I used to use 150 hornady sst,140 bergers and h4831,in my 270 out to 600,never had much luck with it after that but I gave up and went to a 6.5 -06.Now thinking of going back to it with a 1-8 twist and shoot some 170 gr bergers or matrix if I can get them.
If you have a 1-10 twist I think a 150 gr. Nosler LRAB might get you out there aways or a 150 berger,something with a BC around .600 should work.My 6.5 shot the Lapua 139 gr to 1200 yards very well and they had a BC around .580.
Always wanted to try the 150 LRAB"s in my 270 but couldn't find any back then,They claim a BC over .600