BSA 1916 .303 Converstion to 30-40??? Does anyone have any information about this type of gun?

You need to obtain 30-40 ammunition for it. That particular cartridge is not in great demand anymore and the shells while available they are not easy to find (I reload for mine). You should be able to order some from Cabela's or Midway. I have that caliber in a Model 95 Winchester and am looking forward to hunting with it this fall.