I slugged the barrel and it came out at .413 so I would need at least a .414 sized bullet. There is an RCBS bullet mold that is made for the 416 that could work according to some other sources I found but I am not sure it would chamber unsized so if anyone casts with this bullet I would like to try a couple so I know what size will chamber correctly.
Thanks for the load info, I have also found some info and the more I find the better.