A MATERIAL DIFFERENCE

Replacing old leather piston seals with modern synthetic alternatives? Jim gives it a shot

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Before the advent of synthetic piston washers and ‘O’ rings, piston seals were made from leather and in some ways, it’s not a bad choice of material; it’s readily available,fairly cheap, and flexible enough to form a good air seal without excessive friction, but it does have one major drawback, which is that it dries out and becomes inflexible after repeated shot cycles in the high temperature environment of the springer cylinder.

In order to extend the life of leather seals, some means of keeping them soft and supple was needed, and the traditional solution was a fat extracted from the shin bones of cattle and called ‘neatsfoot oil’ – ‘neat’ being an old word for ‘cattle’. Unlike other animal fats, neatsfoot oil remained a liquid at room temperature, which allowed it to soak into the leather, and this greatly extended the useful working life of seals, but in time, and especially in the high temperature environment of the springer cylinder, it oxidises and becomes brittle.

In order to extend the useful working life of leather seals, airgun manufacturers used to recommend periodically – after every so many hundred shots – putting a couple of drops of lubricant (usually their own brand) down the transfer port.

In springers that achieved very low muzzle energy, such as 6 ft.lb. target rifles, neatsfoot oil worked well, but if the muzzle energy was raised to the point at which cylinder temperature exceeded 442ºC, it combusted (dieseled), and repeated dieseling shots did the leather seal no good at all though, to be fair, it took a lot of shots to damage the seal to the point at which it failed to do its job.

TRANSFER PORTS