Gelli:
First thing I would do is make a list.
List all the different possible categories you could write about.
Semi-autos, revolvers, rifles, shot guns, black powder, hunting, competition shooting, self-defense, calibers (and how each one might be used), long distance shooting, history of firearms, NRA and why/how it started, Creedmor (NY), non-firearms weapons such as swords and knives, other items used as weapons (hammers and cars).
You could then write about each heading.
Form this list into an outline of how you might line them up.
Some ideas!
God bless!!
Michael