Your gyrojet was made with a nozzle made of powdered metal (high carbon steel). It has a dull gray color. The powder metal was molded at a very high pressure, which resulted in a completely formed nozzle. Then it was heated to just under it’s melting temperature (called “sintering”), which turned it into a solid piece. These have “slots,” not round “ports.” There are two (rare) three, and four slots, some straight and some curved. They are extremely high quality and Mainhardt was very proud of them. They come in 13mm (12.94mm o.d.) and 12mm (12.54mm o.d.). I’ve seen eight or nine variations (dummy, nickel primer, coper primer, 13mm, 12mm) but never a two-slot specimen. However, I do have the factory engineering drawing of one, and Mainhardt said he made them.