A perforating tool includes a charge holder connected to a work string and a perforator fixed in a charge holder disposed along the work string. The perforator includes a cylindrical case, an explosive material, a metal cap, and a detonating cord. The case has a bulkhead at a first end, an open mouth at a second end, and an interior volume. The first end includes a post having a slot. The explosive material is disposed in the interior volume. The metal cap covers the open mouth of the case and has a disk section defined by a separator ring. The separator ring has a structurally weakened zone that encircles the disk section. The detonating cord is received in the slot of the post.