I talked about an AR-10 in 6.5x47 with my gunsmith, who specializes in building customized and accurized AR style rifles. He indicated that an AR-15 style would not have the magazine "length" for this round, and we'd have to go with an AR-10 to get that. he was all ready to tackle this, but I don't have sufficient funds to "pull the trigger" on the build, so it's on my wish list.
I think that is essentially what you are looking for, isn't it?