I'm going to say something that you already know and that is; You should not be having this problem. If you followed all the basics, then perhaps the next step, is to contact Lyman and see what they have to say. .....
Now then, I personally have not gotten into the Blackhorn-209 but some of the folks around here, that are, are drilling out the vents, on the nipples. I don't recal what size drill but can find out, if you wish. .....
Be Safe !!!