hey guys new to guns, new to hunting. I am going to try duck hunting this year and my dad gave me a New Haven by mossberg it is a 600at. by my internet research I found that the 600at at is the same as the 500. is this true? or am I barking up the wrong tree? I am looking to replace the barrel as it is a full choke and I was informed that I cannot shoot steel out of this Barrel safely. looking for guidance