UNCCGrad,
The 60 Partition can be a little tricky to get to shoot, but they group into around inch and sometimes much less in several of my .224 centerfires, including my RAR. Generally faster rifling twists help, but also faster-burning powders and max loads--which help "bump up" the rear core to fit a particular rifle's bore better.
I generally run TAC with the 60 Partition in .223's, and have gotten decent to very good accuracy in several rifles with it, including one with a 1-12 twist. But any powder somewhat faster-burning than Varget would be worth a try, such as Benchmark, and don't be shy about using max loads.
