I have a 10.4 X 47R and am waiting to hear from RCBS about a custom mould. It's a 300+gr. .429 heeled bullet (.410 heel)with a hollow base. I read an article by Ross Sefreid in Rifle magazine in which he was working up loads for an old Brit BP cartridge and he said he filled the hollow base with something. (A) is it advantageous to do that? and (B) what is a good substance to use for that purpose? SW
