If you are only using HRBC projectiles you don't gas checks and use any good load data for 180g. If you intend to cast your own, slug the bore and buy a mould to suit, you can get gas check moulds but most of us don't use them. Lube with Alox. Cheers.
I use and would unreservedly recommend CBE bullet molds, particularly the 314-195 fngc and 314-215rngc. Both are specifically designed for the 303 Brit, but will work across a lot of calibres. They feed well from no1 mags and also into Martini action, I have both.