12 f.p.s. with no change in how tight the velocity spread was.

The first pellet he tried was the H&N Finale Match Rifle pellet that weighs 8.18 grains. They averaged 457 f.p.s., with a 22 foot-second spread from 445 to 467 f.p.s. The average muzzle energy was 3.79 foot-pounds.

Next, he went with a domed pellet. JSB Exact Diabolos are domed pellets that would not normally be fired in a target rifle unless the target was something other than paper. But Mac also uses his target rifles for mini sniping, so he tested this 8.4-grain pellet anyway. It averaged 474 f.p.s., with a 16 foot-second spread from 465 to 481 f.p.s. The average muzzle energy was 4.19 foot-pounds.

The final pellet Mac tried was the old standard RWS Meisterkugeln pistol-weight wadcutter. Today, they only weigh 7 grains, but Mac had some older ones that weighed 7.7 grains. They were a very loose fit in the breech and averaged 458 f.p.s., with a whopping 37 f.p.s spread from 442 to 479 f.p.s. The average energy generated was 3.59 foot-pounds.

Both Mac and I think the rifle isn’t performing up to spec. Mac found some stated velocity figures of 460 f.p.s. in print somewhere, but he thinks it’s a transposition of 640 f.p.s., which is where a few of the 1960s and ’70s-era target rifles were.

I now believe the rifle has a broken mainspring. Mac thinks it’s just a tired one. Either way, the thought that his gun isn’t performing up to snuff is getting under his skin, so I advised him to have it repaired by either Pyramyd AIR or Umarex USA so he’ll know for sure.

Nevertheless, the rifle still shoots as it should and there will be a part 3 coming soon. Let’s go to Part 2 of the other target rifle on today’s menu.

The HW 55 CM target rifle

Part 1

Is this Custom Match the best HW 55 ever made? Read the report to find out.

I’m putting this additional report here for a couple reasons. First, I didn’t want to go too long without reporting on it. More importantly, I thought I might have to do an extra report on this rifle. As luck would have it, that’s how it turned out. While this is Part 2 and a velocity test, the next part will also be about velocity.

Remember that the HW 55 CM was the rifle that I felt had a harsh firing cycle back in Part 1. After I tightened the stock screws, some of the harshness went away. Even after that, the rifle was still feeling harsher than I felt it should for what it is.

Several of you readers thought that when the gun went back to Beeman for a rebuild, they probably installed the upgraded HW 50 sporter mainspring that would have boosted the power. The only way to find that out is with a chronograph, so that’s what I did. According to Air Rifle Headquarters catalog data, once again, a regular HW 55 should shoot H&N pellets at 650 f.p.s. Unfortunately, they don’t give a lot more data about the specific pellets they used for the test.

The rifle does still shoot a little harsh. When you’re peering through a peep sight, the smallest recoil becomes instantly noticeable. In this rifle, it’s unpleasant. The peep comes straight back and bumps into my skull when I fire. My Ballard rifle does the same thing, only its peep is on a tang sight that collapses forward when it contacts my eye. The HW 55 sight, in contrast, remains rigid and allows me to absorb all the impulse of each shot. Well, I’ll be danged if I’m going to put up with that!

The plan is to quiet the shot cycle with black tar, if possible. If the gun has extra velocity it doesn’t need, I’ll be only too happy to do that.

The cocking effort is just 20 lbs. on the nose, and the ARH catalog says to expect a weight of just 15 lbs. There’s another small deviation from what would be expected. Even the HW 50 mainspring isn’t that powerful, and the long almost-18.5-inch barrel may be providing the extra leverage to reduce the force.

The first pellet I tested was the RWS Hobby, that standard candle of high-velocity lead pellets. At just 7 grains, it’s not only light, but often it turns in surprisingly good results downrange. Hobbys averaged 694 f.p.s., with a 17 foot-second spread that went from 684 to 701 f.p.s. The muzzle energy is 7.49 foot-pounds. I would love to say that this speed wasn’t expected, but it wasn’t far enough out of line to be definitive.

Next, I tried H&N Finale Match Pistol pellets. They weigh 7.56 grains. They averaged 632 f.p.s., with a 14 foot-second spread from 625 to 639 f.p.s. The average muzzle energy was 6.71 foot-pounds. That seems right on the money for a stock mainspring.

The final pellet I tried was the RWS R-10 Match Pistol pellet. Although they’re just as light as the Hobbys, they go the same speed as the heavier H&N Match Pistol pellets. That would indicate a bore-fit issue.They averaged 632 f.p.s., with an 18 foot-second spread from 619 to 637 f.p.s. The average muzzle energy was 6.21 foot-pounds.

I can’t tell for certain that the mainspring has been upgraded, but I do know that the rifle has way more velocity than I need. The next step is to lube the spring with black tar to see what EFFECT, if any, that has on the shot cycle. While Mac wants more velocity, I’m looking to get rid of some for the sake of smoothness.

I’ll break these two reports into separate reports for their respective accuracy tests. But before I do the accuracy test with the HW 55 CM, I’ll lube the spring and retest the velocity results, giving this rifle one extra report.

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.

64 thoughts on “Diana model 60 recoilless target rifle and HW 55CM: Part 2”

  1. BB:
    BOGOF (Buy one get one free) is the term we use mainly.

    I remember back in the 80’s when the Saxby&Palmer Orion six pistol came out,some pundits thought it would make all the other spring target pistols redundant(even the HW45).What with the Orion being totaly recoilless due to the use of the air cartridge system.
    Twenty odd years later the HW45 is still pretty much top of the tree.
    Goes to show,you can’t keep a good spring down 🙂

    Thanks for the reference to John Bowkett BB.There is a hell of a lot written about him and his work in Britain.

    • Dave,

      I remember the Orion. I almost bought into the whole tandem air cartridge thing, because the guns were certainly realistic. I have tested several of them and fired many others. I found the guns quite accurate and very well regulated, but filling the cartridges with air was exactly like reloading, only it took too long. I never had the six-cartridge setup that was run by a scuba tank. I always used either a Slim Jim or that horrible pump Saxby Palmer first offered that you could operate with your foot.

      I remember the old Ensign rifle that used the huge plastic cartridges. That one was a real chore to make ready. You can still buy them in like-new condition because everybody who buys one shoots it about ten times then sells it.

      Of course those days are over and the TAC are now collectibles in their own right.


      • BB:
        I found it quite labour intensive giving 5/6 cartridges 8 pumps each only to shoot the lot as fast as I could pull the trigger.
        The temptation to let rip was just too great.

        My pistol is gone now but I still have a box of 5 BACS(Brocock Air cartridges) and a Slim Jim pump knocking around.

      • DaveUK

        When I was in England I think I remember several Britons telling me to BUG OFF. (At least that’s what I think they were saying) What friendly folks!

        • SL:
          Did those Britons who swore at you happen to be wearing ‘London Transport’ uniforms?
          My brother was slung off a train once and he was an off duty train driver at the time.
          A very tough crowd to please them LT staff.

          • DaveUK

            Only being cheeky of course. In my travels through Europe (England, France, Italy) the Brits were the most welcoming of all. I thoroughly enjoyed my time there, I won’t ever forget it.

  2. Well,

    I am very pleased, as I’m sure AlanL is, to see the EFFECT that yesterdays grammar lessons have had on you and how they have AFFECTED you. Well done, BB! Liked your slight poke at those would be grammar police.

    Fred PRoNJ

    • Fred,

      I’m glad we have extra eyes reviewing the blog.

      It’s not that I don’t know the rules of proper/correct grammar, punctuation & spelling…I honestly don’t have the time to devote exclusive attention to proofing the blog. I’m usually breaking away 15-20 times during proofing sessions to answer the phone, peek in on a webinar I’m supposed to be attending, or answer urgent or import emails or gchats. I’m not above stopping a couple times to pet meowing kitties or toss a play mouse for them 🙂

      The blog is written by Tom and quickly proofed by me. A one-time read-thru is all I give it. Half the time, the only time I’ve got is when I’m trying to wind down from a day’s work and watch a bit of TV in the evening. Then, I just read the blog during the ads or when watching a movie I’ve seen many times before. Not ideal, but that’s the best I can do with the workload I shoulder.

      I’m always happy to correct a typo brought to my attention.


      • Okay, I just gotta mention this.
        Two different grammar websites I checked both say that the proper wording is, “the grammar police ARE much pleased’…doesn’t matter whether you’re using the singular or plural of the word ‘police’.
        😉 😉

        • Figures ole’ CSD would catch us out on that one, and here I wondered why the plural of goose is geese but that of moose is not meese. And for mouse it’s mice but for house it ain’t hice! Oh sorry, “isn’t.”
          CSD, go back to your cameras won’t ya, for crying out loud…

          • Okay Alan, just let me get this straight.
            You can point out other peoples errors, but heaven forbid you get caught??
            Or am I reading the ‘go back to your cameras’ crack wrong?

                • See, this is one of the things I hate about the ‘net (actually it’s 1 of about 42 things I hate).
                  Sitting across the table from each other, with a pitcher of beer between us things wouldn’t get taken the wrong way.
                  That or we’d be too drunk to notice 😉

          • Goose/geese, mouse/mice that’s easy stuff.
            You want hard, come take a few french lessons… I was born in it but I still make mistakes in writing, I think I make more grammatical errors writing french than english. I’ve been talking french twice as long as I do english yet it doesn’t show to much in writing.

            I think the hardest part of french for foreigners is getting used to everything having a “sex” and getting to learn the synonymous words, in english you’ll often have one word describing several things, french as several words describing one thing.


            • J-F

              I read somewhere that the Eskimos (or is it the Innuits?) have over a hundred words for different types of snow, but no one word that means simply “snow.”

              • At the end of the winter (march) we gotten enough snow and sometimes refer to it as “white $h!t”, wonder if they have words for the temps being too hot or air conditioning?


  3. Edith,

    we ALL appreciate the amount of work you put into the blog.

    I was just trying to show appreciation to Tom on his capitalization of the word ‘effect’ in today’s blog as a subtle “so there” to the grammar police of yesterday. Actually, until Aaron posted the acryonym “R.A.V.E.N”, I wasn’t sure either when to use affect or effect.

    Fred PRoNJ

    • twotalon,

      I remember them well. That was a toy I never had. I was a few years too old for them when they hit the market, but I always wanted one.

      I was just getting into BB guns at the time. My Fanner 50 was a Crosman SA-6.


    • I had the SA revolver and holster, and a rifle that was a copy of the Colt revolving carbine. They shot a little grey plastic bullet that you reloaded by pressing them into little brass cartridge cases that had a little spring inside. You stuck the caps on the end of those little fake cartridges. The round stick-on caps we had weren’t green but red, as were the tape kind. My father accidentally ran over my rifle with his chevy sedan ,because I left it leaning againist the back bumper. Lesson learned early, don’t leave guns leaning on vehicles! Dad glued it back together but it never worked well again. Wish I still had them ,as I see that they are now worth some money from toy collectors. I was the eldest of seven and toys were handed down and played with hard until they wore down to nuthin and evaporated.

  4. It would seem that a strange version of the Grammar Police is active in the UK where they don’t like the way Americans speak our version of our not-co-much-in-common language. Sounds to me like a deep inferiority complex coming from London and surroundings.

    [From the BBC website:] Our recent piece on Americanisms entering the language in the UK prompted thousands of you to e-mail examples. Here are 50 of the most e-mailed.

    I never bother to tell the British how silly we think it is to call a trunk a boot, etc.


    • They make fun of us calling tissue paper Kleenex, while we make fun of them Hoovering out stuff when they’re really vacuuming. Goes both ways I guess. 🙂


    • PZ:
      The pro European Union BBC did that piece?
      Well I never…There’s your problem.
      It sticks in the throat for them that the majority of folk in Britain can’t be bothered to learn a European language but instead continue to adopt the ways of our North American cousins.
      When is ‘Denny’s Diners’ coming to the UK? That is what I want to know 🙂

      • Dave,

        I wouldn’t hope for Dennys Diners if I were you. In my experience there are two kinds of Dennys, just as there are two kinds of McDonalds. There are the good ones where the food is great and you want to come back and there are the ones where everything is disgusting.

        The only Dennys Diner I ever ate in (here in Fort Wort, Texas) was one of the latter. I had hoped for a great experience and went away wondering if I needed a tetanus shot for just being inside.

        Best McDonalds I ever ate in was the first one built in Nuremberg, back in the early ’70s. I’d been in Germany for two years and it was a taste of home, only the German owners did everything right. You could even get a beer, which made the experience much better.

        Worst McDonalds was in Silver Spring, Maryland, a suburb of Washington D.C. The restaurant was an apology for food, just as the neighborhood it was in was an apology for humankind. I believe it was the training ground for workers who will be hired by the McDonalds in hell.


        • DaveUK

          There are better restaurant chains in the US than Denny’s, but it ain’t bad either. Recently they had a bacon promotion where they were putting bacon in ice cream sundaes. (seriously)

          Of course any restaurant is only as good as its manager.

  5. Wow, I’m kind of impressed that NOT ONE of the preceeding comments has the first thing to do with the Diana 60 or HW 55!!! 🙂 🙂 Just kidding…

    B.B., I will post some more detailed comparison velocity numbers from home later this weekend, but my first impressions are:

    1. Yes the Diana 60 probably does have a broken or very worn springs. These guns will easily exceed 600 fps with light pellets with fully healthy innards, in my experience.

    2. The HW 55 CM is shooting very strongly, I’d guess it probably does have an HW 50 spring. I have one 55 with a 50 spring, and several with aftermarket kits, and none have quite hit that mark with Hobbys.

    Again…more later.

    • COMPARISON VELOCITY NUMBERS as promised above…!

      First a brief word about my testing method–the numbers below are the results of 15-shot strings through an elderly Chrony Alpha. The average velocities and standard deviations are as computed by the Chrony. For each string I’ll list: pellet; weight in grains; velocity in FPS; and standard deviation, expressed as a percentage of the average velocity (IMHO, the best way to compare guns of different power levels).

      Diana 60 no. 1
      A 1967-built “Hy-Score 810M,” rebuilt in 1999 by Tim Challener at RWS in New Jersey. I strongly suspect this rebuild retained the original springs, but new seals were installed. Based on correspondence with other owner, etc., these are typical velocities for Giss Dianas with a bit of mileage on them.
      RWS Hobby 6.9 gr, 567 fps, 0.87%
      Lapua Pistol 7.2 gr, 574 fps, 0.58%
      JSB S100 8.2 gr, 547 fps, 0.47%

      Diana 60 no. 2
      A 1982-built “RWS 60” with Tyro stock, rebuilt in 2005 by Randy Bimrose. All new springs and seals; Randy commented this was one of the “hottest” Giss Dianas he’d seen.
      RWS Hobby 6.9 gr, 666 fps, 0.78%
      Lapua Pistol 7.2 gr, 637 fps, 1.11%
      JSB Match 8.0 gr, 592 fps, 2.16%

      HW 55 no. 1
      An early-90’s Tyro model, with OEM target spring and a Beeman shop supertune. I’ve never had this one apart but I suspect it has a plastic piston seal.
      RWS Hobby 6.9 gr, 651 fps, 1.39%
      RWS Superdome 8.3 gr, 575 fps, 0.45%
      RWS Meisterkugeln Pistol 7.7 gr, 587 fps, 1.89%

      HW 55 no. 2
      A late-80’s HW 55 MM, with HW 50 spring and OEM leather piston seal.
      RWS Hobby 6.9gr, 676 fps, 2.30%
      RWS R10 Pistol 7.7 gr, 622 fps, 1.38%
      H&N Match Hi-Speed 7.5 gr, 640 fps, 1.27%

      HW 55 no. 3
      A Burgo-marked HW 55 M from the early 1960’s, with a recent-production Jim Maccari kit driving a plastic seal on an adapter screwed to the OEM piston. I will never be mistaken for a pro tuner mind you, but darn if this one didn’t somehow end up as a wonderful, smooth shooter.
      RWS Hobby 6.9 gr, 651 fps, 1.39%
      RWS Superdome 8.3 gr, 575 fps, 0.95%
      RWS Meisterkugeln Pistol 7.7 gr, 587 fps, 1.89%

      HW 55 no. 4
      A late-80’s action with an older Maccari kit driving the recondition OEM piston seal. This one is about my favorite shooter of all…
      RWS Hobby 6.9 gr, 696 fps, 0.79%
      JSB Express 7.9 gr, 675 fps, 0.44%
      Eley Wasp 7.3 gr, 692 fps, 0.38%

  6. BB: Some triva you might be interested in that I gleaned from my library . In my only copy of an old Air Rifle Headquaters newsletter / catalog circa 1966 ,they list the H&N ,177 cal pellets wts. on page 26. The Brimoco Match were 7.932 grs with a spread on total wt between pellets of 0.05 grs, and the H&N match were 8.024 grs with a 0.04 gr total wt spread. These were mentioned as the pellets used in your gun and some others like the Walther as then sold by Robert Law. Almost all the pellets that were mentioned throughout the flyer had wts that varied from 7.495 grs for Lion diablos, to 8.561 grs on the high side for the Lion ZET’s. An accurized (?) 55N was mentioned as getting 763fps at 3 feet with the ZET pellets , An Oehler cronograph was used to record the result.

  7. it gets lighter toward the end of the cocking stroke. He also cautions us to beware of the rack-and-pinion noises that these guns have when they’re cocked.

    Given that description I’d be looking for a stripped gear with the result that the countermass piston is only partially cocking — which would also explain a lighter effort on the latter half, if only the main piston is compressing the shared spring while the other moves a bit, jumps a tooth back, moves a bit, etc. Full force would be felt when both pistons are still moving in sync and compressing the spring from both ends.

    • I hasten to say that I am NOT an expert mechanic, especially for these complex double-piston rifles–but I’m fairly sure that what you describe is not physically possible.

      Remember the gun has two controller cogs, each of which engages both pistons; so it would require a strange confluence of several faults to cause any differential displacement of the pistons.

      As for cocking effort, I have two model 60’s and just now fired each one a few rounds. They do have the odd sensation of a perfectly uniform effort being required throughout the cocking stroke–it really does not seem any harder near the end. I also noticed that the more powerful of the two seemed quite a bit easier to cock!

      • My mental image is that each piston has a rack on one side (top or bottom) which mates with pinions; the opposing piston would have the rack on the opposite side. {poor ascii art forthcoming}

        |++++++++++++++++ |
        | * |
        | ++++++++++++++++|

        If the teeth on one of the racks, partway toward the head of the piston were stripped, or the rack bulged outward enough to disengage the pinions, that piston would make nasty noises while cocking as the rack kept slipping over the pinion teeth.

        side observation
        Has anyone ever tried designing one of these actions using real pistons at both ends, with a high-pressure tube connecting the rear of the action to the front just behind the transfer port to the barrel?

        Seems that would give it a much higher pressure level for the shorter piston throw…

        • As I was afraid — the spacing got stripped out, lets try with some other characters in place


          * = pinion
          + = rack
          | = piston head
          . = void space

          • Wulfraed, here’s a link to a nice drawing of the model 60’s action from Chambers in the UK. As you can see, both pistons have an extension with a “rack” on both sides, engaging both controller cogs:


            Gerald Cardew’s classic 1976 book “The Airgun from Trigger to Muzzle” is totally devoted to the internal physics of spring-piston airguns. It convincingly showed that a typical mid-powered springer really only moves enough air to accelerate the pellet for 7 or 8 inches down the barrel. So your admirable idea for a super-long rear piston transfer port, would probably add only negligible boost unfortunately!

            • Said exploded view just confirms my mental impression — on piston has a rack on top, the other has it one the bottom… The fact that there are pinions on both sides is just to let the spring occupy the center… And does nothing to negate that a piston rack with a bad tooth (going all the way across, not just one edge, or arched rack) could produce a nasty noise and reduced cocking force when it slips against the pinions.

  8. Oops! My bad. It won’t work. I tested it out on my browser but it won’t work from here. Maybe because I’m already logged on to Google. Maybe I can make it available another way.

  9. I wonder if the Diana 60 would have gotten better velocity if they’d made the dummy piston a real one and piped it in parallel with the main piston. Kinda like Whiscombe’s.


    • Dave,

      Because of the length of this report I avoided referring to Whiscombe’s design, but of course you are right. Instead of a dummy piston going away from the real one Whiscombe has two active pistons coming together like the clapping of hands. That’s where he gets all his power.

      Our reader, duskwight, is building that kind of gun right now. Let’s all pray for his success.


    • /Dave, the actual Giss patent was for an arrangement exactly as you describe–i.e., Whiscombe-style converging pistons. But Diana opted for the diverging arrangement instead, no doubt more easily adapted to the architecture of their existing guns and production machinery.

      Actually the system does have one advantage that is not often discussed–while the gun may have the compressed air from only one piston for power, it employs momentum from both of the heavy pistons, which on a low-powered gun reduces “piston bounce” to near-zero. The power produced is thus quite efficient with respect to the low cocking effort and small swept volume of the system.

      • Diverging also seems like it might be a little easier to design a release mechansim that won’t have to deal with long reaches and the part’s flex that comes with that. In other words, it might be easier to get the pistons to release at exactly the same time, which would do a better job of cancelling out the recoil and vibrations caused by a slight mis-timing.

        • /Dave, you might find this interesting–it’s the original Giss patent drawing:


          As you can see, one disadvantage of the “converging” system is that the controller cog, and the transfer port and barrel, are vertically displaced from the powerplant, requiring a relatively bulky and complex gun to enclose it all. The “diverging” system allows both functions to be in line with the powerplant, and fit within a simple receiver cylinder little different from that of a typical single-piston spring airgun.

          But–in either system, the pistons are connected by controller cogs, thus allowing the trigger to release both of them simultaneously while being connected only to the rear piston.

          • Thanks for the link! That’s going in my favorites. I may not currently have the time to actually build anything, but I really like looking at different designs!

            Thanks again!

  10. There was a *pistol* in Beeman’s catalog using two pistons in the system you describe. This was in the late 80’s or early 90’s.

    640 fps sounds good, that’s right about where we liked to see our mid-90’s olympic guns when we bothered to chrono them.

    Dead starlings FTW only problem with that photo is I can see you.

    • Diana actually made double-piston Giss pistols, before their rifles! The model 6 pistol was first made about 1960, while the model 60 rifle came out in 1963. these pistols have the same frame and trigger as the simpler model 5 pistol, but in the late 1970’s the powerplant was adapted to the awesome model 10 full-race, 10-meter match pistol.

      Beeman sold two versions of the model 6, called their model 800 and 850 I believe, as well as the model 10 which was known as the “Beeman model 900.”

  11. Probably have to batten down the hatches in the wake of the Norwegian massacre. Just a horrible event — and it took place in a country with pretty moderate gun laws.

    • Apparently it was just one guy, deranged. I don’t know if we’ll know what was in his mind, if it even contains any logic at all. It’s not the first time a wacko went wild and won’t be the last time. From what has been reported so far there is nothing “gun control” about it. There is nothing that can protect us from wackos. They are a fact of life.

      • Unfortunately, the usual response to a lone wacko is to try and ban the ‘tool’ he used in his rampage. Has happened in the UK and Finland, nearly happens in the US. We’ll see about Norway.

      • Chuck,
        I wouldn’t describe this guy as deranged. Everything that he did was premeditated, and with specific, directed, harm to the innocent. Unfortunately, in this modern world, he’s not as rare as he should be. Lots of idiots get so wrapped up in their ideology and personal view of the world (thinking that they own the truth) that they are prepared to do similar things. That’s why I sometimes call it IDIOTotology. Then there’s the BS, ultra-shallow, shock-jocks who spend all their time feeding nonsense (and fire) to those who are already so worked up and ready to do their part in ending some “threat” to America, or other country.

        This Norwegian guy was NOT crazy, he was EVIL, plain and simple. We now know more about him, his manifesto, hatred, and fears. The politics of fear continues to thrive throughout the world. It creates instability, and polarizes the masses. It’s classic divide and conquer. So much more to say, wrong place to say it.

        It’s a shame that the worse that can happen to him is 21 years in prison. I hope there aren’t more to follow.


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