Well, since a 405 uses .411-.412 bullets normally I'd say your mould is right where it is supposed to be. Since you are casting with pure lead they are coming out as small as they are going to get. As long as you have a good press mounted push through sizer, you are all set. I like to fill the lube grooves first before sizing so they don't collapse and usually have no trouble sizing down that far. If you want a smaller mould, there are lots of custom mould makers now who can make you a nice lathe bored mould to your specs for a reasonable fee.