A little background: When I first started looking at 50 AE, there were two manufacturers – IMI and Starline. All IMI cases were not-nickel-plated brass, in the IMI some I’s had serifs others not, some cases had brass primers others nickel-plated primers, brass primed had light crimps, all the zero’s were racetracks, the flash holes were not deburred. The IMI-made SPEER-headstamped cases had a dash between the caliber designator (50-AE) like other IMI-made SPEER-headstamped cases, no crimp, racetrack zero’s, flash holes not deburred. Although I do not have an example, at that time Starline advertised both brass and nickel-plated 50 AE cases. The Starline-made SPEER-headstamped cases had a colon in the caliber designator (50:AE), cases were nickel-plated, nickel-plated primers, small lettering, and deburred flash holes. Later MRI-headstamped cases, which came in the same SPEER, INC-marked plastic boxes as the SPEER ammo, had the same colon in the caliber, brass cases, brass primers, small lettering, and deburred flash holes – Starline-made. Your HORNADY-headstamped cases with colon in the caliber I have no doubt are Starline-made like similar cases in the Hornady line with the colon. The HORNADY-headstamped cases I have have a single dot after HORNADY (HORNADY.), brass cases, brass primers, small lettering, and deburred primers – I’ve no doubt they, too, are Starline-made. (This, however, contradicts drawing a Speer-Hornady parallel as a second type of IMI-made SPEER-headstamped cases had a single dot after SPEER (SPEER.), which according to rumor means they were produced on IMI’s US-supplied SCAMP (Small Caliber Ammunition Modernization Program) machinery.) Although your HORNADY cases have the racetrack zero/O they don’t look like either Starline or IMI to me. Look inside to determine if they have deburred flash holes like Starline or have an unusual rise around the flash hole like those found in CBC, S&B, MFS, or PPU cases. I cannot imagine there is enough demand for 50 AE to justify Hornady tooling up to produce a run of 50 AE cases but there are some eager-to-get-into-the-American-market Eastern European firms who might.