It's not "normal" to be obsessed with anything.
There's a difference between having a keen interest in something and being obsessed with it though. If you are able to deal with the interest without it preventing you from functioning in your day to day life, that's not obsessive. It becomes obsessive when it becomes irrational and persistent. For example, a guy who continually misses work to deal with the interest would be obsessed.
An interest in guns is not necessarily a bad thing if channeled in a positive direction like becoming a gun smith or going into the military. As long as you are interested in the weapon not the anti-social uses they are capable of. In that case it would be wise to get some counseling before it becomes a problem. An obsession with using weapons for the power they give you over others can become a dangerous thing both for yourself and everybody else.