HI..do I have to expand the neck of the 30-30 case if I am going to reload cast bullets...
Short answer, as others have indicated, is "yes".
How and how much depends on several factors including the design of the bullet and case, alloy hardness, gas check or none, how deep to set the expander plug, and inside and outside diameters. Very small dimensional differences do matter.
I load cast bullets in the 30-30. After sizing I expand with a Lyman M die. As with all sizing operations, the more you work the brass the shorter its life, so I strive for the minimum that will work. One thing I found is that a conventional inside deburring tool doesn't relieve enough inside edge to always prevent lead shaving. Following up with a low angle chamfering tool takes just enough off to increase the taper and prevent shaving. It may only need to be done once. I haven't tested it enough to determine if I need to do it after the first reloading of the case.
With a 30-30 and tubular magazine, you will have to crimp the bullet after seating, taking out the flare. I prefer the Lee factory crimp die. This is another step that works the brass, so the case mouth is the part that takes the most beating from repeated working.
Loading cast bullets can be fun and produce good results, once you have your procedures down pat. It isn't for the lazy, though.
Paul