Gunsmith

A gunsmith is a person who repairs, modifies, designs, or builds guns. This occupation differs from an armorer. A gunsmith does factory level repairs, renovation (such as applying metal finishes), and makes modifications and alterations for special uses. Gunsmiths may also apply carvings, engravings and other decorative features to an otherwise finished gun. The environment in which all this takes place often varies depending on the specific locality, with some gun stores featuring one or a handful of individuals while others resemble large scale specialty shops.

Gunsmiths may be employed in:

To pursue the entirety of this trade, a gunsmith must possess skills as a parts fabricator, a metalworker or blacksmith, a woodworker and an artisan; be knowledgeable in shop mathematics, ballistics, chemistry, and materials engineering; be knowledgeable in the use and application of a variety of hand, power, and machinists tools and measuring devices; and be capable of working accurately and precisely. Those who are (self-) employed in small gunsmith shops must also possess skills as small business operators; work effectively with a wide variety of customers; and remain abreast of, and comply with federal, state, and local laws, ordinances, and requirements.

Due to the great breadth of subject matter to be mastered, many gunsmiths specialize in only a few of the skills required of the general gunsmith. Alternatively, some gunsmiths learn many of the skills of the trade, but only apply them to a few weapon types (e.g. only pistols, only shotguns, only specific brands or models).

The primary technical responsibility of gunsmiths is to ensure that the guns work and function safely.

They accomplish this firstly by always properly observing gun safety handling procedures: both in their own actions, and in the actions of their customers and the people around them.

...
Wikipedia