I'm currently building a custom rifle with a local buddy of mine who runs a research and development machine shop. I just bought a brand new Rem 700 Action/Receiver with Ultra Mag bolt face as my starting point. This is my first ever custom rifle and I'm doing this on a decent budget but not huge. Was thinking 7mm Mag, 300 Win Mag, & 300 RUM as my calibers. I'm gonna buy all the parts for him and he's gonna true everything and build it. My next purchase will be the barrel. I've looked at Hart, Brux, Bartlein, Douglas, and others. I've decided on a #5 contour, fluted with brake. My buddy will thread the blank and do all the custom work. What I don't know is what twist I need and what length blank I need. All suggestions are helpful. Thanks guys!