Small air pistol uses small pressurised Co2 cartridges for a propellent.
When *new* the pressure would maintain itself over many months, but now it only holds pressure for a few weeks. Apparently they can replace the seal, but it needs to go back to the workshop and they charge a lot.
The tip of the cartridge is 7mm in diameter, and is pushed on to a pin that pierces it whilst at the same time the cartridge is pushed against the seal.
I've tried using a couple of layers of the silvery metal-impregnated long life bread bag over the end of the cartridge, but it makes for only a slight improvement.
I know that there are materials out there, since I have a japanese cigarette lighter that i never use and it has held its pressure and it works well after twenty years.
What material could i best use to cut out a small washer to sit on the end of the cartridge that would make a good gas tight seal?