It's the method I've used for at least 30 years for rapid shots on a non-turbo controller. I most commonly used it to unlock the secret Arcade difficulty level

It's the method I've used for at least 30 years for rapid shots on a non-turbo controller. I most commonly used it to unlock the secret Arcade difficulty level on Gradius 3 SNES, but I used it before that point. I was a bit surprised to see that was a semi-secret technique!