A 350 Rem Mag is a very simple rebarrel and you need nothing other than a 243 or 308 on an Ruger 77 to make it happen. I did the 375-350 Rem Mag (via PacNor) on a 243 M77. They opened the bolt face and screwed a .375 barrel on it. It feeds great and shoots MOA. The barrel could have been one contour lighter, but it handles well and isn't bad to shoot either.