It sounds like the barrel has not been threaded, but its chambered for a 300 Wby Mag. Get the barrel to a gunsmith, if possible, and have him check it to be sure it is not bent. The seller could suspect it is bent and wants to get rid of it.
The good thing about a blank barrel is it can go into a receiver sized for the barrel. An Enfield receiver has square threads, I believe, and a blank barrel can be cut for a square, if needed, or cut for another Weatherby receiver. So if the barrel gets the OK from the 'smith, I would strongly consiider take it if I were looking for a 300 Wby barrel.