Slug your bore, and measure the diameter of the slug at its widest point. This is what you need your chamber diameter to be (or slightly larger) for your revolver to shoot nicely. At .440", that sounds very undersized, my Pietta Remington has a .452" barrel. mscdirect.com has reamers, or you can have your cylinder reamed by your local gunsmith, or several places online wil also do, such as
http://www.bpstuffllc.com or
http://cylindersmith.com .