A method of sealing an ammunition cartridge during an ammunition manufacturing process. The method including providing a cartridge case having a projectile receiving mouth with an inner surface and applying a thin circumferential film of a liquid light curable sealant to the inner surface. A cured thin circumferential film is formed by curing the thin circumferential film of liquid light curable sealant using an effective curing light from an optical light spectrum. A projectile is inserted into the mouth of the cartridge case with the cured thin circumferential film forming an air and moisture impermeable seal between the inner surface and the projectile.