How many rounds does it take to wear out the riffiling in a barrel? How much accuracy is lost with a worn out barrel? I was thinking long term, as usual and was wondering about the riffling in my M4 barrel. Do I need an extra barrel, or maybe a complete upper? I have been trying to compile some extra parts for my weapons in general and was thinking in particular about the barrel. If someone that owns an ar type weapon and maybe shoots 500 rounds a year, do they really need an extra barrel? Thoughts and comments??