Iso Propyl Nitrate is not easy to buy, use glass hardener fluid who has Methyl Ethylene Keton Peroxyde.
Ether is difficult to buy in some countries, use engine starter fluid who has Diethylether. Remove propelant from aerosolbox before pouring ether in the bottle with sealed cork/cap.
The lapped contrapiston must be tight in the bore, it can move by pressure of compression and copression screw. In case impossible to move contra piston --> warm up the cylinder and press out the contrapiston. Clean up carefully with steel wool (never use sandpaper!) and mount the contrapiston into the cylinder with oil on .