What is a good long range caliber?

Im looking to buy a new rifle and i would like to know which caliber would be the most "flat shooting" at long ranges. something that travels relatively flat and straight. What are the best ones in between .243 to somewhere around 7mm-08 or .308 Also could you recommend a good rifle that is roughly... show more Im looking to buy a new rifle and i would like to know which caliber would be the most "flat shooting" at long ranges. something that travels relatively flat and straight.
What are the best ones in between .243 to somewhere around 7mm-08 or .308

Also could you recommend a good rifle that is roughly around $1500 or less. (and that is known for its accuracy)
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