There is no appreciable weight difference between the 500 and the 590; the 590A1 is the model with the heavy barrel which is slightly heavier than both the 500 and 590. The upgrades the 590A1 receives are the metal trigger housing, heavy wall barrel, and metal safety button. The receivers are all the same other than finish, I have two 14" 590 frontends on 500 receivers and one 590A1 frontend on a 590 receiver.