Once you have a load that's accurate, it doesn't matter if the rifling is square or round.. As Dennis said Getz, Rice, Rayl, Hoyle, Colerain and many others are all great, and anyone will work for you. Changing barrels is not just a simple swamp. Touch hole, lugs all have to be considered, and if you haven't done a couple, a skilled builder is your best bet. If you want to go up in caliber, I would have Bobby Hoyt, or Ed Rayl do the job for you. Best of luck with your decision.
Bill