I tricked out a sniper rifle and had to drop it to pick up another weapon I needed and have since left that area and now its gone but in the gun store it still shows that I own it. How do I get it back?
Owning the gun is different than currently having it equipped. You can own all the guns, but only have up to 4 equipped at any given time. See this question for answers on how to equip guns you already own.