The shield is designed for clip-on installation onto 20mm, MARK 100 series electric primed ammunition, belted in MARK 2 links. Ten shields are assemblied in each holder and are simultaneously installed, directly from the holder by the hand operated primer shield installation device onto the after ends of the link-round assemblies in the belt of ammunition. Holders are discarded after the shields are installed. The shield serves as a protective cover for the exposed electric primer during handling, magazine loading, etc. or as the round travels through its chuting to the gun. By completely covering the primer, the shield prevents it from contacting any surface which is irradiated by radio-frequency electromagnetic fields, and thereby prevents accidental ignition. The rounds of ammunition are stripped from their links by the feed mechanism and chambered while the link-shield assemblies continue through the feed mechanism and link ejection chute where they are expended.