Copper John & Brassie

I'm assuming you're talking about the size of the wire and that you're using Ultra-wire, yes?

If so, BR will be fine for #12 and probably #14...smaller than that, you'll want to go to SM or X-SM, most likely.

Not to say it can't be done, but it might be more of a pain in the****than it's worth.

size small is fine for 16 and 18.

Another question. Is it necessary to use lead on these flies or is the wire and bead enough?