So, the gun fired fine for 75 rounds of this ammo and then stopped working? It isn't an ammo problem.

Even after 500 rounds and never cleaning it, I would doubt you have enough carbon build-up to cause the ejector to start malfunctioning either. Stranger stuff has happened, but normally it takes a lot more ammo than that before you see failures from carbon build-up. I would suspect something else may have jammed the ejector or something in the mag.

Disassemble the gun, clean and relube it. Look for foreign objects like brass in the gun. Also look for broken parts. Also clean the mags. Then function test again.