Definately after break in!! It may take 2 or 3 applications to get the maximum benefit and effective molecular change to the metal. It's also got to be super clean before each application. Jonathan has spent a lot of time on RFC explaining the process. It's not just a coating but physically alters the surface metal of the bore.
Aaro, do a search at RFC for Chief Dave and Molyfusion, he's a dyed in the wool Molyfusion user and his testimony was good enough for me to invest the time and money($25) in it. One of the benefits is reduced friction in the bore, he has certified velocities with his 17hmr of just short of 2800fps.
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