Whiscombe’s Dual Piston System

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Spring air guns are rugged, reliable, and simple to maintain, but they do have a disadvantage compared to pneumatic guns- as they get more powerful, they get heavier, and larger.  More powerful guns require larger, heavier springs, and heavier pistons- which means more recoil and higher stresses. Spring strength has to be increased not just to propel the pellet, but to move the combined mass of itself and the piston quickly enough to keep lock time reasonably short. There’s a point at which the mass of the combined spring and piston simply makes a gun unwieldy.  It’s difficult to make a spring gun with a power much beyond 22 foot-pounds. But John Whiscombe, one of the true wizards in airgun design, came up with a very clever way of overcoming many of these limitations.

Back in 1987, Whiscombe reasoned that by using two springs, and two pistons, he could increase the power of an airgun without overstressing the parts. And by having the pistons move in opposite directions, recoil would cancel out! Result: A spring air rifle that could achieve muzzle energies of over 30 foot-pounds with zero recoil. The dual-piston system was not original- RWS/Diana used it in the 6G target pistol- but making both pistons active was original. Like the Diana system, the Whitcombe system requires careful adjustment and synchronization to get the pistons moving at exactly the same time. A bit off one way or another and you get a huge loss in efficieny and the recoil returns as well.

About the same time Whiscombe was developing his dual-piston system, Dave Theobald and Ben Taylor of Theoben came up with another, simpler system: Replacing the spring with a cylinder of pressuring gas. Low mass, no metal fatigue, and no overstressed springs. The result was a simple system capable of over 30 foot-pounds without the complexity of Whiscombe’s system.

But even as Theoben’s rifles gained traction in the marketplace, Whiscombe continued making his unique guns. Not only do they have the advantage of zero recoil, but for many airgunners, there’s the simple pleasure of owning a precise, hand-made example of the airgun maker’s art- and owning a rare gun made entirely by hand, and in very limited numbers. If you’re interested in obtaining one of these handmade beauties, you can read more about Whiscombe’s guns here.

Hypervelocity, and Why it’s Bad

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The last few years has seen the introduction of as great number of leadfree pellets, either saboted (as in the Skencos), or cast of an aluminum or zinc alloy. While the idea of lead-free pellets is a good one, their light weight makes them a poor choice in most airguns, for a number of reasons. The first is that a light pellet in a high-powered spring gun doesn’t produce enough resistance to cushion the gun’s piston at the end of its travel. This results in harsh firing behavior, excessive vibration, and very often damage to the spring and piston seal.

While pneumatic guns don’t have these problems, excessively light pellets don’t extract as much energy from pneumatics as do heavier pellets. Light pellets don’t spend as much time in the barrel as do heavier pellets, and as a consequence, more propellant gas is wasted

Both spring and pneumatic guns share a common problem with light pellets: The higher powered guns that are popular today easily push these pellets well past 1000, into the supersonic range, and pellets simply do not perform well at these speeds. Drag goes up exponentially, pellet flight is upset as the shock wave overtakes the pellet a few yards downrange, accuracy disappears, and you end up with poor accuracy and less energy downrange. Skenco explicitly warns that exceeding 900fps will be detrimental to accuracy, which means that these pellets should never be used in guns with more than 12ft/lbs of muzzle energy, if that.

Unfortunately makers have taken to bragging about the excessive velocity obtained from lightweight pellets in their advertisements. For example, I see a new inexpensive Walther rifle brags that it can exceed 1400fps  with the new pellets! But the wise airgunner knows that you should choose your pellets to keep velocities under 1000fps. High powered guns need heavy pellets. If you think you need 1400fps to take small game out to 100 yards, maybe you should be using a .22 rifle instead of an airgun.

Crosman Fireball Pellets

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Crosman Premier pellets are my favorite all-around pellet, as well as the favorite of most airgun field target shooters.  They’re an excellent design, and Premier quality control is second to none- shape and weight variation between pellets is minimal. The .20 caliber Premiers are the best .20 caliber pellet available, period.

But not all pellets with the Crosman name are of the same high quality as the Premiers. Case in point: Crosman Fireballs. These complex looking pellets consist of a lead base with a small steel BB inserted in a hollow point. They’re advertised as having superior penetration, which is kind of silly, as a lead or lead alloy pellet is hard enough to penetrate any game you’re reasonably pursue with an air gun. Adding that steel ball just increases the chance of a ricochet- not a good thing. And steel, being lighter than lead, lowers the ballistic coefficient of the pellet. And should the BB get loose in the barrel, it’ll scratch it badly.

If you look at the photo above, you’ll see what a lot of Fireball purchasers have been complaining about- poor quality control.  Some pellets are constructed off-center, which isn’t going to help accuracy. Others have large amounts of lead flashing still attached. Many are simply malformed.Do a Google search on Crosman Fireball and you’ll find a lot of similar photos and complaints.

Pellets with a steel ball have been around for at least 50 years, and have never quite caught on. They’re more expensive than all-lead pellets, and in every instance I’ve seen, suboptimal. That doesn’t seem to stop manufacturers from marketing them. Besides the Fireball, you can buy Gamo Rockets, and there may be one or two others still on the market I’m not aware of. Should you get the urge to buy a tin out of curiousity, go right ahead. Just don’t put them in the good airgun of yours!

A not at all cheap Air Pistol

Having featured one of the cheapest airguns on the market in my last post, how about one of the most expensive? Switzerland’s Kueng Airguns specializes in custom replacement parts, tuning, precision machining, low volume, and high quality. Pictured is their prototype Magnum Air Pistol, of which they say:

Spring piston design air pistol that delivers the punch of a magnum air rifle; a 12 footpounds* power house! Its unique design incorporates a long-stroke system making this tremendous power possible. No other springer pistol comes even close.

Definitely a project worth watching.