If I had a felony drug charge over 15 years ago, how do I get my rights back?

It was your only conviction, and given the passage of time, it would be wise for you to potentially seek counsel regarding an expungement.

If you have a felony conviction, you can not legally own a gun in Missouri. If your felony is one of the 3 types that are eligible for expungement, you could file a petition for expungement after 20 years have passed since the conviction, but you must prove that you have had no other misdemeanor or felony convictions during that 20-year period.