Sorry, I noticed you want something for 800 meters. You’re looking for the 7.62 X 51[.308] caliber. Go to the link and see Armalite’s AR-10. There’s also Springfield Armory’s M1A but that needs a lot of care and maintenance.
For someone who is new at this, you might be better getting a good decent hunting rifle with a heavy barrel such as a Remington 700 in .308. You will spend as much on the scope as the rifle if not more.
You won’t be able to hit anything with a Mini30 beyond 400 yards. The design doesn’t allow it.
fr_freak go to a gun shop and try both the 700 and a Browning A-bolt see which one you like best (fits you best).