Just got a new single cav RCBS mould for my 40/65 with thick sprue plate and cant get good base fillout? Casting 40-1 and tried 720 to 810 temp. Tried WW and boiled Mould , brake cleaner etc. Sprue plate has good machine marks that I used carpenter pencil on came back and used brass brush to open up vent? Do I have a vent problem??