RE: 30 calibers
The 30 caliber does not automatically have more power. Power is derived from a combination of bullet weight and bullet velocity. The 30-30 is a 30 caliber but does not have the so called power of the 270.
I would suggest that if you are interested in this stuff that you purchase the Hornady reloading manuals where you will find about everything there is to know about calibers and ballistics.