Fixed sentences given for certain categories of crimes (usually drug, alcohol or gun related crimes) are called

The correct answer to the question above is "Mandatory sentencing"

Explanation:

Crime could be interpreted as an act of violation of a laid down government laws and orders which would activate punishment as stated by the same law.

Mandatory sentencing is a pre-calculated mandatory or minimum sentence that offenders serve for certain crimes. Mandatory sentencing varies among different countries. The word pre-calculated is used because, the degree of a particular punishment, which is usually measured in the number of years to be served in Jail by committing a particular crime has been defined already in the country's law. So an offender is already aware of the kind of punishment to be served for law violation, limiting judge's discretion. Mandatory sentencing aims to punish repeat offenders and general law violators. For example, drink driving, possession of hard drugs and a whole lot of other moral crimes.