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Whiscombe rifles and barrel harmonics – Part 1 Introduction

by B.B. Pelletier

Whiscombe JW75 breakbarrel. I know this is a tiny picture; but in the coming reports, we’ll see all the details of this exemplary air rifle.

This report has been a long time coming, but now its time has arrived. It will be a general exposure to Whiscombe air rifles with a discussion of barrel harmonics, because Whiscombe was the only airgun manufacturer who ever sold a system to tune them. I’m doing this report now because of the RWS 54 report. There are several similarities between the two rifles that I think are best discussed when both are in front of us.

Dual opposed pistons
John Whiscombe’s chief claim to lasting fame in the airgun world was the invention of dual opposed pistons that increase power and eliminate recoil in a spring-piston air rifle. The pistons are opposed, which means they’re facing each other. When the gun is cocked, each piston is pulled back against its own separate mainspring. When the gun is fired, the pistons come together…like the clapping of hands. Instead of a closed compression chamber, each piston acts as the compression chamber for the other piston. They come together at the air transfer port, so all the compressed air is squeezed out the port and behind the pellet.

The challenges were the timing of the pistons, getting both to release at the same time, and building a cocking mechanism that applied equal force to two pistons going in opposite directions. Whiscombe solved all these problems and wound up with exactly what he set out to create, a spring-powered rifle that shoots like a PCP.

Every Whiscombe model has a designator that tells you exactly what the rifle is. The initials JW stand for John Whiscombe and the number that follows is the separation of the pistons in millimeters when cocked. So my JW75 has a 75mm piston separation. Greater separation means more swept volume, which means more air to compress, resulting in more power. Other models were designated as JW50, JW65, JW70, JW75 and JW80. There may have been others, but these are the ones I’m sure of.

Underlever cocking
The Whiscombe is an underlever. The smaller models are cocked by pulling twice on the lever, while the 75 and 80 require three pulls. A toothed gear ensures both pistons are withdrawn exactly the same. The mechanism is well-designed and robust, but I get the impression that it’s rather like a bumblebee that, according to aerodynamic engineers, should not be able to fly. I try not to think about it too much.

You are now seeing where few airgunners have ever looked. This is the cocking mechanism of a Whiscombe in action. A geared rod moves each piston in the appropriate direction. The JW75 requires three pulls on the underlever to cock.

Actually, Whiscomes are very robust, but they will not tolerate idiots. If an owner tries to disassemble his rifle without knowing exactly what he’s doing, he’ll break it straightaway. And, the rifle simply cannot stand being dry fired even once. The first one will damage the gun, necessitating repairs. Think about it – two pistons come together and each serves as the end of the compression chamber for the other. The only thing protecting them is the thin cushion of compressed air that stops them from colliding at speed. A dry fire is a head-on collision of the pistons that destroys their seals. A Whiscombe owner must act like the owner of a Ferrari. You operate the equipment within the guidelines set forth by the manufacturer and forget going to Jiffy Lube or Midas Muffler (or Smiling Jack’s airgun shop, in this case)!

To avoid confusion
No, the rifle does not develop less power if you only pull the underlever twice. The trigger does not engage the sear until the end of the third pull. In fact, until you develop the knack, it’s possible to think you have fully cocked the rifle when you haven’t. Yes, it is possible for an underlever gun to also be a breakbarrel. The barrel breaks for loading only, not for cocking.

I’ll cover these points in greater depth in future reports.

15 thoughts on “Whiscombe rifles and barrel harmonics – Part 1 Introduction”

  1. Lama,

    They aren’t cheap! Because each one is hand assembled by John Whiscombe, you are also paying for the time that takes.

    I would tell you the cost, but I want to save it for the next report when I get into the details more deeply.


  2. Diana 75,

    The Diana 75 uses the Giss counter-recoil system in which a dummy piston of the same weight as the real one travels in the opposite direction. They both get to the end of travel and cancel each other.

    The dummy compresses no air, and it travels AWAY from the real piston instead of toward it. So, no, the 75 isn’t like the Whiscombe.


  3. Wonderful article, B.B.

    I have wanted one of these gems for many years. Your article is making me wish I had bought one rather than my latest match rifle.

    So many wonderful air guns.

    A query: Many of us shoot and enjoy firearms as well as sirguns. Yet, airguns hold a certain fascination. Any thoughts as to why? There are the obvious: quiet, “safer”, easier to find places to shoot – but these characteristics don’t explain why they are so fascinating.

  4. BB,
    Just curious, but does the rack and pinion act when firing, or does it retract somehow after cocking?

    In other words, if you took one spring out would both pistons still fire? Not that you’d want to because of the weakness, unevenness and wear which would surely result, but for purposes of illustration, if you fired the gun with one spring only, would the racks and pinion transmit the movement to the other piston?

    Mostly I am just wondering how the gun stays timed even as one or the other spring gets a bit weak, or how both pistons start firing exactly at the same time.

  5. The rack and pinion is only for cocking the gun, not for shooting. The mainsprings drive their dedicated piston. Take one out and the gun is broken. Only one piston would move.

    As for being baffled by how the pistons both fire at the same time, join the club!


  6. The suspense is killing me…..what kind of power does this rifle develop? You said it is similar to a PCP, so that must be well above 30 foot pounds, or more than a Patriot. Does it come in .25, too?

  7. “Rodney Boyce, the man who started importing Daystate guns to America, once told me the fascination is simply that a puff of air can accomplish so much. I think he’s right.”

    Good observation.

    Thanks, B.B.!

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