I have done a couple AR 15 in 22 cal builds, and have had fun doing so and learned the platform pretty well for now. My question is are the lowers any different for a 30 cal versus a 22 cal, Obviously the barrel and upper bolt assembly and carrier would be, but thinking about building one, just because! Point me in the direction of what I need to know or let me know here if you have time to explain the difference between the two calibers thanks Eddie.

Check in the AR Variant  sub forum in the caliber specific FAQ thread at the top.
http://www.ar15.com/forums/t_3_121/492215_AR15_Variants__Caliber_specific_FAQs.html

The 300 Blackout uses an Ar15 Lower. A .308 Win use the larger A10 or LR308 lower.
.308 AR FAQ