If the 300s really matter that much to you, you already know what to do. There are a few in the middle ground like 270gr GDs and IIRC 280gr Swifts that may offer more weight without compromising your preferred choice in rifles.
FWIW, Barnes 225gr XPBs, which require a 20" twist, scattered like buckshot from my MGM Contender, a 20" twist. Very disappointing. I also have some FTXs to try, but will have to trim cases if I want to run them in my levergun.
