My name is ***** ***** I am a New York State criminal defense lawyer.
Were you convicted of the charge or just charged? If this was only a felony arrest and the case was never prosecuted or did not end in a felony conviction, then there's no reason that this case would keep you from being able to buy a gun.
If you were convicted, on the other hand, that's a problem. Even though the charge is non-violent and even though you were convicted in 1973, the felony would remain on your record and you would have lost your state and Federal gun rights.
Gun rights once lost in NYS are not easy to get back. The state does not expunge criminal convictions, and the governor doesn't generally grant pardons. But there are a couple of things you can try.
The easiest would be for you to apply for a Certificate of Relief from Civil Disabilities to get your civil rights restored. The State of New York makes it clear that if you have a Certificate of Relief from Civil Disabilities, the Federal government will accept it for purpose of restoring your Federal gun rights. You can see that information right on the application form from the state for the certificate.
So, if you don't have a Certificate of Relief, yet you can apply for one. It's free to apply and the Department of Parole will process it for you. Make sure when you fill it out that you specifically make it clear that you are asking for your firearm rights to be restored. When the certificate is granted, that will restore your civil rights in NYS (except the right to run for office) and unless the certificate specifically states that you are not to get your firearms rights back, the FBI should accept it and grant you your gun rights back.
You can read more about the Certificate of Relief and the Certificate of Good Conduct here.