You assume correctly, and that's always a good assumption to make with unknown coins! It's not a Crown. An actual crown would be thicker and silver. The portrait of the king is also very crude, unlike a real one, which looked fatter! What you have appears to be some kind of brass costume jewellery piece, or possibly it was a counter at one stage. The 2 lumps on the edge are where there was probably once a mount to attach a chain or something similar. It may not even be from 1823, it's likely that it's Victorian or it could have even been made in the 60's! A proof in 1823 was a coin struck in very limited numbers usually specially prepared dies and blanks, as a kind of trial piece.