Attachment 309009
Although my picture seemed to upload on it's side, this grain/corn grinder is the same type grinder that Dieselhorses has pictured above and is the same grinder that Willard McBain uses on his U-tube video. I have been using this grinder to bust up my pucks, but not nearly as fine as McBain. I only set the grinder on a very coarse setting and then like McBain, I also use it for just busting up one puck at a time. I do my finish grinding with my ceramic burr coffee grinder.
A slow steady crank is all that is needed to bust up the pucks and I feel that there is a 99.99 % chance that a spark WILL NOT happen because the metal parts of the grinder are not even touching. If it should, I only loose one puck and perhaps some arm hair as I keep my face away from the hopper.
I found that out of all the processes involved in making and then corning BP, busting up the pucks was the part that I just hated the most, before I started using this grain grinder that is. I get coarse granules from this grain grinder that are more the size of coarse rock salt and that size is so much easier to reduce down with the little ceramic burr coffee grinder than the stuff I was ending up with before after busting up the pucks with a mallet.