Is it true that they will shoot jacketed bullets as well as cast?
They shoot jacketed better than cast. Why? Because Marlin boogers up the barrel when cutting dovetails and stamping the nomenclature.
.460" diameter cast , or gas-checked will give you OK accuracy. .458" or .459" will lead up and key-hole. A lot of cast bullets are a giant rip-off for what you get. Cast your own if you are going to shoot cast.
The 405gr Remington JSP will give you one-hole accuracy. It is by far the best bullet value if you are going to purchase jacketted bullets.