I just built an underhammer rifle in .40 cal (H&A style), and am interested in hearing from those who shoot that caliber. I've only shot .54 to this point. I have a 42" Colerain swamped barrel in 1:48 twist. I almost went with a Green River 36" 1:66 twist, but really like the swamped barrels. What are your barrel specifications? What's your favorite load? Thanks for your input!