Abstract: An explosives package is disclosed comprising a plastic tubular container having male and female ends adapted to be coupled with like containers to form a column, and primer and blasting explosives contained therein. The container is open at both ends and has an internal circumferential ring seat. The ring seat and open end of the container enables a cast primer composition to be poured through the open end onto a piston which is in fluid-tight relationship with the ring seat. A capwell thimble is inserted into and retained in the side of the male end of the container so that the closed end of the capwell is situated within the cast primer composition.