the gun is jamming with a double feed -a round most of the way into the chamber, then another round up against the back of the front round, and being squeezed with the slide open (you know, a double feed). any likely reasons/causes why? gun is about 10 years old, and is clean. i'm using winchester white box factory ammo (new). it's copper jacket, brass case, semi wadcutter. please only post of you know what you're talking about. this is my home protection piece, so this is serious to me.