To create an inventory of weapons in blueprints you can create a base weapon class and derive weapon blueprints from it e.g. pistol blueprint will be a child blueprint from parent base weapon. To create an inventory of weapons, create an array of base weapon where you want your inventory to be stored.
This link should be helpful http://www.tomlooman.com/tutorial-basic-inventory-system-in-blueprint/
I hope this helps
Michael