RE: lyman great plains hunter 50 cal.
I will check with him and see what he says about the hammer fix (I read in one post that you can heat them and twist them a little although being new, I think like you I would get the company to do it) .. and as far as the nipple I would get myself an Uncle Mike Hot Shot Nipple right away and put thats on. I heard the threads are kind of strange size on them and that the CVA and Traditions will not fit them. But I am sure they are out there on line.
You have a excellent rifle there. If that thing shoots 1/2 as well as my friends rifles shoot, you will be pleased. I have one friend with the GPR that stood in my yard and with out the aid of any rest, knock plastic soda bottles off my target stand from all angles and distances without even breaking a sweat. Needless to say I had my shooting sticks. It might not sound like a hard thing to do, but free standing most of us seldom shoot like that.