Pet peeve of mine: there is not such thing as a .44" "Navy" revolver. Colt made his "Navy" line in .36" and his "Army" line in .44".
O.K. if you get one, spend the extra $20 and get a steel framed model. Colt did not make brass-framed guns. Those are repro-or Confederate copies of Colts. Brass frames, especially the Colts stretch with heavy loads & all it takes is a cylinder-full of heavy loads to ruin the frame. Been there and done that!
The .451" ball loads easier than the .454" ball. The balls cannot handle a heavy charge well because once you load the ball it swages a small donut of lead and that is all the bearing surface there is on the rifling. Push it too fast and the ball simply skips down the rifling, filling the grooves with lead and in no time you are getting very inconsistent rifling shot to shot. The .454" ball has a slightly longer bearing surface and so can handle the faster speed better than the .451" ball but not by much. Conicals have a very long bearing surface and so can handle any charge you can load in that gun.
Be sure to always load an over-powder wad or a grease patch in front of the bullet to prevent chain-fires. The wads are easier to use but I find the grease works better for me by softening fouling with each shot.
They are a lot of fun and a hoot to shoot.
Learn how to take it apart for cleaning (I can forward my own directions I have for civil war re-enactors if you like) and master its loads and you will love it.
The "knock-down" power of these is pathetic by today's standards. I have taken squirrels with them, because they can be that accurate, but that is close to their limitations as far as hunting. Just because it is .44" do not think it is a .44 Mag. It is not even a .44 Special.