Ok, here's the brief history of moly coated bullets from a former Hipower master shooter.
When these first hit the scence they were touted as decreasing bullet drop, increasing velocity and decreasing fouling. Well in an effort to keep up with the Jones we all jumped on them. Heres what the consensus seems to be after a few years of competition with them.
When reloading, due to the decreased friction between to bullet and the case one needs to modify the expander ball to increase neck tension. IF you dont your MAY get vertical stringing. According to NECO - the guys that started this whole thing. moly coated bullets have about 40% less neck tension than a standard non coated bullet.
Bullet drop, maybe 0.5 moa less at 600 yards - really not enough to be considered statistically significant. Read this is B.S.
Decreased fouling - YES, this is true. On average you can fire 50-60 % more rounds before accuracy degrades due to fouling. In some match barrels the difference may be as high as 100% increase.
Can you shoot moly and non moly bullets in the same rifle -- YES. however, your bore will foul at a rate soemwhere between the two bullet types. Will it screw up your accuracy? NOT in the 5-6 rifles I have tried it in. YOu just cant go as long between cleanings.
So what are coated bullets good for? Decreasing fouling especially when shooting solid copper bullets in high pressure loads (like magnums). and that's about it.