Following on from my recent post on parachute seal conversions, this is my preferred option for running “O” ring seals.

I use these different design piston heads where the “O” ring sits lower on the piston head (where the locating pin sits). This has several advantages: the “O” ring keeps the piston head retaining pin captive, so it cannot “walk” sideways and score the compression cylinder, and allows material to be removed from the piston head, to increase swept volume, and reduce piston weight. This means a lighter spring can be used for the same power output, or the standard spring will give increased power. I very much prefer the lighter spring option, as it gives a much better firing cycle, and more consistent accuracy.

I also use “O” rings of slightly thinner rubber material (2.8mm instead of 3.0mm standard) as they still seal, but are less prone to damage on insertion, and run with less friction.

Old piston for conversion

New piston head measuring 15mm

Reworked piston head 12.5mm and polished ready for use.