Are powder coated and polymer coated the same thing?
Sizing can be an issue. You are adding .001-.002 of coating to a cast bullet that may be your bore size target in the first place. You should really slug your barrel(s) to make sure you are loading in the neighborhood the optimum size of +.002 over bore size.
Another issue is that the coating is also adding to the ogive size, which can affect your OAL. A lot of modern day barrels have pretty short throats. Plunk testing is much more critical than it may have been before loading PC'd bullets.