The .260Rem is a great cartridge. It and its AI cousin have won several tactical rifle competitions. It's basicly an updated version of the 6.5x55 Swede.
Honestly, if I were building an AR strictly to kill paper, I'd build it in .243. The ballistics with either the Berger or DTAC (Sierra) 115 grain bullets are very impressive, and it's certainly enough for game up to medium sized deer.
"Those who have long enjoyed privileges as we enjoy, forget, in time, that men have died to win them."
Franklin D. Roosvelt