To those that ask "Why powder coating?" For someone to ask this question indicates he(or she) has not shot many lead rounds! The powder coating replaces the messy lube on the bullets and reduces(almost eliminates) bore leading.
To answer the OP's question! I have run powder coated .357s thru a sizing die and reduced the dia. to .355! This DID NOT damage the powder coating at all, it shined it up a little! I roll crimp ALL my ammo(revolvers only) and shot 240gr 44 lead at 1225fps with no bore leading!
jcelect