As stated above, most .30-30 bullets are either round nose or flat point due to the risk of chain fire in the tube magazine. Bullets at places like Cabela's and other suppliers will have these bullets marked as being for the .30-30. Most factory ammo is also usually either 150 grain or 170 grain.
The fact is that vurtually all .30 cal chamberings use .308 diameter bullets. An exception would be the .303 British which uses a .312 diameter bullet. Some will say that it is not a true .30 cal while others classify it that way. Now it is possible to use other bullets of different shapes in the .30-30. A couple of solutions are to use a single shot action or only load a single round in the magazine, effectively making the typical lever action into a two shot rifle(load one in the chamber and then one in the mag). Another solution from long ago was to use a spiral shaped tube magazine which allowed the tips to be offset from the primers.
In theory you could load any .308 bullet into a .30-30 case and it should chamber and fire. The risk is that someone who is not aware of the dangers of chain fire could use them in a tube magazine...