I use a TNW QC upper with a basic Rock River lower.It has been used with a 16" 5.56 barrel. As I had it apart to install a 20" 6.5G barrel, I decided to check the buffer. The spring was a little dirty, but the buffer has started to flare where the metal and plastic parts of the buffer meet.Is this normal? Do I need a heavier buffer and/or spring? I know just enough about AR's to put one together, and then get into trouble trying to find out why it does what it does.