Back in the 1950s the father and son team of G. V. Cardew and G. M. Cardew published the results of an interesting study in which that proposed that a large part of the power of airguns came from the combustion of lubricants in the compression chamber of spring-air guns. Thier experiment was simple, and convincing: They fired a .22 cal Weihrauch HW 35 that had been purged of air and filled with nitrogen. Muzzle velocities obtained were significantly lower than when the gun was fired in air.
I’ve always been somewhat distrustful of the Cardews’ experimental methodology, which involved placing a gun in a plastic bag, pumping out air, and bleeding in nitrogen, and then opening the bag and firing the gun, but I’m willing to believe it worked, and that they obtained the results they published. Certainly these guns were burning part of their lubricant; anyone who’s owned a Daisy BB gun is familair with the wisp of smoke and the smell of burning oil that follows a shot from a well-oiled gun.
The airguns of the Cardews’ era had leather piston seals which had to be fairly well saturated with lubricant in order to provide a good seal. Some of this oil would invariably be sprayed into the barrel in the form of a very fine aerosol on firing, and that aerosol would in turn be ignited by the hot air coming through the transfer port, and that would add to the propulsive power of the gun.
But there would also be lubricant burning in the compression chamber- and that should interfere with propulsion, by setting up a shock wave that would drive the piston back before maximum pressure was built up in the barrel. I have, on a number of occasions, encountered just such a situation in guns in which some combustible material- usually a pellet lube or cleaning solvent- has gotten into the chamber. The result is usually a loud report, a blackened (and sometimes ruined) piston seal, often a damaged mainspring, and a drop in muzzle velocity.
And there’s another issue. But in the 1960s, Ladd Fanta started experimenting with using silicone oils- which do not burn- in place of the combustible hydrocarbon oils traditionally used in air guns. Airgun dealer Robert Law also began promoting the use of these new lubricants. And looking over some of the catalogs that Law produced back then, no where does he mention any loss of velocity from using silicone based lubricants. So I remain- let’s say- skeptical, but open to being convinced.
Whether or not the Cardews’ test showed what was claimed, the results still have no applicability for today’s guns. Modern airguns- which the possible exception of some of the very cheapest Chinese guns still sitting in a warehouse somewhere- don’t use leather seals. Any lube beyond a fraction of a gram is quickly shot out. Modern synthetic lubes are made of silicone- a tightly bonded silicon-oxygen molecule that simply will not burn. And despite using only a miniscule amount of lubrication, and being fired regularly for years or decades without any additional lubricant, today’s spring airguns commonly achieve muzzle energies and velocities unheard of in the Cardews’ time.