Fellas, I really appreciate your help. I am surprised at how fast the twists are. My reason for asking is that I am thinking of building a single-shot in one of the .577 BP calibers. If I use a Martini, I will of course be limited on case length. What got me interested in twist rates is that Pac-Nor offers a .577 barrel with a 1:18 twist, which I fear is too quick for soft lead and black powder. But perhaps not.