Reading this magazine raises your Guns skill by 10 points (20 points with the Comprehension perk) for 60 seconds (180 seconds with Retention).
The front cover of the magazine depicts numerous Tommy (Thompson submachine) guns, a weapon that isn't available in the base game. It does appear in Honest Hearts in its military form as the .45 Auto SMG. Unfortunately, the foregrip isn't available as a weapon mod.
To the left of the entrance, behind the knocked down chair in the corner.
Behind the scenes
"Milsurp" is short for "military surplus", and is a term used for supplies used by the military, usually guns and ammunition, that is sold or disposed of by the military when no longer needed. Sometimes milsurp are collected by gun collectors and survivalists.