Thank you ALL for all the information. This is all most helpful. It in itself is very enlightening, however it has also given me new possible leads into more Google searches.

The reason for the inquiry is that I am considering a project around a barrel blank I have. The barrel was made by Boots Obermeyer back in the 1980's and was never used. I bought it from the original owner and I am now considering using it. Either to mate it to a 98 Mauser or maybe one of the Lee variants, and there in lies the inquiry for info on the 303.

Thanks again for the suggestions and links.