Since you don't now a lot about big guns and ballistics why not just buy a nice rifle in 300weatherby magnum with a 26" barrel and sight in 2" high at 100yrds with a decent scope you will be able hit half gallon jugs with ease just aim dead on the target of interest and you could take it on out to 1,000yrds once you learn your rifle. If you do go with the 300weatherby mag I would buy a gun with a muzzle Brake, and you may want to start Reloading this will only make you better and more knowledgable about the sport of shooting.. but for begining long range the caliber mentioned will do it like a 22 shots cans at 50yrds.. the reality of what im saying is you will not need to be a great shot as long as you have a big nice scope. There you go long range made as easy as going to walmart. And save your money for ammo.