New Mares Force Pneumatic

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The metal rear end pistons if the front shoulder is forward of any seal can be reached by saltwater, but there is no problem if you soak the guns in freshwater and there is a small breather hole in the side of the piston to let water get past the anvil of the shock absorber face with the piston nose clamped on it. You can see on the grouped piston photo that molded pistons extend right up to the piston mushroom head's shank. A second seal further towards the front of the piston keeps water away from the rear end provided it doesn't leak.

If the gun has muzzle relief ports then rinsing water can access the length of the piston forwards of the seal, so you don't need the piston breather hole. In pneumo-vacuum guns the piston nose seals on the anvil face when discharged, so you have to push the piston back slightly to let water in and out when cleaning the gun. I have mentioned this previously on vacuum barrel threads.

 

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In guns with muzzle relief ports the front piston seal, if it has one, cannot enter the region of the muzzle relief ports as it must not emerge from the front end of the inner barrel. In a pneumo-vacuum gun the piston's front seal can be much further forwards on the piston body as the inner barrel can terminate much closer to the shock absorber's anvil face.

These are the aftermarket pistons that Salvimar makes for the earlier Mares coaxial inner barrel guns such as the Sten, Cyrano, Jet and Spark models.

Note that the "O" ring seal sits in plastic, not in metal.

 

[popgun pete]

In the days of all metal pistons there were no problems if the guns were washed/soaked after a dive, a few guns had stainless steel pistons, but most were plated steel using cadmium or zinc. All metal piston had tiny breather holes in the side of the piston to avoid hydraulic lock on the tapered spear tail's insertion.