Shot placement, shot placement, shot placement.
The 30-30 works fine. With the new Hornady LeverEvolution ammo it almost equals a 308.
Nobody will say the 308 isn't adequate for deer.

I know a person who only hunts in Colorado with a 30-30; for deer, elk and antelope.
Don't feel undergunned with the 30-30. I could tell you story after story of guys with "Magnum" rifles that have run offs from shot game. It happens. Having the latest and greatest uber magnum isn't gonna stop it from happening. What those uber magnums give you is longer distace capability with greater energy at those ranges. Unfortunately a lot of those "magnum" owners don't practice relying on their gun to do the job when the shot was poor causing run offs.