Rifle Primers For Sale. Rifle primers are a type of ignition device used in firearms, specifically in rifles. They are used to ignite the gunpowder in the cartridge and propel the bullet out of the barrel. Rifle primers come in two common sizes: large rifle primers and small rifle primers. The size of the primer is determined by the size of the cartridge and the type of firearm it is used in. Rifle primers are different in size and composition from other types of primers such as pistol or shotgun primers. Rifle Primers For Sale.