Today when i was cleaning my gun, i decided to take it apart. It is a 12 gauge Mossburg Model 500 Youth model with a modified accu-choke choke tube. I have only had this gun about a year and its only been shot 700 times or so, but when i took the tube out almost the entire bottom half was missing! I never noticed anything wrong with the gun but obviuiosly something has happened. Have any of you heard of this happening or had this happen to you? Is it just a defect or should i just get a different gun or somethin'.

Thanks for any help.