I believe that many of the 404 shooters are using the ultra mag case to fire form back to 404 for thier plinkin loads.
As far as Hock moulds go, mine at least was a custom mould but I believe they keep the mould data on hand because I have sent some of my bullets to a couple of other 404 shooters and they have had a mould made as well using the ID numbers from my mould. When I sent my data I stipulated the weight and the mould was made to give the required weight. By asking for a 400gn weight with straight ww then lengthened drive bands would more than likely get you there as 50 gn is not much to pick up in weight. I know I get 10-15 gn just by adding Pb to my alloy.