A piston recovery system is, as its name suggests, a recovery system whereby an ejection charge pressurises a volume between the top of the ejection charge and a piston. As the pressure increases, the piston is forced along the inside of the airframe, pushing a parachute ahead of it, until the parachute is pushed out of the rocket. This provides a smaller volume than would normally need to be pressurised to eject a parachute, and enables smaller ejection charges to be used.

Piston recovery systems are well used, and are, in fact, used on all PML rocket kits. Pistons negate the need for flameproof wadding, and are easy to maintain.

Their disadvantage is that they can, on occasion, jam, but in order to prevent that from occurring, it is advisable before each flight to lightly rub a bar of dry soap over their outside face, to lubricate the piston. This tends to ensure flawless operation of the piston. The ejection charge residue should be regularly cleaned from inside the airframe with a dry cloth, to prevent the piston from jamming.