Alter Aeon Online Help

Keywords are:  'skill firearms proficiency'

Skill: firearms proficiency     Lvl 33  Any  (42%)
                                (obscure)   Requires: point-blank combat and quickloading
                                Group: Ranged weapon skills

This skill is unlocked by completing a quest.

Firearms are difficult to load and operate compared to other ranged
weapons, so special training is necessary to allow you to use them.
The secrets of firearms usage are jealously guarded by Don Milano and
the people of Nueva Granada, and they only divulge those secrets to
those that they trust.

Note that this skill allows one to load and unload firearms, and to
fire them safely and accurately.  In order to manufacture cartridges
to use, you will also need to know the 'explosives' tinkering skill.
See 'help build cartridges' for details.