I've been working on this set for 6 years now. The last 2 or 3 I've slowly switched over to all BNs. It is quite the challenge. Most coins are 64bns,finding the right coin with the right grade has been tough. In 6 years I have yet to see a decent 15s in anything above 64bn for sale. The early years are brutal,albeit the set would be much easier to finish in RB than BN,but I've got a huge chunk of them already and one of the harder parts were finding BNs from the 40s-late 50s but finally managed to complete that portion, still looking for those ubber rarities. I did recently pick up a 23s in 65BN,They are out there just need to be found.