In my opinion it's ok to have a character who is experienced with guns and weaponry, however there should be some kind of trade off like instead of him being a muscular twenty something year old make him an older man so it makes more sense that he's had a lot of time to learn about guns or come up with something else. Maybe he isn't that good at actually using the guns or the ammo his gun uses is very rare. I'm not the GM so I can't force you to do anything, just my thoughts on reading the CS.