There are some advantages to using moly.... but there are some REAL issues with switching back and forth between moly'd bullets and copper in the same barrel.
Unless you have ALL the copper cleaned out of a barrel before you shoot moly it can cause accuracy prolbems..... and unless you have ALL the moly removed from a bore before switching back to copper it can ALSO cause accuracy problems.
Most benchrest and HP shooters make a decision when they install a new barrel as to which one, moly or copper, they are going to put through the new tube. They then stick to that for the entire life of that barrel.
Personally, I've never found the need for the extra hassles.... I shoot copper exclusively..... but Hey, that's just me.
Best to all,
Swampy
Garands forever