There are lots of us out here shooting the 30-30 out of 10 and 14 inch contender barrels and while the 10 loses quite a bit more, the 14 gives up very little over a 20 inch carbine, if you look in your loading manuals, you'll see what velocities are coming out of a 14 inch barrel to compare with the 20 inchers. You should do just fine with the traditional 30-30 bullets that you sugguest. If you want to use it as a single shot or two shooter, you could go to lighter pointed bullets, but that would be if you were comfortable with that idea.
love those carbines,
regards,
Gene