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Cardew revisited… again.

I wrote about this a while ago, but it seems there’s still a lot of this nonsense out there. I just found this on another air gun site:

“Sporting” spring airguns need to combust. “Match” spring guns generally do not. Match air rifles usually yield less than 6 foot pounds of muzzle energy. Adult sporting spring rifles are intended to yield just under the UK FAC 12 foot pound limit, or non-FAC guns generally in the 20 to 30 foot pound class. They all burn oil. Sporting spring guns are tuned for power; Match guns are not. Match spring guns generally work in the “pop gun” phase (re: Cardew) and are not designed to burn any oil whatsoever. That is why Match guns often use steel piston rings that exclude oil from the air chamber.

Exactly when the oils combust depends upon the volatility of the lubricant, it’s mix ratio with the air available and the pressure and temperature exerted upon it. If that sounds a little like a Diesel engine, it is, but with one major difference: the oils in the spring gun are meant to burn, NOT detonate! “Dieselling” in a spring gun is horrifically obvious; the gun fires with the noise of a firearm and sometimes with the smoke of a flintlock! Detonation in a spring gun is to be avoided at all costs; it can cause serious damage to the piston head, spring, and integrity of the gun and may be dangerous for the person holding same! The oil should combust in the transfer port or the breech; if it ignites in the air chamber, detonation may result.

Now that contains at least two pieces of nonsense, and maybe more. At a minimum, it’s horribly out of date. No one shoots spring guns in serious competition anymore. Even beginners are using low-cost single-stroke pneumatics that cost less than the cheapest spring match pistols. And no one is using a combustable oil in their airgun.

Secondly, the author has a common misunderstanding of the term “detonation”. There’s never any detonation in a spring gun- or in a diesel engine. Detonation refers to a condition in which a blast wave moves supersonically through a medium. That happens in high explosives, but not in airguns or internal combustion engines.

Last, modern spring air guns use very small amounst of lubricants that are compounded from ingredients that do not burn at airgun temperatures- usually silicone paste and molybninum disulfide. A properly lubricated modern spring gun can be fired regularly for years without needing any lubrication- this would certainly not be true if the gun were burning a bit with every shot.

The guns in Cardew’s day used leather seals that had to be replenished regularly with oil, as the oil migrated out of the leather, was sprayed into the compustion chamber, and yes, some of it burned. Traditional Daisy BB guns still need regular oiling to keep up their power. Cardew’s experiments claimed to show that this combustion was responsible for a large part of the energy developed. I don’t think it’s a matter of burning oil so much as it is a matter of needing a lot of oil to swell up the leather seal. When airgunners started putting silicone oil into their guns- which doesn’t burn- there were no reports of guns suddenly losing energy.

Unfortunately there’s stil a ton of outmoded or just plain wrong advice still out there, based on repeating old advice, or justy plain ignorance. Take this example from a commercial site:

Oiling the spring chamber and the piston is done only once in a while, about every 300 to 1,000 shots with 2 drops of a synthetic oil (high flash cylinder oil)

I can just see trusting beginners dropping Mobile 1 down their barrels after shooting a tin of pellets and wondering where all the smoke is coming from, and why the gun doesn’t shoot right anymore. And then there’s this:

An airgun is a quirky weapon. Even although it is classified as an airgun, most high powered pellet guns are actually firearms due to the explosion of oils in their chambers that may contribute up to 45% of total power…

The Cardews only claimed 30%; where did this guy get his numbers? I can see someone eventually claiming that 200% of the energy comes from burning oil.

I still see that almost every airgun dealer sells silicone oil and “oiling needles” designed to squirt this stuff into the compression chamber. Unless you actually own an old airgun with leather seals, don’t go near this stuff. And don’t try to lube a modern airgun from the transfer port. The only way to lubricate a modern, synthetic sealed spring gun is to disassemble it, and put a light coat of a proper synthetic lube- like Jim Maccari’s silicone-moly tar- directly on the piston. Anything else is a waste of money and possibly harmful to your gun.

6 Comments

  1. mark wrote:

    After 30 years of firing all manor of air rifles, rimfire and centerfire rifles I have a very good understanding of what makes things go. A high powered air rifle will diesel with the right mixture of light oil and compression. This can break the spring and also causes inaccuracy due to vibration on firing. How ever the only damage to the rifle is perhaps the breaking of the main spring. The velocity increase is notable as is the muzzle report ie with a 22 meteor air rifle, it sounds like a .22 short and will punch a hole straight through a glass bottle.

    Thursday, August 23, 2007 at 3:05 am | Permalink
  2. mje wrote:

    I have also seen damaged piston seals from inadvertent dieseling. Nonetheless, the notion put forth in the quoted article- that modern guns depend on dieseling- is still nonsense.

    Thursday, August 23, 2007 at 6:35 am | Permalink
  3. Nathan wrote:

    Detonation does occur in internal combustion engines. That is what a knock sensor helps prevent. In the automotive spark ignition engine world, detonation is the pre-ignition of the air/fuel mixture which causes a rapidly expanding flame front to collide with the intended flame front originating from the spark plug.

    Saturday, January 5, 2008 at 4:27 pm | Permalink
  4. mje wrote:

    While it’s called detonation, it is not, strictly speaking, detonation, which involves a supersonic flame front.

    Saturday, January 5, 2008 at 6:31 pm | Permalink
  5. Marc DV wrote:

    Instead of poo-pooing Gerald Cardew’s research, please substantiate your claims or keep them to yourself. As a professional engineer for more than 40 years, I found none of Cardew’s claims to be innaccurate and all of them were documented by experiment. Suggest that you do the same – put up or shut up!

    Thursday, June 12, 2008 at 8:01 am | Permalink
  6. mje wrote:

    Did you ever try to duplicate the Cardew’s methodology? I suppose I should borrow a cylinder of Nitrogen and do this myself.

    Thursday, June 12, 2008 at 1:34 pm | Permalink

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