The 6.5m/m Carcano rounds used in the Kennedy assasination were, indeed, the WCC 6.5m/m cartridges mentioned here. Evidently originally a contract for Italy, they were resold by the Italian Government and ended up on the surplus market in Canada and the USA. They were originally made in 1954, and known lot numbers are 6000, 6001, 6002, 6003. They had a 162 grain (nominal) bullet weight, RN FMJ GM bullet, and were loaded with 44 grans of WC Ball powder, Army Lots 40816 and 40817. They were made by the Western Cartridge Company Division of Olin Industries, Inc., at the East Alton, Illinois plant.
Through tests covered in the article referenced below, the ammunition proved to be “remarkably consistent” and “neither we nor any of the other groups who tested that ammunition had any misfires, despite its 40 years of shelf life” (at the time of the tests-JLM).
Reference: Wound Ballistics Review, Vol 2, No 2, “Differences in the Wounding Behavior of the Two Bullets That Struck President Kennedy; An Experimental Study,” by John K. Lattimer, Gary Lattimer, Eric Haubner, angus Laidlaw and Val Forgett.