Barrel Vise from Brownells
This is the same vise that I use at Idaho Custom Arms. This system has yet to let me down! In the old shop, it was permanently mounted to the corner of a workbench. In the new shop, I tighten this to the barrel first, then clamp this vise into the 5″ vise on the bench. This method gives me much more flexibility for positioning the action/barrel in whatever orientation that I choose. Both methods have worked great for me. Brownells carries a number of vise inserts (required for operation) in different sizes, so be sure to get the inserts that are a match for your barrel diameter.
Click on the photo head over to Brownells!