Gun Nut

Gun Nut is a perk in Fallout 3 and Fallout 4.

Fallout 3
You are obsessed with using and maintaining a wide variety of conventional firearms. With each rank of the Gun Nut perk, you gain an additional 5 points to the Small Guns and Repair skills. With all three ranks, the player gains a +15 bonus to Small Guns and Repair.

Fallout 4
For each rank taken in the Gun Nut perk tree, the Sole Survivor will gain access to a better tier of gun modifications. Gun Nut can be taken four times, each time granting access to an additional rank of gun modifications (ie, Rank 1 of the perk accesses Rank 1 modifications, Rank 2 of the perk accesses Rank 2 modifications, and so on).