RE: .655 Too tight?
A smaller constriction usually works best with smaller shot. 655 is pretty small. If it patterns well, it'll probably only do so with #6's. The .665 ID choke will probably pattern well with a wider variety of shot sizes. I've got a .665 in my older Browning. It's the same choke system as your 500. It shoots a very tight pattern with both #6's and #4's.