A new barrel will certainly help your groups especially if it is fitted to a fully accurized receiver and bedded properly.
In the 270 caliber, there are no better long range bullets out there then the Wildcat Bullets. E-mail Richard Graves at firstname.lastname@example.org
and tell him what you have. I would suspect he will recommend something in the 140-150 gr ULD RBBT range for long range shooting and hunting.
If you want to go long range with the 270 caliber rounds, the best and only bullet choice in my opinion is the Wildcat ULD RBBTs. Best commercial bullet in my opinion would be the 140 gr Accubond but still feel the Wildcats are vastly superior for long range shooting and hunting.