Working on spec'ing a custom 280AI. I hand load, but have not yet loaded for a 280AI. Two questions - How long do I need the magazine port and ejection port openings in receiver be to allow for loading long for caliber bullets out close to the lands? What is the best twist rate for a 24" barrel in 280AI for range of bullets from 120 grain to 180 grain. Gun will be primarily used for hunting.